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• Should static methods be avoided as much as possible? [closed]

  - by nabina

  While developing an application in OOP, should static methods be avoided as much as possible?

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• Using delegates in C# (Part 2)

  - by rajbk

  Part 1 of this post can be read here. We are now about to see the different syntaxes for invoking a delegate and some c# syntactic sugar which allows you to code faster. We have the following console application. 1: public delegate double Operation(double x, double y); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: Operation op1 = new Operation(Division); 9: double result = op1.Invoke(10, 5); 10: 11: Console.WriteLine(result); 12: Console.ReadLine(); 13: } 14: 15: static double Division(double x, double y) { 16: return x / y; 17: } 18: } Line 1 defines a delegate type called Operation with input parameters (double x, double y) and a return type of double. On Line 8, we create an instance of this delegate and set the target to be a static method called Division (Line 15) On Line 9, we invoke the delegate (one entry in the invocation list). The program outputs 5 when run. The language provides shortcuts for creating a delegate and invoking it (see line 9 and 11). Line 9 is a syntactical shortcut for creating an instance of the Delegate. The C# compiler will infer on its own what the delegate type is and produces intermediate language that creates a new instance of that delegate. Line 11 uses a a syntactical shortcut for invoking the delegate by removing the Invoke method. The compiler sees the line and generates intermediate language which invokes the delegate. When this code is compiled, the generated IL will look exactly like the IL of the compiled code above. 1: public delegate double Operation(double x, double y); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: //shortcut constructor syntax 9: Operation op1 = Division; 10: //shortcut invoke syntax 11: double result = op1(10, 2); 12: 13: Console.WriteLine(result); 14: Console.ReadLine(); 15: } 16: 17: static double Division(double x, double y) { 18: return x / y; 19: } 20: } C# 2.0 introduced Anonymous Methods. Anonymous methods avoid the need to create a separate method that contains the same signature as the delegate type. Instead you write the method body in-line. There is an interesting fact about Anonymous methods and closures which won’t be covered here. Use your favorite search engine ;-)We rewrite our code to use anonymous methods (see line 9): 1: public delegate double Operation(double x, double y); 2:  3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: //Anonymous method 9: Operation op1 = delegate(double x, double y) { 10: return x / y; 11: }; 12: double result = op1(10, 2); 13: 14: Console.WriteLine(result); 15: Console.ReadLine(); 16: } 17: 18: static double Division(double x, double y) { 19: return x / y; 20: } 21: } We could rewrite our delegate to be of a generic type like so (see line 2 and line 9). You will see why soon. 1: //Generic delegate 2: public delegate T Operation<T>(T x, T y); 3:  4: public class Program 5: { 6: [STAThread] 7: static void Main(string[] args) 8: { 9: Operation<double> op1 = delegate(double x, double y) { 10: return x / y; 11: }; 12: double result = op1(10, 2); 13: 14: Console.WriteLine(result); 15: Console.ReadLine(); 16: } 17: 18: static double Division(double x, double y) { 19: return x / y; 20: } 21: } The .NET 3.5 framework introduced a whole set of predefined delegates for us including public delegate TResult Func<T1, T2, TResult>(T1 arg1, T2 arg2); Our code can be modified to use this delegate instead of the one we declared. Our delegate declaration has been removed and line 7 has been changed to use the Func delegate type. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: //Func is a delegate defined in the .NET 3.5 framework 7: Func<double, double, double> op1 = delegate (double x, double y) { 8: return x / y; 9: }; 10: double result = op1(10, 2); 11: 12: Console.WriteLine(result); 13: Console.ReadLine(); 14: } 15: 16: static double Division(double x, double y) { 17: return x / y; 18: } 19: } .NET 3.5 also introduced lambda expressions. A lambda expression is an anonymous function that can contain expressions and statements, and can be used to create delegates or expression tree types. We change our code to use lambda expressions. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: //lambda expression 7: Func<double, double, double> op1 = (x, y) => x / y; 8: double result = op1(10, 2); 9: 10: Console.WriteLine(result); 11: Console.ReadLine(); 12: } 13: 14: static double Division(double x, double y) { 15: return x / y; 16: } 17: } C# 3.0 introduced the keyword var (implicitly typed local variable) where the type of the variable is inferred based on the type of the associated initializer expression. We can rewrite our code to use var as shown below (line 7).  The implicitly typed local variable op1 is inferred to be a delegate of type Func<double, double, double> at compile time. 1: public class Program 2: { 3: [STAThread] 4: static void Main(string[] args) 5: { 6: //implicitly typed local variable 7: var op1 = (x, y) => x / y; 8: double result = op1(10, 2); 9: 10: Console.WriteLine(result); 11: Console.ReadLine(); 12: } 13: 14: static double Division(double x, double y) { 15: return x / y; 16: } 17: } You have seen how we can write code in fewer lines by using a combination of the Func delegate type, implicitly typed local variables and lambda expressions.

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• Pixel Shader Giving Black output

  - by Yashwinder

  I am coding in C# using Windows Forms and the SlimDX API to show the effect of a pixel shader. When I am setting the pixel shader, I am getting a black output screen but if I am not using the pixel shader then I am getting my image rendered on the screen. I have the following C# code using System; using System.Collections.Generic; using System.Linq; using System.Windows.Forms; using System.Runtime.InteropServices; using SlimDX.Direct3D9; using SlimDX; using SlimDX.Windows; using System.Drawing; using System.Threading; namespace WindowsFormsApplication1 { // Vertex structure. [StructLayout(LayoutKind.Sequential)] struct Vertex { public Vector3 Position; public float Tu; public float Tv; public static int SizeBytes { get { return Marshal.SizeOf(typeof(Vertex)); } } public static VertexFormat Format { get { return VertexFormat.Position | VertexFormat.Texture1; } } } static class Program { public static Device D3DDevice; // Direct3D device. public static VertexBuffer Vertices; // Vertex buffer object used to hold vertices. public static Texture Image; // Texture object to hold the image loaded from a file. public static int time; // Used for rotation caculations. public static float angle; // Angle of rottaion. public static Form1 Window =new Form1(); public static string filepath; static VertexShader vertexShader = null; static ConstantTable constantTable = null; static ImageInformation info; [STAThread] static void Main() { filepath = "C:\\Users\\Public\\Pictures\\Sample Pictures\\Garden.jpg"; info = new ImageInformation(); info = ImageInformation.FromFile(filepath); PresentParameters presentParams = new PresentParameters(); // Below are the required bare mininum, needed to initialize the D3D device. presentParams.BackBufferHeight = info.Height; // BackBufferHeight, set to the Window's height. presentParams.BackBufferWidth = info.Width+200; // BackBufferWidth, set to the Window's width. presentParams.Windowed =true; presentParams.DeviceWindowHandle = Window.panel2 .Handle; // DeviceWindowHandle, set to the Window's handle. // Create the device. D3DDevice = new Device(new Direct3D (), 0, DeviceType.Hardware, Window.Handle, CreateFlags.HardwareVertexProcessing, presentParams); // Create the vertex buffer and fill with the triangle vertices. (Non-indexed) // Remember 3 vetices for a triangle, 2 tris per quad = 6. Vertices = new VertexBuffer(D3DDevice, 6 * Vertex.SizeBytes, Usage.WriteOnly, VertexFormat.None, Pool.Managed); DataStream stream = Vertices.Lock(0, 0, LockFlags.None); stream.WriteRange(BuildVertexData()); Vertices.Unlock(); // Create the texture. Image = Texture.FromFile(D3DDevice,filepath ); // Turn off culling, so we see the front and back of the triangle D3DDevice.SetRenderState(RenderState.CullMode, Cull.None); // Turn off lighting D3DDevice.SetRenderState(RenderState.Lighting, false); ShaderBytecode sbcv = ShaderBytecode.CompileFromFile("C:\\Users\\yashwinder singh\\Desktop\\vertexShader.vs", "vs_main", "vs_1_1", ShaderFlags.None); constantTable = sbcv.ConstantTable; vertexShader = new VertexShader(D3DDevice, sbcv); ShaderBytecode sbc = ShaderBytecode.CompileFromFile("C:\\Users\\yashwinder singh\\Desktop\\pixelShader.txt", "ps_main", "ps_3_0", ShaderFlags.None); PixelShader ps = new PixelShader(D3DDevice, sbc); VertexDeclaration vertexDecl = new VertexDeclaration(D3DDevice, new[] { new VertexElement(0, 0, DeclarationType.Float3, DeclarationMethod.Default, DeclarationUsage.PositionTransformed, 0), new VertexElement(0, 12, DeclarationType.Float2 , DeclarationMethod.Default, DeclarationUsage.TextureCoordinate , 0), VertexElement.VertexDeclarationEnd }); Application.EnableVisualStyles(); MessagePump.Run(Window, () => { // Clear the backbuffer to a black color. D3DDevice.Clear(ClearFlags.Target | ClearFlags.ZBuffer, Color.Black, 1.0f, 0); // Begin the scene. D3DDevice.BeginScene(); // Setup the world, view and projection matrices. //D3DDevice.VertexShader = vertexShader; //D3DDevice.PixelShader = ps; // Render the vertex buffer. D3DDevice.SetStreamSource(0, Vertices, 0, Vertex.SizeBytes); D3DDevice.VertexFormat = Vertex.Format; // Setup our texture. Using Textures introduces the texture stage states, // which govern how Textures get blended together (in the case of multiple // Textures) and lighting information. D3DDevice.SetTexture(0, Image); // Now drawing 2 triangles, for a quad. D3DDevice.DrawPrimitives(PrimitiveType.TriangleList , 0, 2); // End the scene. D3DDevice.EndScene(); // Present the backbuffer contents to the screen. D3DDevice.Present(); }); if (Image != null) Image.Dispose(); if (Vertices != null) Vertices.Dispose(); if (D3DDevice != null) D3DDevice.Dispose(); } private static Vertex[] BuildVertexData() { Vertex[] vertexData = new Vertex[6]; vertexData[0].Position = new Vector3(-1.0f, 1.0f, 0.0f); vertexData[0].Tu = 0.0f; vertexData[0].Tv = 0.0f; vertexData[1].Position = new Vector3(-1.0f, -1.0f, 0.0f); vertexData[1].Tu = 0.0f; vertexData[1].Tv = 1.0f; vertexData[2].Position = new Vector3(1.0f, 1.0f, 0.0f); vertexData[2].Tu = 1.0f; vertexData[2].Tv = 0.0f; vertexData[3].Position = new Vector3(-1.0f, -1.0f, 0.0f); vertexData[3].Tu = 0.0f; vertexData[3].Tv = 1.0f; vertexData[4].Position = new Vector3(1.0f, -1.0f, 0.0f); vertexData[4].Tu = 1.0f; vertexData[4].Tv = 1.0f; vertexData[5].Position = new Vector3(1.0f, 1.0f, 0.0f); vertexData[5].Tu = 1.0f; vertexData[5].Tv = 0.0f; return vertexData; } } } And my pixel shader and vertex shader code are as following // Pixel shader input structure struct PS_INPUT { float4 Position : POSITION; float2 Texture : TEXCOORD0; }; // Pixel shader output structure struct PS_OUTPUT { float4 Color : COLOR0; }; // Global variables sampler2D Tex0; // Name: Simple Pixel Shader // Type: Pixel shader // Desc: Fetch texture and blend with constant color // PS_OUTPUT ps_main( in PS_INPUT In ) { PS_OUTPUT Out; //create an output pixel Out.Color = tex2D(Tex0, In.Texture); //do a texture lookup Out.Color *= float4(0.9f, 0.8f, 0.0f, 1); //do a simple effect return Out; //return output pixel } // Vertex shader input structure struct VS_INPUT { float4 Position : POSITION; float2 Texture : TEXCOORD0; }; // Vertex shader output structure struct VS_OUTPUT { float4 Position : POSITION; float2 Texture : TEXCOORD0; }; // Global variables float4x4 WorldViewProj; // Name: Simple Vertex Shader // Type: Vertex shader // Desc: Vertex transformation and texture coord pass-through // VS_OUTPUT vs_main( in VS_INPUT In ) { VS_OUTPUT Out; //create an output vertex Out.Position = mul(In.Position, WorldViewProj); //apply vertex transformation Out.Texture = In.Texture; //copy original texcoords return Out; //return output vertex }

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• "Service Unavailable" when browsing to static HTML page in non-application IIS website on Windows 2003 (possibly SharePoint WSS 2.0 related?)

  - by Jordan Rieger

  Background: My client has an old Pentium III Windows 2003 server whose 16/36 GB disks are dying. On it he has a database-driven web site and email application that needs further customization by a developer (me). First we need to get it working on the new server. The original developer is no longer available to provide a system setup guide. So my client got a tech who imaged the old drives over to the new server and managed to get it booting. But the IIS-driven site no longer works. In fact it seems that IIS itself does not work. Problem: Service Unavailable when attempting to browse from the server itself to the URL for a local Web Site called test which I setup in IIS to serve a single static index.htm file. This I did to isolate the problem, and eliminate the client's application from the equation. The site is setup on port 80 with the host header "test.myclientsdomain.com", and I used the etc\hosts file to point that host at the local IP. I know the host entry took effect because I can ping it. When doing an iisreset, I get: Attempting start... Restart attempt failed. IIS Admin Service or a service dependent on IIS Admin is not active. It most likely failed to start, which may mean that it's disabled. Despite this message, the services all stay in the Started state. The only relevant System event logs I found are: Event Type: Error Event Source: W3SVC Event Category: None Event ID: 1002 Date: 11/4/2012 Time: 11:04:47 PM User: N/A Computer: ALPHA1 Description: Application pool 'DefaultAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool. Event Type: Error Event Source: W3SVC Event Category: None Event ID: 1039 Date: 11/4/2012 Time: 11:13:12 PM User: N/A Computer: ALPHA1 Description: A process serving application pool 'DefaultAppPool' reported a failure. The process id was '5636'. The data field contains the error number. Data: 0000: 7e 00 07 80 ~.. And one Application event log: Event Type: Error Event Source: Windows SharePoint Services 2.0 Event Category: None Event ID: 1000 Date: 11/4/2012 Time: 11:34:04 PM User: N/A Computer: ALPHA1 Description: #50070: Unable to connect to the database STS_Config on ALPHA2\SharePoint. Check the database connection information and make sure that the database server is running. That last log tells me that the tech may have initially tried to have both the old and the new server running, by renaming the new server from ALPHA1 to ALPHA2. And perhaps SharePoint grabbed onto that change, and now can't tell that the machine name has been switched back to the old ALPHA1. But why would SharePoint interfere with a static IIS web site serving a single HTML file? The test site is not even within an Application pool (I clicked the Remove button.) What I have tried/eliminated: No relevant services seem to be disabled: IIS Admin, WWW Publishing, Sharepoint Timer Giving Full Control to All Users/Everyone on the c:\inetpub\test folder serving my test site. I can connect to and query the local SharePoint config database (ALPHA1\SHAREPOINT\STS_CONFIG) from SSMS. But when I try to do stsadm -o setconfigdb -connect -databaseserver ALPHA1\SHAREPOINT it tells me The SharePoint admininstration port does not exist. Please use stsadm.exe to create it. And when I do that, using the port 9487 specified in the IIS SharePoint Admin site config, it tells me the port is already in use. Needless to say, simply browsing to the admin site gives me a similar error about being unable to reach the config database. I didn't want to go further down the SharePoint path as it may be completed unrelated to my IIS issue, and I don't even know yet if SharePoint is required for this application to work. The app itself is ASP.Net/C#/Silverlight and a little MS Word integration (maybe that's where the SharePoint stuff comes in.)

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• Problems extracting information from RSS feed description field

  - by Graeme

  Hi, I've built an iPhone application using the parsing code from the TopSongs sample iPhone application. I've hit a problem though - the feed I'm trying to parse data from doesn't have a separate field for every piece of information (i.e. if it was for a feed about dogs, all the information such as dog type, dog age and dog price is contained in the feed. However, the TopSongs app relies on information having its own tags, so instead of using it uses and . So my question is this. How do I extract this information from the description field so that it can be parsed using the TopSongs parser? Can you somehow extract the dog age, price and type information using Yahoo Pipes and use that RSS feed for the feed? Or is there code that I can add to do it in application? Update: To view the code of my application parser (based on the TopSongs Core Data Apple provided application, see below. Here's a sample of one item from the the actual RSS feed I'm using (the description is longer, and has status,size, and a couple of other fields, but they're all formatted the same.: <item> <title>MOE, MARGRET STREET</title> <description> <b>District/Region:</b>&nbsp;REGION 09</br><b>Location:</b>&nbsp;MOE</br><b>Name:</b>&nbsp;MARGRET STREET</br></description> <pubDate>Thu,11 Mar 2010 05:43:03 GMT</pubDate> <guid>1266148</guid> </item> /* File: iTunesRSSImporter.m Abstract: Downloads, parses, and imports the iTunes top songs RSS feed into Core Data. Version: 1.1 Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple Inc. ("Apple") in consideration of your agreement to the following terms, and your use, installation, modification or redistribution of this Apple software constitutes acceptance of these terms. If you do not agree with these terms, please do not use, install, modify or redistribute this Apple software. In consideration of your agreement to abide by the following terms, and subject to these terms, Apple grants you a personal, non-exclusive license, under Apple's copyrights in this original Apple software (the "Apple Software"), to use, reproduce, modify and redistribute the Apple Software, with or without modifications, in source and/or binary forms; provided that if you redistribute the Apple Software in its entirety and without modifications, you must retain this notice and the following text and disclaimers in all such redistributions of the Apple Software. Neither the name, trademarks, service marks or logos of Apple Inc. may be used to endorse or promote products derived from the Apple Software without specific prior written permission from Apple. Except as expressly stated in this notice, no other rights or licenses, express or implied, are granted by Apple herein, including but not limited to any patent rights that may be infringed by your derivative works or by other works in which the Apple Software may be incorporated. The Apple Software is provided by Apple on an "AS IS" basis. APPLE MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS. IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION, MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Copyright (C) 2009 Apple Inc. All Rights Reserved. */ #import "iTunesRSSImporter.h" #import "Song.h" #import "Category.h" #import "CategoryCache.h" #import <libxml/tree.h> // Function prototypes for SAX callbacks. This sample implements a minimal subset of SAX callbacks. // Depending on your application's needs, you might want to implement more callbacks. static void startElementSAX(void *context, const xmlChar *localname, const xmlChar *prefix, const xmlChar *URI, int nb_namespaces, const xmlChar **namespaces, int nb_attributes, int nb_defaulted, const xmlChar **attributes); static void endElementSAX(void *context, const xmlChar *localname, const xmlChar *prefix, const xmlChar *URI); static void charactersFoundSAX(void *context, const xmlChar *characters, int length); static void errorEncounteredSAX(void *context, const char *errorMessage, ...); // Forward reference. The structure is defined in full at the end of the file. static xmlSAXHandler simpleSAXHandlerStruct; // Class extension for private properties and methods. @interface iTunesRSSImporter () @property BOOL storingCharacters; @property (nonatomic, retain) NSMutableData *characterBuffer; @property BOOL done; @property BOOL parsingASong; @property NSUInteger countForCurrentBatch; @property (nonatomic, retain) Song *currentSong; @property (nonatomic, retain) NSURLConnection *rssConnection; @property (nonatomic, retain) NSDateFormatter *dateFormatter; // The autorelease pool property is assign because autorelease pools cannot be retained. @property (nonatomic, assign) NSAutoreleasePool *importPool; @end static double lookuptime = 0; @implementation iTunesRSSImporter @synthesize iTunesURL, delegate, persistentStoreCoordinator; @synthesize rssConnection, done, parsingASong, storingCharacters, currentSong, countForCurrentBatch, characterBuffer, dateFormatter, importPool; - (void)dealloc { [iTunesURL release]; [characterBuffer release]; [currentSong release]; [rssConnection release]; [dateFormatter release]; [persistentStoreCoordinator release]; [insertionContext release]; [songEntityDescription release]; [theCache release]; [super dealloc]; } - (void)main { self.importPool = [[NSAutoreleasePool alloc] init]; if (delegate && [delegate respondsToSelector:@selector(importerDidSave:)]) { [[NSNotificationCenter defaultCenter] addObserver:delegate selector:@selector(importerDidSave:) name:NSManagedObjectContextDidSaveNotification object:self.insertionContext]; } done = NO; self.dateFormatter = [[[NSDateFormatter alloc] init] autorelease]; [dateFormatter setDateStyle:NSDateFormatterLongStyle]; [dateFormatter setTimeStyle:NSDateFormatterNoStyle]; // necessary because iTunes RSS feed is not localized, so if the device region has been set to other than US // the date formatter must be set to US locale in order to parse the dates [dateFormatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"US"] autorelease]]; self.characterBuffer = [NSMutableData data]; NSURLRequest *theRequest = [NSURLRequest requestWithURL:iTunesURL]; // create the connection with the request and start loading the data rssConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self]; // This creates a context for "push" parsing in which chunks of data that are not "well balanced" can be passed // to the context for streaming parsing. The handler structure defined above will be used for all the parsing. // The second argument, self, will be passed as user data to each of the SAX handlers. The last three arguments // are left blank to avoid creating a tree in memory. context = xmlCreatePushParserCtxt(&simpleSAXHandlerStruct, self, NULL, 0, NULL); if (rssConnection != nil) { do { [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; } while (!done); } // Display the total time spent finding a specific object for a relationship NSLog(@"lookup time %f", lookuptime); // Release resources used only in this thread. xmlFreeParserCtxt(context); self.characterBuffer = nil; self.dateFormatter = nil; self.rssConnection = nil; self.currentSong = nil; [theCache release]; theCache = nil; NSError *saveError = nil; NSAssert1([insertionContext save:&saveError], @"Unhandled error saving managed object context in import thread: %@", [saveError localizedDescription]); if (delegate && [delegate respondsToSelector:@selector(importerDidSave:)]) { [[NSNotificationCenter defaultCenter] removeObserver:delegate name:NSManagedObjectContextDidSaveNotification object:self.insertionContext]; } if (self.delegate != nil && [self.delegate respondsToSelector:@selector(importerDidFinishParsingData:)]) { [self.delegate importerDidFinishParsingData:self]; } [importPool release]; self.importPool = nil; } - (NSManagedObjectContext *)insertionContext { if (insertionContext == nil) { insertionContext = [[NSManagedObjectContext alloc] init]; [insertionContext setPersistentStoreCoordinator:self.persistentStoreCoordinator]; } return insertionContext; } - (void)forwardError:(NSError *)error { if (self.delegate != nil && [self.delegate respondsToSelector:@selector(importer:didFailWithError:)]) { [self.delegate importer:self didFailWithError:error]; } } - (NSEntityDescription *)songEntityDescription { if (songEntityDescription == nil) { songEntityDescription = [[NSEntityDescription entityForName:@"Song" inManagedObjectContext:self.insertionContext] retain]; } return songEntityDescription; } - (CategoryCache *)theCache { if (theCache == nil) { theCache = [[CategoryCache alloc] init]; theCache.managedObjectContext = self.insertionContext; } return theCache; } - (Song *)currentSong { if (currentSong == nil) { currentSong = [[Song alloc] initWithEntity:self.songEntityDescription insertIntoManagedObjectContext:self.insertionContext]; } return currentSong; } #pragma mark NSURLConnection Delegate methods // Forward errors to the delegate. - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { [self performSelectorOnMainThread:@selector(forwardError:) withObject:error waitUntilDone:NO]; // Set the condition which ends the run loop. done = YES; } // Called when a chunk of data has been downloaded. - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { // Process the downloaded chunk of data. xmlParseChunk(context, (const char *)[data bytes], [data length], 0); } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { // Signal the context that parsing is complete by passing "1" as the last parameter. xmlParseChunk(context, NULL, 0, 1); context = NULL; // Set the condition which ends the run loop. done = YES; } #pragma mark Parsing support methods static const NSUInteger kImportBatchSize = 20; - (void)finishedCurrentSong { parsingASong = NO; self.currentSong = nil; countForCurrentBatch++; // Periodically purge the autorelease pool and save the context. The frequency of this action may need to be tuned according to the // size of the objects being parsed. The goal is to keep the autorelease pool from growing too large, but // taking this action too frequently would be wasteful and reduce performance. if (countForCurrentBatch == kImportBatchSize) { [importPool release]; self.importPool = [[NSAutoreleasePool alloc] init]; NSError *saveError = nil; NSAssert1([insertionContext save:&saveError], @"Unhandled error saving managed object context in import thread: %@", [saveError localizedDescription]); countForCurrentBatch = 0; } } /* Character data is appended to a buffer until the current element ends. */ - (void)appendCharacters:(const char *)charactersFound length:(NSInteger)length { [characterBuffer appendBytes:charactersFound length:length]; } - (NSString *)currentString { // Create a string with the character data using UTF-8 encoding. UTF-8 is the default XML data encoding. NSString *currentString = [[[NSString alloc] initWithData:characterBuffer encoding:NSUTF8StringEncoding] autorelease]; [characterBuffer setLength:0]; return currentString; } @end #pragma mark SAX Parsing Callbacks // The following constants are the XML element names and their string lengths for parsing comparison. // The lengths include the null terminator, to ensure exact matches. static const char *kName_Item = "item"; static const NSUInteger kLength_Item = 5; static const char *kName_Title = "title"; static const NSUInteger kLength_Title = 6; static const char *kName_Category = "category"; static const NSUInteger kLength_Category = 9; static const char *kName_Itms = "itms"; static const NSUInteger kLength_Itms = 5; static const char *kName_Artist = "description"; static const NSUInteger kLength_Artist = 7; static const char *kName_Album = "description"; static const NSUInteger kLength_Album = 6; static const char *kName_ReleaseDate = "releasedate"; static const NSUInteger kLength_ReleaseDate = 12; /* This callback is invoked when the importer finds the beginning of a node in the XML. For this application, out parsing needs are relatively modest - we need only match the node name. An "item" node is a record of data about a song. In that case we create a new Song object. The other nodes of interest are several of the child nodes of the Song currently being parsed. For those nodes we want to accumulate the character data in a buffer. Some of the child nodes use a namespace prefix. */ static void startElementSAX(void *parsingContext, const xmlChar *localname, const xmlChar *prefix, const xmlChar *URI, int nb_namespaces, const xmlChar **namespaces, int nb_attributes, int nb_defaulted, const xmlChar **attributes) { iTunesRSSImporter *importer = (iTunesRSSImporter *)parsingContext; // The second parameter to strncmp is the name of the element, which we known from the XML schema of the feed. // The third parameter to strncmp is the number of characters in the element name, plus 1 for the null terminator. if (prefix == NULL && !strncmp((const char *)localname, kName_Item, kLength_Item)) { importer.parsingASong = YES; } else if (importer.parsingASong && ( (prefix == NULL && (!strncmp((const char *)localname, kName_Title, kLength_Title) || !strncmp((const char *)localname, kName_Category, kLength_Category))) || ((prefix != NULL && !strncmp((const char *)prefix, kName_Itms, kLength_Itms)) && (!strncmp((const char *)localname, kName_Artist, kLength_Artist) || !strncmp((const char *)localname, kName_Album, kLength_Album) || !strncmp((const char *)localname, kName_ReleaseDate, kLength_ReleaseDate))) )) { importer.storingCharacters = YES; } } /* This callback is invoked when the parse reaches the end of a node. At that point we finish processing that node, if it is of interest to us. For "item" nodes, that means we have completed parsing a Song object. We pass the song to a method in the superclass which will eventually deliver it to the delegate. For the other nodes we care about, this means we have all the character data. The next step is to create an NSString using the buffer contents and store that with the current Song object. */ static void endElementSAX(void *parsingContext, const xmlChar *localname, const xmlChar *prefix, const xmlChar *URI) { iTunesRSSImporter *importer = (iTunesRSSImporter *)parsingContext; if (importer.parsingASong == NO) return; if (prefix == NULL) { if (!strncmp((const char *)localname, kName_Item, kLength_Item)) { [importer finishedCurrentSong]; } else if (!strncmp((const char *)localname, kName_Title, kLength_Title)) { importer.currentSong.title = importer.currentString; } else if (!strncmp((const char *)localname, kName_Category, kLength_Category)) { double before = [NSDate timeIntervalSinceReferenceDate]; Category *category = [importer.theCache categoryWithName:importer.currentString]; double delta = [NSDate timeIntervalSinceReferenceDate] - before; lookuptime += delta; importer.currentSong.category = category; } } else if (!strncmp((const char *)prefix, kName_Itms, kLength_Itms)) { if (!strncmp((const char *)localname, kName_Artist, kLength_Artist)) { NSString *string = importer.currentSong.artist; NSArray *strings = [string componentsSeparatedByString: @", "]; //importer.currentSong.artist = importer.currentString; } else if (!strncmp((const char *)localname, kName_Album, kLength_Album)) { importer.currentSong.album = importer.currentString; } else if (!strncmp((const char *)localname, kName_ReleaseDate, kLength_ReleaseDate)) { NSString *dateString = importer.currentString; importer.currentSong.releaseDate = [importer.dateFormatter dateFromString:dateString]; } } importer.storingCharacters = NO; } /* This callback is invoked when the parser encounters character data inside a node. The importer class determines how to use the character data. */ static void charactersFoundSAX(void *parsingContext, const xmlChar *characterArray, int numberOfCharacters) { iTunesRSSImporter *importer = (iTunesRSSImporter *)parsingContext; // A state variable, "storingCharacters", is set when nodes of interest begin and end. // This determines whether character data is handled or ignored. if (importer.storingCharacters == NO) return; [importer appendCharacters:(const char *)characterArray length:numberOfCharacters]; } /* A production application should include robust error handling as part of its parsing implementation. The specifics of how errors are handled depends on the application. */ static void errorEncounteredSAX(void *parsingContext, const char *errorMessage, ...) { // Handle errors as appropriate for your application. NSCAssert(NO, @"Unhandled error encountered during SAX parse."); } // The handler struct has positions for a large number of callback functions. If NULL is supplied at a given position, // that callback functionality won't be used. Refer to libxml documentation at http://www.xmlsoft.org for more information // about the SAX callbacks. static xmlSAXHandler simpleSAXHandlerStruct = { NULL, /* internalSubset */ NULL, /* isStandalone */ NULL, /* hasInternalSubset */ NULL, /* hasExternalSubset */ NULL, /* resolveEntity */ NULL, /* getEntity */ NULL, /* entityDecl */ NULL, /* notationDecl */ NULL, /* attributeDecl */ NULL, /* elementDecl */ NULL, /* unparsedEntityDecl */ NULL, /* setDocumentLocator */ NULL, /* startDocument */ NULL, /* endDocument */ NULL, /* startElement*/ NULL, /* endElement */ NULL, /* reference */ charactersFoundSAX, /* characters */ NULL, /* ignorableWhitespace */ NULL, /* processingInstruction */ NULL, /* comment */ NULL, /* warning */ errorEncounteredSAX, /* error */ NULL, /* fatalError //: unused error() get all the errors */ NULL, /* getParameterEntity */ NULL, /* cdataBlock */ NULL, /* externalSubset */ XML_SAX2_MAGIC, // NULL, startElementSAX, /* startElementNs */ endElementSAX, /* endElementNs */ NULL, /* serror */ }; Thanks.

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• Why does my performance slow to a crawl I move methods into a base class?

  - by Juliet

  I'm writing different implementations of immutable binary trees in C#, and I wanted my trees to inherit some common methods from a base class. However, I find. I have lots of binary tree data structures to implement, and I wanted move some common methods into in a base binary tree class. Unfortunately, classes which derive from the base class are abysmally slow. Non-derived classes perform adequately. Here are two nearly identical implementations of an AVL tree to demonstrate: AvlTree: http://pastebin.com/V4WWUAyT DerivedAvlTree: http://pastebin.com/PussQDmN The two trees have the exact same code, but I've moved the DerivedAvlTree.Insert method in base class. Here's a test app: using System; using System.Collections.Generic; using System.Diagnostics; using System.Linq; using Juliet.Collections.Immutable; namespace ConsoleApplication1 { class Program { const int VALUE_COUNT = 5000; static void Main(string[] args) { var avlTreeTimes = TimeIt(TestAvlTree); var derivedAvlTreeTimes = TimeIt(TestDerivedAvlTree); Console.WriteLine("avlTreeTimes: {0}, derivedAvlTreeTimes: {1}", avlTreeTimes, derivedAvlTreeTimes); } static double TimeIt(Func<int, int> f) { var seeds = new int[] { 314159265, 271828183, 231406926, 141421356, 161803399, 266514414, 15485867, 122949829, 198491329, 42 }; var times = new List<double>(); foreach (int seed in seeds) { var sw = Stopwatch.StartNew(); f(seed); sw.Stop(); times.Add(sw.Elapsed.TotalMilliseconds); } // throwing away top and bottom results times.Sort(); times.RemoveAt(0); times.RemoveAt(times.Count - 1); return times.Average(); } static int TestAvlTree(int seed) { var rnd = new System.Random(seed); var avlTree = AvlTree<double>.Create((x, y) => x.CompareTo(y)); for (int i = 0; i < VALUE_COUNT; i++) { avlTree = avlTree.Insert(rnd.NextDouble()); } return avlTree.Count; } static int TestDerivedAvlTree(int seed) { var rnd = new System.Random(seed); var avlTree2 = DerivedAvlTree<double>.Create((x, y) => x.CompareTo(y)); for (int i = 0; i < VALUE_COUNT; i++) { avlTree2 = avlTree2.Insert(rnd.NextDouble()); } return avlTree2.Count; } } } AvlTree: inserts 5000 items in 121 ms DerivedAvlTree: inserts 5000 items in 2182 ms My profiler indicates that the program spends an inordinate amount of time in BaseBinaryTree.Insert. Anyone whose interested can see the EQATEC log file I've created with the code above (you'll need EQATEC profiler to make sense of file). I really want to use a common base class for all of my binary trees, but I can't do that if performance will suffer. What causes my DerivedAvlTree to perform so badly, and what can I do to fix it?

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• How come my Apache can't read my media folder, but it can load the site? (static files don't work)

  - by Alex

  Alias /media/ /home/matt/repos/hello/media <Directory /home/matt/repos/hello/media> Options -Indexes Order deny,allow Allow from all </Directory> WSGIScriptAlias / /home/matt/repos/hello/wsgi/django.wsgi /media is my directory. When I go to mydomain.com/media/, it says 403 Forbidden. And, the rest of my site doesn't work because all static files are 404s. Why? The page loads. Just not the media folder. Edit: hello is my project folder. I have tried 777 all my permissions of that folder.

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• How to configure squid for retrieving (and caching) directly my static resources?

  - by fabien7474

  I have an Apache/Tomcat/Spring tc Server running on CentOS EC2 VM. I would like to install squid on the same machine as a proxy for retrieving (directly i.e. without forwarding the request to Apache/Tomcat) and caching static content ONLY identified by URIs : /images, /css or /js. Other URIs should be forwarded to the normal Web Server and not cached. Since I am a newbie, I didn't find from squid documentation how to configure squid for this desired behavior (and if it is even possible). Could you please help me and tell me how should I configure squid for this purpose? Thank you.

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• How to stop Nginx sending static file requests to the CakePHP app controller when running Cake in a

  - by Throlkim

  I'm trying to run a CakePHP app from within a subfolder on Nginx, but the static files are not being found and are instead being passed to the app controller. Here's my current config: location /uniquetv { index index.php index.html; if (-f $request_filename) { break; } if (!-e $request_filename) { rewrite ^/uniquetv(.+)$ /uniquetv/webroot/$1 last; break; } } location /uniquetv/webroot { index index.php; if (!-e $request_filename) { rewrite ^/uniquetv/webroot/(.+)$ /uniquetv/webroot/index.php?url=$1 last; break; } } Any ideas? :)

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• how to? 1 domain name, 1 ISP Static IP, 1 router, 3 physical web Servers

  - by buliwyf

  I have 1 Static IP from my ISP, 58.59.60.61 I have 3 local physical web servers: Win2008 IIS 7, local IP 192.168.10.11, mydomain.com Ubuntu Apache2, local IP 192.168.10.12, subdomain1.mydomain.com Win2003 IIS 6, local IP 192.168.10.13, subdomain2.mydomain.com I have 1 domain name, mydomain.com. It is configured this way: Host(A), @, 58.59.60.61 Host(A), subdomain1, 58.59.60.61 Host(A), subdomain2, 58.59.60.61 My router is a pfSense box. It forwards all port 80 traffic to a group alias called "WebServers," which is my 3 web server IP's. This setup should work right? I believe I need to set the "host header names" in my web servers. In IIS I know how to do this. How do I do this in Apache2?

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• Win 2003 STD network adapter always showing DHCP when in static IP configuration, + it loses the DNS

  - by Darragh

  Hi, I have a server that after the first configuration it was DHCP, now I have added it to our domain and in a static IP, however after a few moments it returns to DHCP but with only some of the IPv4 setting staying the same, It loses DNS for example. I'm not sure what is causing the problem but all I know is this started to happen after I added it to the domain, Would it be a domain policy? or the NIC drivers Spec; Dell M605 Blade server Windows 2003 STD SP1 Intel Xeon Quad core NIC: Dual embedded Broadcom NetXtreme IITM 5708 Gigabit Ethernet NIC w/ TOE

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• Systemd-networkd: How can I prepend a static nameserver entry to DHCP-discovered nameservers?

  - by runiq

  I'm using systemd 213 on Arch Linux, and systemd-networkd with DHCP to connect to the internet. I'm also running a caching DNS server on 127.0.0.1. I'd like to make this server the first DNS server in the list, but I'd also like to use the nameservers discovered by systemd-networkd's DHCP facility. Using a static resolv.conf isn't really possible, because I connect to networks with different DNS settings. I know I can set fallback DNS servers in /etc/systemd/resolved.conf, but is there a way with systemd-networkd to prepend my local DNS server to those discovered by DHCP?

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• Can I use static routing to allow me to use my public IP from my LAN?

  - by jnm2

  I would like to be able to use the same hostname to connect to my computer from my phone whether I'm at home or away. Currently I have to maintain duplicate entries for remote desktop, for instance. My router doesn't seem to have a NAT loopback option. I have two routers in fact, a cable modem which goes straight to my main router which does wireless. I can add to the static routing tables on each. Can I use this to loopback the public IP or do I need different routers?

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• Is is better to combine Apache for file manipulation and upload and Nginx for static file serving, or to use one of the two alone

  - by user1032393

  Based on my research, I've read that nginx is best and ideal for serving up static files and images. My application depends heavily on uploading of images and rewriting them, then serving them up. Given that I only have one VPS currently, it has been suggested that I use nginx to serve up the images and website, and reverse proxy to Apache (on the same VPS) to rewrite files with image magick and handle the file uploads. Which would be the best solution, Apache, Nginx, or Apache + Nginx? In terms of best solution, I'm looking at minimal average RAM consumption, while maintaining decent load speed of maybe sub 2 seconds?

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• How to stop Nginx sending static file requests to the CakePHP app controller when running Cake in a subdirectory?

  - by robotmay

  I'm trying to run a CakePHP app from within a subfolder on Nginx, but the static files are not being found and are instead being passed to the app controller. Here's my current config: location /uniquetv { index index.php index.html; if (-f $request_filename) { break; } if (!-e $request_filename) { rewrite ^/uniquetv(.+)$ /uniquetv/webroot/$1 last; break; } } location /uniquetv/webroot { index index.php; if (!-e $request_filename) { rewrite ^/uniquetv/webroot/(.+)$ /uniquetv/webroot/index.php?url=$1 last; break; } } Any ideas? :)

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• What are the typical methods used to scale up/out email storage servers?

  - by nareshov

  Hi, What I've tried: I have two email storage architectures. Old and new. Old: courier-imapds on several (18+) 1TB-storage servers. If one of them show signs of running out of disk space, we migrate a few email accounts to another server. the servers don't have replicas. no backups either. New: dovecot2 on a single huge server with 16TB (SATA) storage and a few SSDs we store fresh mails on the SSDs and run a doveadm purge to move mails older than a day to the SATA disks there is an identical server which has a max-15min-old rsync backup from the primary server higher-ups/management wanted to pack in as much storage as possible per server in order to minimise the cost of SSDs per server the rsync'ing is done because GlusterFS wasn't replicating well under that high small/random-IO. scaling out was expected to be done with provisioning another pair of such huge servers on facing disk-crunch issues like in the old architecture, manual moving of email accounts would be done. Concerns/doubts: I'm not convinced with the synchronously-replicated filesystem idea works well for heavy random/small-IO. GlusterFS isn't working for us yet, I'm not sure if there's another filesystem out there for this use case. The idea was to keep identical pairs and use DNS round-robin for email delivery and IMAP/POP3 access. And if one the servers went down for whatever reasons (planned/unplanned), we'd move the IP to the other server in the pair. In filesystems like Lustre, I get the advantage of a single namespace whereby I do not have to worry about manually migrating accounts around and updating MAILHOME paths and other metadata/data. Questions: What are the typical methods used to scale up/out with the traditional software (courier-imapd / dovecot)? Do traditional software that store on a locally mounted filesystem pose a roadblock to scale out with minimal "problems"? Does one have to re-write (parts of) these to work with an object-storage of some sort - such as OpenStack object storage?

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• Java: repetition, overuse -- problem?

  - by HH

  I try to be as minimalist as possible. Repetition is a problem. I hate it. When is it really a problem? what is static-overuse? what is field-method overuse? what is class-overuse? are there more types of overuse? Problem A: when it is too much to use of static? private static class Data { private static String fileContent; private static SizeSequence lineMap; private static File fileThing; private static char type; private static boolean binary; private static String name; private static String path; } private static class Print { //<1st LINE, LEFT_SIDE, 2nd LINE, RIGHT_SIDE> private Integer[] printPositions=new Integer[4]; private static String fingerPrint; private static String formatPrint; } Problem B: when it is too much to get field data with private methods? public Stack<Integer> getPositions(){return positions;} public Integer[] getPrintPositions(){return printPositions;} private Stack<String> getPrintViews(){return printViews;} private Stack<String> getPrintViewsPerFile(){return printViewsPerFile;} public String getPrintView(){return printView;} public String getFingerPrint(){return fingerPrint;} public String getFormatPrint(){return formatPrint;} public String getFileContent(){return fileContent;} public SizeSequence getLineMap(){return lineMap;} public File getFile(){return fileThing;} public boolean getBinary(){return binary;} public char getType(){return type;} public String getPath(){return path;} public FileObject getData(){return fObj;} public String getSearchTerm(){return searchTerm;} Related interface overuse overuse of static in a Game

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• An Introduction to ASP.NET Web API

  - by Rick Strahl

  Microsoft recently released ASP.NET MVC 4.0 and .NET 4.5 and along with it, the brand spanking new ASP.NET Web API. Web API is an exciting new addition to the ASP.NET stack that provides a new, well-designed HTTP framework for creating REST and AJAX APIs (API is Microsoft’s new jargon for a service, in case you’re wondering). Although Web API ships and installs with ASP.NET MVC 4, you can use Web API functionality in any ASP.NET project, including WebForms, WebPages and MVC or just a Web API by itself. And you can also self-host Web API in your own applications from Console, Desktop or Service applications. If you're interested in a high level overview on what ASP.NET Web API is and how it fits into the ASP.NET stack you can check out my previous post: Where does ASP.NET Web API fit? In the following article, I'll focus on a practical, by example introduction to ASP.NET Web API. All the code discussed in this article is available in GitHub: https://github.com/RickStrahl/AspNetWebApiArticle [republished from my Code Magazine Article and updated for RTM release of ASP.NET Web API] Getting Started To start I’ll create a new empty ASP.NET application to demonstrate that Web API can work with any kind of ASP.NET project. Although you can create a new project based on the ASP.NET MVC/Web API template to quickly get up and running, I’ll take you through the manual setup process, because one common use case is to add Web API functionality to an existing ASP.NET application. This process describes the steps needed to hook up Web API to any ASP.NET 4.0 application. Start by creating an ASP.NET Empty Project. Then create a new folder in the project called Controllers. Add a Web API Controller Class Once you have any kind of ASP.NET project open, you can add a Web API Controller class to it. Web API Controllers are very similar to MVC Controller classes, but they work in any kind of project. Add a new item to this folder by using the Add New Item option in Visual Studio and choose Web API Controller Class, as shown in Figure 1. Figure 1: This is how you create a new Controller Class in Visual Studio   Make sure that the name of the controller class includes Controller at the end of it, which is required in order for Web API routing to find it. Here, the name for the class is AlbumApiController. For this example, I’ll use a Music Album model to demonstrate basic behavior of Web API. The model consists of albums and related songs where an album has properties like Name, Artist and YearReleased and a list of songs with a SongName and SongLength as well as an AlbumId that links it to the album. You can find the code for the model (and the rest of these samples) on Github. To add the file manually, create a new folder called Model, and add a new class Album.cs and copy the code into it. There’s a static AlbumData class with a static CreateSampleAlbumData() method that creates a short list of albums on a static .Current that I’ll use for the examples. Before we look at what goes into the controller class though, let’s hook up routing so we can access this new controller. Hooking up Routing in Global.asax To start, I need to perform the one required configuration task in order for Web API to work: I need to configure routing to the controller. Like MVC, Web API uses routing to provide clean, extension-less URLs to controller methods. Using an extension method to ASP.NET’s static RouteTable class, you can use the MapHttpRoute() (in the System.Web.Http namespace) method to hook-up the routing during Application_Start in global.asax.cs shown in Listing 1.using System; using System.Web.Routing; using System.Web.Http; namespace AspNetWebApi { public class Global : System.Web.HttpApplication { protected void Application_Start(object sender, EventArgs e) { RouteTable.Routes.MapHttpRoute( name: "AlbumVerbs", routeTemplate: "albums/{title}", defaults: new { symbol = RouteParameter.Optional, controller="AlbumApi" } ); } } } This route configures Web API to direct URLs that start with an albums folder to the AlbumApiController class. Routing in ASP.NET is used to create extensionless URLs and allows you to map segments of the URL to specific Route Value parameters. A route parameter, with a name inside curly brackets like {name}, is mapped to parameters on the controller methods. Route parameters can be optional, and there are two special route parameters – controller and action – that determine the controller to call and the method to activate respectively. HTTP Verb Routing Routing in Web API can route requests by HTTP Verb in addition to standard {controller},{action} routing. For the first examples, I use HTTP Verb routing, as shown Listing 1. Notice that the route I’ve defined does not include an {action} route value or action value in the defaults. Rather, Web API can use the HTTP Verb in this route to determine the method to call the controller, and a GET request maps to any method that starts with Get. So methods called Get() or GetAlbums() are matched by a GET request and a POST request maps to a Post() or PostAlbum(). Web API matches a method by name and parameter signature to match a route, query string or POST values. In lieu of the method name, the [HttpGet,HttpPost,HttpPut,HttpDelete, etc] attributes can also be used to designate the accepted verbs explicitly if you don’t want to follow the verb naming conventions. Although HTTP Verb routing is a good practice for REST style resource APIs, it’s not required and you can still use more traditional routes with an explicit {action} route parameter. When {action} is supplied, the HTTP verb routing is ignored. I’ll talk more about alternate routes later. When you’re finished with initial creation of files, your project should look like Figure 2.   Figure 2: The initial project has the new API Controller Album model   Creating a small Album Model Now it’s time to create some controller methods to serve data. For these examples, I’ll use a very simple Album and Songs model to play with, as shown in Listing 2. public class Song { public string AlbumId { get; set; } [Required, StringLength(80)] public string SongName { get; set; } [StringLength(5)] public string SongLength { get; set; } } public class Album { public string Id { get; set; } [Required, StringLength(80)] public string AlbumName { get; set; } [StringLength(80)] public string Artist { get; set; } public int YearReleased { get; set; } public DateTime Entered { get; set; } [StringLength(150)] public string AlbumImageUrl { get; set; } [StringLength(200)] public string AmazonUrl { get; set; } public virtual List<Song> Songs { get; set; } public Album() { Songs = new List<Song>(); Entered = DateTime.Now; // Poor man's unique Id off GUID hash Id = Guid.NewGuid().GetHashCode().ToString("x"); } public void AddSong(string songName, string songLength = null) { this.Songs.Add(new Song() { AlbumId = this.Id, SongName = songName, SongLength = songLength }); } } Once the model has been created, I also added an AlbumData class that generates some static data in memory that is loaded onto a static .Current member. The signature of this class looks like this and that's what I'll access to retrieve the base data:public static class AlbumData { // sample data - static list public static List<Album> Current = CreateSampleAlbumData(); /// <summary> /// Create some sample data /// </summary> /// <returns></returns> public static List<Album> CreateSampleAlbumData() { … }} You can check out the full code for the data generation online. Creating an AlbumApiController Web API shares many concepts of ASP.NET MVC, and the implementation of your API logic is done by implementing a subclass of the System.Web.Http.ApiController class. Each public method in the implemented controller is a potential endpoint for the HTTP API, as long as a matching route can be found to invoke it. The class name you create should end in Controller, which is how Web API matches the controller route value to figure out which class to invoke. Inside the controller you can implement methods that take standard .NET input parameters and return .NET values as results. Web API’s binding tries to match POST data, route values, form values or query string values to your parameters. Because the controller is configured for HTTP Verb based routing (no {action} parameter in the route), any methods that start with Getxxxx() are called by an HTTP GET operation. You can have multiple methods that match each HTTP Verb as long as the parameter signatures are different and can be matched by Web API. In Listing 3, I create an AlbumApiController with two methods to retrieve a list of albums and a single album by its title .public class AlbumApiController : ApiController { public IEnumerable<Album> GetAlbums() { var albums = AlbumData.Current.OrderBy(alb => alb.Artist); return albums; } public Album GetAlbum(string title) { var album = AlbumData.Current .SingleOrDefault(alb => alb.AlbumName.Contains(title)); return album; }} To access the first two requests, you can use the following URLs in your browser: http://localhost/aspnetWebApi/albumshttp://localhost/aspnetWebApi/albums/Dirty%20Deeds Note that you’re not specifying the actions of GetAlbum or GetAlbums in these URLs. Instead Web API’s routing uses HTTP GET verb to route to these methods that start with Getxxx() with the first mapping to the parameterless GetAlbums() method and the latter to the GetAlbum(title) method that receives the title parameter mapped as optional in the route. Content Negotiation When you access any of the URLs above from a browser, you get either an XML or JSON result returned back. The album list result for Chrome 17 and Internet Explorer 9 is shown Figure 3. Figure 3: Web API responses can vary depending on the browser used, demonstrating Content Negotiation in action as these two browsers send different HTTP Accept headers.   Notice that the results are not the same: Chrome returns an XML response and IE9 returns a JSON response. Whoa, what’s going on here? Shouldn’t we see the same result in both browsers? Actually, no. Web API determines what type of content to return based on Accept headers. HTTP clients, like browsers, use Accept headers to specify what kind of content they’d like to see returned. Browsers generally ask for HTML first, followed by a few additional content types. Chrome (and most other major browsers) ask for: Accept: text/html, application/xhtml+xml,application/xml; q=0.9,*/*;q=0.8 IE9 asks for: Accept: text/html, application/xhtml+xml, */* Note that Chrome’s Accept header includes application/xml, which Web API finds in its list of supported media types and returns an XML response. IE9 does not include an Accept header type that works on Web API by default, and so it returns the default format, which is JSON. This is an important and very useful feature that was missing from any previous Microsoft REST tools: Web API automatically switches output formats based on HTTP Accept headers. Nowhere in the server code above do you have to explicitly specify the output format. Rather, Web API determines what format the client is requesting based on the Accept headers and automatically returns the result based on the available formatters. This means that a single method can handle both XML and JSON results.. Using this simple approach makes it very easy to create a single controller method that can return JSON, XML, ATOM or even OData feeds by providing the appropriate Accept header from the client. By default you don’t have to worry about the output format in your code. Note that you can still specify an explicit output format if you choose, either globally by overriding the installed formatters, or individually by returning a lower level HttpResponseMessage instance and setting the formatter explicitly. More on that in a minute. Along the same lines, any content sent to the server via POST/PUT is parsed by Web API based on the HTTP Content-type of the data sent. The same formats allowed for output are also allowed on input. Again, you don’t have to do anything in your code – Web API automatically performs the deserialization from the content. Accessing Web API JSON Data with jQuery A very common scenario for Web API endpoints is to retrieve data for AJAX calls from the Web browser. Because JSON is the default format for Web API, it’s easy to access data from the server using jQuery and its getJSON() method. This example receives the albums array from GetAlbums() and databinds it into the page using knockout.js.$.getJSON("albums/", function (albums) { // make knockout template visible $(".album").show(); // create view object and attach array var view = { albums: albums }; ko.applyBindings(view); }); Figure 4 shows this and the next example’s HTML output. You can check out the complete HTML and script code at http://goo.gl/Ix33C (.html) and http://goo.gl/tETlg (.js). Figu Figure 4: The Album Display sample uses JSON data loaded from Web API.   The result from the getJSON() call is a JavaScript object of the server result, which comes back as a JavaScript array. In the code, I use knockout.js to bind this array into the UI, which as you can see, requires very little code, instead using knockout’s data-bind attributes to bind server data to the UI. Of course, this is just one way to use the data – it’s entirely up to you to decide what to do with the data in your client code. Along the same lines, I can retrieve a single album to display when the user clicks on an album. The response returns the album information and a child array with all the songs. The code to do this is very similar to the last example where we pulled the albums array:$(".albumlink").live("click", function () { var id = $(this).data("id"); // title $.getJSON("albums/" + id, function (album) { ko.applyBindings(album, $("#divAlbumDialog")[0]); $("#divAlbumDialog").show(); }); }); Here the URL looks like this: /albums/Dirty%20Deeds, where the title is the ID captured from the clicked element’s data ID attribute. Explicitly Overriding Output Format When Web API automatically converts output using content negotiation, it does so by matching Accept header media types to the GlobalConfiguration.Configuration.Formatters and the SupportedMediaTypes of each individual formatter. You can add and remove formatters to globally affect what formats are available and it’s easy to create and plug in custom formatters.The example project includes a JSONP formatter that can be plugged in to provide JSONP support for requests that have a callback= querystring parameter. Adding, removing or replacing formatters is a global option you can use to manipulate content. It’s beyond the scope of this introduction to show how it works, but you can review the sample code or check out my blog entry on the subject (http://goo.gl/UAzaR). If automatic processing is not desirable in a particular Controller method, you can override the response output explicitly by returning an HttpResponseMessage instance. HttpResponseMessage is similar to ActionResult in ASP.NET MVC in that it’s a common way to return an abstract result message that contains content. HttpResponseMessage s parsed by the Web API framework using standard interfaces to retrieve the response data, status code, headers and so on[MS2] . Web API turns every response – including those Controller methods that return static results – into HttpResponseMessage instances. Explicitly returning an HttpResponseMessage instance gives you full control over the output and lets you mostly bypass WebAPI’s post-processing of the HTTP response on your behalf. HttpResponseMessage allows you to customize the response in great detail. Web API’s attention to detail in the HTTP spec really shows; many HTTP options are exposed as properties and enumerations with detailed IntelliSense comments. Even if you’re new to building REST-based interfaces, the API guides you in the right direction for returning valid responses and response codes. For example, assume that I always want to return JSON from the GetAlbums() controller method and ignore the default media type content negotiation. To do this, I can adjust the output format and headers as shown in Listing 4.public HttpResponseMessage GetAlbums() { var albums = AlbumData.Current.OrderBy(alb => alb.Artist); // Create a new HttpResponse with Json Formatter explicitly var resp = new HttpResponseMessage(HttpStatusCode.OK); resp.Content = new ObjectContent<IEnumerable<Album>>( albums, new JsonMediaTypeFormatter()); // Get Default Formatter based on Content Negotiation //var resp = Request.CreateResponse<IEnumerable<Album>>(HttpStatusCode.OK, albums); resp.Headers.ConnectionClose = true; resp.Headers.CacheControl = new CacheControlHeaderValue(); resp.Headers.CacheControl.Public = true; return resp; } This example returns the same IEnumerable<Album> value, but it wraps the response into an HttpResponseMessage so you can control the entire HTTP message result including the headers, formatter and status code. In Listing 4, I explicitly specify the formatter using the JsonMediaTypeFormatter to always force the content to JSON.  If you prefer to use the default content negotiation with HttpResponseMessage results, you can create the Response instance using the Request.CreateResponse method:var resp = Request.CreateResponse<IEnumerable<Album>>(HttpStatusCode.OK, albums); This provides you an HttpResponse object that's pre-configured with the default formatter based on Content Negotiation. Once you have an HttpResponse object you can easily control most HTTP aspects on this object. What's sweet here is that there are many more detailed properties on HttpResponse than the core ASP.NET Response object, with most options being explicitly configurable with enumerations that make it easy to pick the right headers and response codes from a list of valid codes. It makes HTTP features available much more discoverable even for non-hardcore REST/HTTP geeks. Non-Serialized Results The output returned doesn’t have to be a serialized value but can also be raw data, like strings, binary data or streams. You can use the HttpResponseMessage.Content object to set a number of common Content classes. Listing 5 shows how to return a binary image using the ByteArrayContent class from a Controller method. [HttpGet] public HttpResponseMessage AlbumArt(string title) { var album = AlbumData.Current.FirstOrDefault(abl => abl.AlbumName.StartsWith(title)); if (album == null) { var resp = Request.CreateResponse<ApiMessageError>( HttpStatusCode.NotFound, new ApiMessageError("Album not found")); return resp; } // kinda silly - we would normally serve this directly // but hey - it's a demo. var http = new WebClient(); var imageData = http.DownloadData(album.AlbumImageUrl); // create response and return var result = new HttpResponseMessage(HttpStatusCode.OK); result.Content = new ByteArrayContent(imageData); result.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpeg"); return result; } The image retrieval from Amazon is contrived, but it shows how to return binary data using ByteArrayContent. It also demonstrates that you can easily return multiple types of content from a single controller method, which is actually quite common. If an error occurs - such as a resource can’t be found or a validation error – you can return an error response to the client that’s very specific to the error. In GetAlbumArt(), if the album can’t be found, we want to return a 404 Not Found status (and realistically no error, as it’s an image). Note that if you are not using HTTP Verb-based routing or not accessing a method that starts with Get/Post etc., you have to specify one or more HTTP Verb attributes on the method explicitly. Here, I used the [HttpGet] attribute to serve the image. Another option to handle the error could be to return a fixed placeholder image if no album could be matched or the album doesn’t have an image. When returning an error code, you can also return a strongly typed response to the client. For example, you can set the 404 status code and also return a custom error object (ApiMessageError is a class I defined) like this:return Request.CreateResponse<ApiMessageError>( HttpStatusCode.NotFound, new ApiMessageError("Album not found") );   If the album can be found, the image will be returned. The image is downloaded into a byte[] array, and then assigned to the result’s Content property. I created a new ByteArrayContent instance and assigned the image’s bytes and the content type so that it displays properly in the browser. There are other content classes available: StringContent, StreamContent, ByteArrayContent, MultipartContent, and ObjectContent are at your disposal to return just about any kind of content. You can create your own Content classes if you frequently return custom types and handle the default formatter assignments that should be used to send the data out . Although HttpResponseMessage results require more code than returning a plain .NET value from a method, it allows much more control over the actual HTTP processing than automatic processing. It also makes it much easier to test your controller methods as you get a response object that you can check for specific status codes and output messages rather than just a result value. Routing Again Ok, let’s get back to the image example. Using the original routing we have setup using HTTP Verb routing there's no good way to serve the image. In order to return my album art image I’d like to use a URL like this: http://localhost/aspnetWebApi/albums/Dirty%20Deeds/image In order to create a URL like this, I have to create a new Controller because my earlier routes pointed to the AlbumApiController using HTTP Verb routing. HTTP Verb based routing is great for representing a single set of resources such as albums. You can map operations like add, delete, update and read easily using HTTP Verbs. But you cannot mix action based routing into a an HTTP Verb routing controller - you can only map HTTP Verbs and each method has to be unique based on parameter signature. You can't have multiple GET operations to methods with the same signature. So GetImage(string id) and GetAlbum(string title) are in conflict in an HTTP GET routing scenario. In fact, I was unable to make the above Image URL work with any combination of HTTP Verb plus Custom routing using the single Albums controller. There are number of ways around this, but all involve additional controllers.  Personally, I think it’s easier to use explicit Action routing and then add custom routes if you need to simplify your URLs further. So in order to accommodate some of the other examples, I created another controller – AlbumRpcApiController – to handle all requests that are explicitly routed via actions (/albums/rpc/AlbumArt) or are custom routed with explicit routes defined in the HttpConfiguration. I added the AlbumArt() method to this new AlbumRpcApiController class. For the image URL to work with the new AlbumRpcApiController, you need a custom route placed before the default route from Listing 1.RouteTable.Routes.MapHttpRoute( name: "AlbumRpcApiAction", routeTemplate: "albums/rpc/{action}/{title}", defaults: new { title = RouteParameter.Optional, controller = "AlbumRpcApi", action = "GetAblums" } ); Now I can use either of the following URLs to access the image: Custom route: (/albums/rpc/{title}/image)http://localhost/aspnetWebApi/albums/PowerAge/image Action route: (/albums/rpc/action/{title})http://localhost/aspnetWebAPI/albums/rpc/albumart/PowerAge Sending Data to the Server To send data to the server and add a new album, you can use an HTTP POST operation. Since I’m using HTTP Verb-based routing in the original AlbumApiController, I can implement a method called PostAlbum()to accept a new album from the client. Listing 6 shows the Web API code to add a new album.public HttpResponseMessage PostAlbum(Album album) { if (!this.ModelState.IsValid) { // my custom error class var error = new ApiMessageError() { message = "Model is invalid" }; // add errors into our client error model for client foreach (var prop in ModelState.Values) { var modelError = prop.Errors.FirstOrDefault(); if (!string.IsNullOrEmpty(modelError.ErrorMessage)) error.errors.Add(modelError.ErrorMessage); else error.errors.Add(modelError.Exception.Message); } return Request.CreateResponse<ApiMessageError>(HttpStatusCode.Conflict, error); } // update song id which isn't provided foreach (var song in album.Songs) song.AlbumId = album.Id; // see if album exists already var matchedAlbum = AlbumData.Current .SingleOrDefault(alb => alb.Id == album.Id || alb.AlbumName == album.AlbumName); if (matchedAlbum == null) AlbumData.Current.Add(album); else matchedAlbum = album; // return a string to show that the value got here var resp = Request.CreateResponse(HttpStatusCode.OK, string.Empty); resp.Content = new StringContent(album.AlbumName + " " + album.Entered.ToString(), Encoding.UTF8, "text/plain"); return resp; } The PostAlbum() method receives an album parameter, which is automatically deserialized from the POST buffer the client sent. The data passed from the client can be either XML or JSON. Web API automatically figures out what format it needs to deserialize based on the content type and binds the content to the album object. Web API uses model binding to bind the request content to the parameter(s) of controller methods. Like MVC you can check the model by looking at ModelState.IsValid. If it’s not valid, you can run through the ModelState.Values collection and check each binding for errors. Here I collect the error messages into a string array that gets passed back to the client via the result ApiErrorMessage object. When a binding error occurs, you’ll want to return an HTTP error response and it’s best to do that with an HttpResponseMessage result. In Listing 6, I used a custom error class that holds a message and an array of detailed error messages for each binding error. I used this object as the content to return to the client along with my Conflict HTTP Status Code response. If binding succeeds, the example returns a string with the name and date entered to demonstrate that you captured the data. Normally, a method like this should return a Boolean or no response at all (HttpStatusCode.NoConent). The sample uses a simple static list to hold albums, so once you’ve added the album using the Post operation, you can hit the /albums/ URL to see that the new album was added. The client jQuery code to call the POST operation from the client with jQuery is shown in Listing 7. var id = new Date().getTime().toString(); var album = { "Id": id, "AlbumName": "Power Age", "Artist": "AC/DC", "YearReleased": 1977, "Entered": "2002-03-11T18:24:43.5580794-10:00", "AlbumImageUrl": http://ecx.images-amazon.com/images/…, "AmazonUrl": http://www.amazon.com/…, "Songs": [ { "SongName": "Rock 'n Roll Damnation", "SongLength": 3.12}, { "SongName": "Downpayment Blues", "SongLength": 4.22 }, { "SongName": "Riff Raff", "SongLength": 2.42 } ] } $.ajax( { url: "albums/", type: "POST", contentType: "application/json", data: JSON.stringify(album), processData: false, beforeSend: function (xhr) { // not required since JSON is default output xhr.setRequestHeader("Accept", "application/json"); }, success: function (result) { // reload list of albums page.loadAlbums(); }, error: function (xhr, status, p3, p4) { var err = "Error"; if (xhr.responseText && xhr.responseText[0] == "{") err = JSON.parse(xhr.responseText).message; alert(err); } }); The code in Listing 7 creates an album object in JavaScript to match the structure of the .NET Album class. This object is passed to the $.ajax() function to send to the server as POST. The data is turned into JSON and the content type set to application/json so that the server knows what to convert when deserializing in the Album instance. The jQuery code hooks up success and failure events. Success returns the result data, which is a string that’s echoed back with an alert box. If an error occurs, jQuery returns the XHR instance and status code. You can check the XHR to see if a JSON object is embedded and if it is, you can extract it by de-serializing it and accessing the .message property. REST standards suggest that updates to existing resources should use PUT operations. REST standards aside, I’m not a big fan of separating out inserts and updates so I tend to have a single method that handles both. But if you want to follow REST suggestions, you can create a PUT method that handles updates by forwarding the PUT operation to the POST method:public HttpResponseMessage PutAlbum(Album album) { return PostAlbum(album); } To make the corresponding $.ajax() call, all you have to change from Listing 7 is the type: from POST to PUT. Model Binding with UrlEncoded POST Variables In the example in Listing 7 I used JSON objects to post a serialized object to a server method that accepted an strongly typed object with the same structure, which is a common way to send data to the server. However, Web API supports a number of different ways that data can be received by server methods. For example, another common way is to use plain UrlEncoded POST  values to send to the server. Web API supports Model Binding that works similar (but not the same) as MVC's model binding where POST variables are mapped to properties of object parameters of the target method. This is actually quite common for AJAX calls that want to avoid serialization and the potential requirement of a JSON parser on older browsers. For example, using jQUery you might use the $.post() method to send a new album to the server (albeit one without songs) using code like the following:$.post("albums/",{AlbumName: "Dirty Deeds", YearReleased: 1976 … },albumPostCallback); Although the code looks very similar to the client code we used before passing JSON, here the data passed is URL encoded values (AlbumName=Dirty+Deeds&YearReleased=1976 etc.). Web API then takes this POST data and maps each of the POST values to the properties of the Album object in the method's parameter. Although the client code is different the server can both handle the JSON object, or the UrlEncoded POST values. Dynamic Access to POST Data There are also a few options available to dynamically access POST data, if you know what type of data you're dealing with. If you have POST UrlEncoded values, you can dynamically using a FormsDataCollection:[HttpPost] public string PostAlbum(FormDataCollection form) { return string.Format("{0} - released {1}", form.Get("AlbumName"),form.Get("RearReleased")); } The FormDataCollection is a very simple object, that essentially provides the same functionality as Request.Form[] in ASP.NET. Request.Form[] still works if you're running hosted in an ASP.NET application. However as a general rule, while ASP.NET's functionality is always available when running Web API hosted inside of an  ASP.NET application, using the built in classes specific to Web API makes it possible to run Web API applications in a self hosted environment outside of ASP.NET. If your client is sending JSON to your server, and you don't want to map the JSON to a strongly typed object because you only want to retrieve a few simple values, you can also accept a JObject parameter in your API methods:[HttpPost] public string PostAlbum(JObject jsonData) { dynamic json = jsonData; JObject jalbum = json.Album; JObject juser = json.User; string token = json.UserToken; var album = jalbum.ToObject<Album>(); var user = juser.ToObject<User>(); return String.Format("{0} {1} {2}", album.AlbumName, user.Name, token); } There quite a few options available to you to receive data with Web API, which gives you more choices for the right tool for the job. Unfortunately one shortcoming of Web API is that POST data is always mapped to a single parameter. This means you can't pass multiple POST parameters to methods that receive POST data. It's possible to accept multiple parameters, but only one can map to the POST content - the others have to come from the query string or route values. I have a couple of Blog POSTs that explain what works and what doesn't here: Passing multiple POST parameters to Web API Controller Methods Mapping UrlEncoded POST Values in ASP.NET Web API   Handling Delete Operations Finally, to round out the server API code of the album example we've been discussin, here’s the DELETE verb controller method that allows removal of an album by its title:public HttpResponseMessage DeleteAlbum(string title) { var matchedAlbum = AlbumData.Current.Where(alb => alb.AlbumName == title) .SingleOrDefault(); if (matchedAlbum == null) return new HttpResponseMessage(HttpStatusCode.NotFound); AlbumData.Current.Remove(matchedAlbum); return new HttpResponseMessage(HttpStatusCode.NoContent); } To call this action method using jQuery, you can use:$(".removeimage").live("click", function () { var $el = $(this).parent(".album"); var txt = $el.find("a").text(); $.ajax({ url: "albums/" + encodeURIComponent(txt), type: "Delete", success: function (result) { $el.fadeOut().remove(); }, error: jqError }); }   Note the use of the DELETE verb in the $.ajax() call, which routes to DeleteAlbum on the server. DELETE is a non-content operation, so you supply a resource ID (the title) via route value or the querystring. Routing Conflicts In all requests with the exception of the AlbumArt image example shown so far, I used HTTP Verb routing that I set up in Listing 1. HTTP Verb Routing is a recommendation that is in line with typical REST access to HTTP resources. However, it takes quite a bit of effort to create REST-compliant API implementations based only on HTTP Verb routing only. You saw one example that didn’t really fit – the return of an image where I created a custom route albums/{title}/image that required creation of a second controller and a custom route to work. HTTP Verb routing to a controller does not mix with custom or action routing to the same controller because of the limited mapping of HTTP verbs imposed by HTTP Verb routing. To understand some of the problems with verb routing, let’s look at another example. Let’s say you create a GetSortableAlbums() method like this and add it to the original AlbumApiController accessed via HTTP Verb routing:[HttpGet] public IQueryable<Album> SortableAlbums() { var albums = AlbumData.Current; // generally should be done only on actual queryable results (EF etc.) // Done here because we're running with a static list but otherwise might be slow return albums.AsQueryable(); } If you compile this code and try to now access the /albums/ link, you get an error: Multiple Actions were found that match the request. HTTP Verb routing only allows access to one GET operation per parameter/route value match. If more than one method exists with the same parameter signature, it doesn’t work. As I mentioned earlier for the image display, the only solution to get this method to work is to throw it into another controller. Because I already set up the AlbumRpcApiController I can add the method there. First, I should rename the method to SortableAlbums() so I’m not using a Get prefix for the method. This also makes the action parameter look cleaner in the URL - it looks less like a method and more like a noun. I can then create a new route that handles direct-action mapping:RouteTable.Routes.MapHttpRoute( name: "AlbumRpcApiAction", routeTemplate: "albums/rpc/{action}/{title}", defaults: new { title = RouteParameter.Optional, controller = "AlbumRpcApi", action = "GetAblums" } ); As I am explicitly adding a route segment – rpc – into the route template, I can now reference explicit methods in the Web API controller using URLs like this: http://localhost/AspNetWebApi/rpc/SortableAlbums Error Handling I’ve already done some minimal error handling in the examples. For example in Listing 6, I detected some known-error scenarios like model validation failing or a resource not being found and returning an appropriate HttpResponseMessage result. But what happens if your code just blows up or causes an exception? If you have a controller method, like this:[HttpGet] public void ThrowException() { throw new UnauthorizedAccessException("Unauthorized Access Sucka"); } You can call it with this: http://localhost/AspNetWebApi/albums/rpc/ThrowException The default exception handling displays a 500-status response with the serialized exception on the local computer only. When you connect from a remote computer, Web API throws back a 500  HTTP Error with no data returned (IIS then adds its HTML error page). The behavior is configurable in the GlobalConfiguration:GlobalConfiguration .Configuration .IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Never; If you want more control over your error responses sent from code, you can throw explicit error responses yourself using HttpResponseException. When you throw an HttpResponseException the response parameter is used to generate the output for the Controller action. [HttpGet] public void ThrowError() { var resp = Request.CreateResponse<ApiMessageError>( HttpStatusCode.BadRequest, new ApiMessageError("Your code stinks!")); throw new HttpResponseException(resp); } Throwing an HttpResponseException stops the processing of the controller method and immediately returns the response you passed to the exception. Unlike other Exceptions fired inside of WebAPI, HttpResponseException bypasses the Exception Filters installed and instead just outputs the response you provide. In this case, the serialized ApiMessageError result string is returned in the default serialization format – XML or JSON. You can pass any content to HttpResponseMessage, which includes creating your own exception objects and consistently returning error messages to the client. Here’s a small helper method on the controller that you might use to send exception info back to the client consistently:private void ThrowSafeException(string message, HttpStatusCode statusCode = HttpStatusCode.BadRequest) { var errResponse = Request.CreateResponse<ApiMessageError>(statusCode, new ApiMessageError() { message = message }); throw new HttpResponseException(errResponse); } You can then use it to output any captured errors from code:[HttpGet] public void ThrowErrorSafe() { try { List<string> list = null; list.Add("Rick"); } catch (Exception ex) { ThrowSafeException(ex.Message); } }   Exception Filters Another more global solution is to create an Exception Filter. Filters in Web API provide the ability to pre- and post-process controller method operations. An exception filter looks at all exceptions fired and then optionally creates an HttpResponseMessage result. Listing 8 shows an example of a basic Exception filter implementation.public class UnhandledExceptionFilter : ExceptionFilterAttribute { public override void OnException(HttpActionExecutedContext context) { HttpStatusCode status = HttpStatusCode.InternalServerError; var exType = context.Exception.GetType(); if (exType == typeof(UnauthorizedAccessException)) status = HttpStatusCode.Unauthorized; else if (exType == typeof(ArgumentException)) status = HttpStatusCode.NotFound; var apiError = new ApiMessageError() { message = context.Exception.Message }; // create a new response and attach our ApiError object // which now gets returned on ANY exception result var errorResponse = context.Request.CreateResponse<ApiMessageError>(status, apiError); context.Response = errorResponse; base.OnException(context); } } Exception Filter Attributes can be assigned to an ApiController class like this:[UnhandledExceptionFilter] public class AlbumRpcApiController : ApiController or you can globally assign it to all controllers by adding it to the HTTP Configuration's Filters collection:GlobalConfiguration.Configuration.Filters.Add(new UnhandledExceptionFilter()); The latter is a great way to get global error trapping so that all errors (short of hard IIS errors and explicit HttpResponseException errors) return a valid error response that includes error information in the form of a known-error object. Using a filter like this allows you to throw an exception as you normally would and have your filter create a response in the appropriate output format that the client expects. For example, an AJAX application can on failure expect to see a JSON error result that corresponds to the real error that occurred rather than a 500 error along with HTML error page that IIS throws up. You can even create some custom exceptions so you can differentiate your own exceptions from unhandled system exceptions - you often don't want to display error information from 'unknown' exceptions as they may contain sensitive system information or info that's not generally useful to users of your application/site. This is just one example of how ASP.NET Web API is configurable and extensible. Exception filters are just one example of how you can plug-in into the Web API request flow to modify output. Many more hooks exist and I’ll take a closer look at extensibility in Part 2 of this article in the future. Summary Web API is a big improvement over previous Microsoft REST and AJAX toolkits. The key features to its usefulness are its ease of use with simple controller based logic, familiar MVC-style routing, low configuration impact, extensibility at all levels and tight attention to exposing and making HTTP semantics easily discoverable and easy to use. Although none of the concepts used in Web API are new or radical, Web API combines the best of previous platforms into a single framework that’s highly functional, easy to work with, and extensible to boot. I think that Microsoft has hit a home run with Web API. Related Resources Where does ASP.NET Web API fit? Sample Source Code on GitHub Passing multiple POST parameters to Web API Controller Methods Mapping UrlEncoded POST Values in ASP.NET Web API Creating a JSONP Formatter for ASP.NET Web API Removing the XML Formatter from ASP.NET Web API Applications© Rick Strahl, West Wind Technologies, 2005-2012Posted in Web Api   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• The sign of a true manager is delegation (C# style)

  - by MarkPearl

  Today I thought I would write a bit about delegates in C#. Up till recently I have managed to side step any real understanding of what delegates do and why they are useful – I mean, I know roughly what they do and have used them a lot, but I have never really got down dirty with them and mucked about. Recently however with my renewed interest in Silverlight delegates came up again as a possible solution to a particular problem, and suddenly I found myself opening a bland little console application to just see exactly how far I could take delegates with my limited knowledge. So, let’s first look at the MSDN definition of delegates… A delegate declaration defines a reference type that can be used to encapsulate a method with a specific signature. A delegate instance encapsulates a static or an instance method. Delegates are roughly similar to function pointers in C++; however, delegates are type-safe and secure. Well, don’t you love MSDN for such a useful definition. I must give it credit though… later on it really explains it a bit better by saying “A delegate lets you pass a function as a parameter. The type safety of delegates requires the function you pass as a delegate to have the same signature as the delegate declaration.” A little more reading up on delegates mentions that delegates are similar to interfaces in that they enable the separation of specification and implementation. A delegate declares a single method, while an interface declares a group of methods. So enough reading - lets look at some code and see a basic example of a delegate… Let’s assume we have a console application with a simple delegate declared called AdjustValue like below… class Program { private delegate int AdjustValue(int val); static void Main(string[] args) { } } In a sense, all we have said is that we will be creating one or more methods that follow the same pattern as AdjustValue – i.e. they will take one input value of type int and return an integer. We could then expand our code to have various methods that match the structure of our delegate AdjustValue (remember the structure is int xxx (int xxx)) class Program { private delegate int AdjustValue(int val); private static int Dbl(int val) { return val * 2; } private static int AlwaysOne(int val) { return 1; } static void Main(string[] args) { } }  Above I have expanded my project to have two methods, one called Dbl and the other AlwaysOne. Dbl always returns double the input val and AlwaysOne always returns 1. I could now declare a variable and assign it to be one of those functions, like the following… class Program { private delegate int AdjustValue(int val); private static int Dbl(int val) { return val * 2; } private static int AlwaysOne(int val) { return 1; } static void Main(string[] args) { AdjustValue myDelegate; myDelegate = Dbl; Console.WriteLine(myDelegate(1).ToString()); Console.ReadLine(); } } In this instance I have declared an instance of the AdjustValue delegate called myDelegate; I have then told myDelegate to point to the method Dbl, and then called myDelegate(1). What would the result be? Yes, in this instance it would be exactly the same as me calling the following code… static void Main(string[] args) { Console.WriteLine(Dbl(1).ToString()); Console.ReadLine(); }   So why all the extra work for delegates when we could just do what we did above and call the method directly? Well… that separation of specification to implementation comes to mind. So, this all seems pretty simple. Let’s take a slightly more complicated variation to the console application. Assume that my project is the same as the one previously except that my main method is adjusted as follows… static void Main(string[] args) { AdjustValue myDelegate; myDelegate = Dbl; myDelegate = AlwaysOne; Console.WriteLine(myDelegate(1).ToString()); Console.ReadLine(); } What would happen in this scenario? Quite simply “1” would be written to the console, the reason being that myDelegate was last pointing to the AlwaysOne method before it was called. Make sense? In a way, the myDelegate is a variable method that can be swapped and changed when needed. Let’s make the code a little more confusing by using a delegate in the declaration of another delegate as shown below… class Program { private delegate int AdjustValue(InputValue val); private delegate int InputValue(); private static int Dbl(InputValue val) { return val()*2; } private static int GetInputVal() { Console.WriteLine("Enter a whole number : "); return Convert.ToInt32(Console.ReadLine()); } static void Main(string[] args) { AdjustValue myDelegate; myDelegate = Dbl; Console.WriteLine(myDelegate(GetInputVal).ToString()); Console.ReadLine(); } }   Now it gets really interesting because it looks like we have passed a method into a function in the main method by declaring… Console.WriteLine(myDelegate(GetInputVal).ToString()); So, what it the output? Well, try take a guess on what will happen – then copy the code and see if you got it right. Well that brings me to the end of this short explanation of Delegates. Hopefully it made sense!

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• Using reflection to change static final File.separatorChar for unit testing?

  - by Stefan Kendall

  Specifically, I'm trying to create a unit test for a method which requires uses File.separatorChar to build paths on windows and unix. The code must run on both platforms, and yet I get errors with JUnit when I attempt to change this static final field. Anyone have any idea what's going on? Field field = java.io.File.class.getDeclaredField( "separatorChar" ); field.setAccessible(true); field.setChar(java.io.File.class,'/'); When I do this, I get IllegalAccessException: Can not set static final char field java.io.File.separatorChar to java.lang.Character Thoughts?

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• how to link with static mySQL C library with Visual Studio 2008?

  - by Jean-Denis Muys

  Hi, My project is running fine, but its requirement for some DLLs means it cannot be simply dragged and dropped by the end user. The DLLs are not loaded when put side by side with my executable, because my executable is not an application, and its location is not in the few locations where Windows looks for DLL. I already asked a question about how to make their loading happen. None of the suggestions worked (see the question at http://stackoverflow.com/questions/2637499/how-can-a-win32-app-plugin-load-its-dll-in-its-own-directory) So I am now exploring another way: get rid of the DLLs altogether, and link with static versions of them. This is failing for the last of those DLLs. So I am at this point where all but one of the libraries are statically linked, and everything is fine. The last library is the standard C library for mySQL, aka Connector/C. The problem I have may or may not be related with that origin. Whenever I switched to the static library in the linker additional dependency, I get the following errors (log at the end): 1- about 40 duplicate symbols (e.g. _toupper) mutually between LIBCMT.lib and MSVCRT.lib. Interestingly, I can't control the inclusion of these two libraries: they are from Visual Studio and automatically included. So why are these symbol duplicate when I include mySQL's static lib, but not its DLL? Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\MSVCRT.lib: Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\OLDNAMES.lib: Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\msvcprt.lib: Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\LIBCMT.lib: LIBCMT.lib(setlocal.obj) : error LNK2005: _setlocale already defined in MSVCRT.lib(MSVCR90.dll) Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\MSVCRT.lib: MSVCRT.lib(MSVCR90.dll) : error LNK2005: _toupper already defined in LIBCMT.lib(toupper.obj) 2- two warnings that MSVCRT and LIBCMT conflicts with use of other libs, with a suggestion to use /NODEFAULTLIB:library:. I don't understand that suggestion: what am I supposed to do and how? LINK : warning LNK4098: defaultlib 'MSVCRT' conflicts with use of other libs; use /NODEFAULTLIB:library LINK : warning LNK4098: defaultlib 'LIBCMT' conflicts with use of other libs; use /NODEFAULTLIB:library 3- an external symbol is undefined: _main. So does that mean that the static mySQL lib (but not the DLL) references a _main symbol? For the sake of it, I tried to define an empty function named _main() in my code, with no difference. LIBCMT.lib(crt0.obj) : error LNK2001: unresolved external symbol _main As mentioned in my first question, my code is a port of a fully working Mac version of the code. Its a plugin for a host application that I don't control. The port currently works, albeit with installation issues due to that lone remaining DLL. As a Mac programmer I am rather disoriented with Visual Studio and Windows which I find confusing, poorly designed and documented, with error messages that are very difficult to grasp and act upon. So I will be very grateful for any help. Here is the full set of errors: 1 Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\MSVCRT.lib: 1 Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\OLDNAMES.lib: 1 Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\msvcprt.lib: 1 Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\LIBCMT.lib: 1LIBCMT.lib(setlocal.obj) : error LNK2005: _setlocale already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(tidtable.obj) : error LNK2005: __encode_pointer already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(tidtable.obj) : error LNK2005: __encoded_null already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(tidtable.obj) : error LNK2005: __decode_pointer already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(tolower.obj) : error LNK2005: _tolower already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(invarg.obj) : error LNK2005: __set_invalid_parameter_handler already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(invarg.obj) : error LNK2005: __invalid_parameter_noinfo already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(crt0dat.obj) : error LNK2005: __amsg_exit already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(crt0dat.obj) : error LNK2005: __initterm_e already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(crt0dat.obj) : error LNK2005: _exit already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(crtheap.obj) : error LNK2005: __malloc_crt already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(dosmap.obj) : error LNK2005: __errno already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(file.obj) : error LNK2005: __iob_func already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(mlock.obj) : error LNK2005: __unlock already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(mlock.obj) : error LNK2005: _lock already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(winxfltr.obj) : error LNK2005: __CppXcptFilter already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(crt0init.obj) : error LNK2005: ___xi_a already defined in MSVCRT.lib(cinitexe.obj) 1LIBCMT.lib(crt0init.obj) : error LNK2005: ___xi_z already defined in MSVCRT.lib(cinitexe.obj) 1LIBCMT.lib(crt0init.obj) : error LNK2005: ___xc_a already defined in MSVCRT.lib(cinitexe.obj) 1LIBCMT.lib(crt0init.obj) : error LNK2005: ___xc_z already defined in MSVCRT.lib(cinitexe.obj) 1LIBCMT.lib(hooks.obj) : error LNK2005: "void __cdecl terminate(void)" (?terminate@@YAXXZ) already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(winsig.obj) : error LNK2005: _signal already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(fflush.obj) : error LNK2005: _fflush already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(tzset.obj) : error LNK2005: __tzset already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(_ctype.obj) : error LNK2005: _isspace already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(_ctype.obj) : error LNK2005: _iscntrl already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(getenv.obj) : error LNK2005: _getenv already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(strnicmp.obj) : error LNK2005: __strnicmp already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(osfinfo.obj) : error LNK2005: __get_osfhandle already defined in MSVCRT.lib(MSVCR90.dll) 1LIBCMT.lib(osfinfo.obj) : error LNK2005: __open_osfhandle already defined in MSVCRT.lib(MSVCR90.dll) [...] 1 Searching C:\Program Files\Microsoft Visual Studio 9.0\VC\lib\MSVCRT.lib: 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _toupper already defined in LIBCMT.lib(toupper.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _isalpha already defined in LIBCMT.lib(_ctype.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _wcschr already defined in LIBCMT.lib(wcschr.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _isdigit already defined in LIBCMT.lib(_ctype.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _islower already defined in LIBCMT.lib(ctype.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: __doserrno already defined in LIBCMT.lib(dosmap.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _strftime already defined in LIBCMT.lib(strftime.obj) 1MSVCRT.lib(MSVCR90.dll) : error LNK2005: _isupper already defined in LIBCMT.lib(_ctype.obj) [...] 1Finished searching libraries 1 Creating library z:\PCdev\Test\RK_Demo_2004\plugins\Test.bundle\contents\windows\Test.lib and object z:\PCdev\Test\RK_Demo_2004\plugins\Test.bundle\contents\windows\Test.exp 1Searching libraries [...] 1Finished searching libraries 1LINK : warning LNK4098: defaultlib 'MSVCRT' conflicts with use of other libs; use /NODEFAULTLIB:library 1LINK : warning LNK4098: defaultlib 'LIBCMT' conflicts with use of other libs; use /NODEFAULTLIB:library 1LIBCMT.lib(crt0.obj) : error LNK2001: unresolved external symbol _main

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• C++ Project compiles as static lib, fails (linker error) as dynamic lib. why??

  - by Roey

  Hi All. I've a VS2008 native C++ project, that I wish to compile as a DLL. It only references one external library (log4cplus.lib), and uses its functions. (also uses log4cplus's .h files , naturally). When I try to compile my project as a static library, it succeeeds. When I try as DLL, it fails : 1>MessageWriter.obj : error LNK2019: unresolved external symbol "public: static class log4cplus::Logger __cdecl log4cplus::Logger::getInstance(class std::basic_string<wchar_t,struct std::char_traits<wchar_t>,class std::allocator<wchar_t> > const &)" (?getInstance@Logger@log4cplus@@SA?AV12@ABV?$basic_string@_WU?$char_traits@_W@std@@V?$allocator@_W@2@@std@@@Z) referenced in function "class log4cplus::Logger __cdecl Log(void)" (?Log@@YA?AVLogger@log4cplus@@XZ) There are 4 more errors just like this related to functions within log4cplus.lib. It seems like something really stupid.. please help me :) Thanks!

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• how to implement IOC without a global static service (non-service locator solution)?

  - by Michel

  Hi, we want to use Unity for IOC. All i've seen is the implementation that there is one global static service which holds a reference to the Unity container, which registers all interface/class combinations and every class asks that object: give me an implementation for Ithis or IThat. Frequently i see a response that this pattern is not good because it leads to a dependency from ALL classes to this service. But what i don't see often, is: what is the alternative way? Michel EDIT: found out that the global static service is called the service locator, added that to the title.

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• How do I access a JavaFX 1.3 static class member from Java?

  - by James

  I want to access a static JavaFX class member from Java using the Javafx reflection API. E.g. JavaFX code: var thing; class MyJavaFXClass { } Java code: private Object getThing() { FXClassType classType = FXContext.getInstance().findClass("mypackage.MyJavaFXClass"); // Get static member 'thing' from 'MyJavaFXClass' // <Insert Code Here> return thing; } What Java code do I need to access 'MyJavaFXClass.thing'? Note: I am using JavaFX 1.3 - I'm not sure if the reflection API is different here to earlier JavaFX versions.

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• How to define generic super type for static factory method?

  - by Esko

  If this has already been asked, please link and close this one. I'm currently prototyping a design for a simplified API of a certain another API that's a lot more complex (and potentially dangerous) to use. Considering the related somewhat complex object creation I decided to use static factory methods to simplify the API and I currently have the following which works as expected: public class Glue<T> { private List<Type<T>> types; private Glue() { types = new ArrayList<Type<T>>(); } private static class Type<T> { private T value; /* some other properties, omitted for simplicity */ public Type(T value) { this.value = value; } } public static <T> Glue<T> glueFactory(String name, T first, T second) { Glue<T> g = new Glue<T>(); Type<T> firstType = new Glue.Type<T>(first); Type<T> secondType = new Glue.Type<T>(second); g.types.add(firstType); g.types.add(secondType); /* omitted complex stuff */ return g; } } As said, this works as intended. When the API user (=another developer) types Glue<Horse> strongGlue = Glue.glueFactory("2HP", new Horse(), new Horse()); he gets exactly what he wanted. What I'm missing is that how do I enforce that Horse - or whatever is put into the factory method - always implements both Serializable and Comparable? Simply adding them to factory method's signature using <T extends Comparable<T> & Serializable> doesn't necessarily enforce this rule in all cases, only when this simplified API is used. That's why I'd like to add them to the class' definition and then modify the factory method accordingly. PS: No horses (and definitely no ponies!) were harmed in writing of this question.

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