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• Extending Throwable in Java

  - by polygenelubricants

  Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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• ELMAH - Using custom error pages to collecting user feedback

  - by vdh_ant

  Hey guys I'm looking at using ELMAH for the first time but have a requirement that needs to be met that I'm not sure how to go about achieving... Basically, I am going to configure ELMAH to work under asp.net MVC and get it to log errors to the database when they occur. On top of this I be using customErrors to direct the user to a friendly message page when an error occurs. Fairly standard stuff... The requirement is that on this custom error page I have a form which enables to user to provide extra information if they wish. Now the problem arises due to the fact that at this point the error is already logged and I need to associate the loged error with the users feedback. Normally, if I was using my own custom implementation, after I log the error I would pass through the ID of the error to the custom error page so that an association can be made. But because of the way that ELMAH works, I don't think the same is quite possible. Hence I was wondering how people thought that one might go about doing this.... Cheers UPDATE: My solution to the problem is as follows: public class UserCurrentConextUsingWebContext : IUserCurrentConext { private const string _StoredExceptionName = "System.StoredException."; private const string _StoredExceptionIdName = "System.StoredExceptionId."; public virtual string UniqueAddress { get { return HttpContext.Current.Request.UserHostAddress; } } public Exception StoredException { get { return HttpContext.Current.Application[_StoredExceptionName + this.UniqueAddress] as Exception; } set { HttpContext.Current.Application[_StoredExceptionName + this.UniqueAddress] = value; } } public string StoredExceptionId { get { return HttpContext.Current.Application[_StoredExceptionIdName + this.UniqueAddress] as string; } set { HttpContext.Current.Application[_StoredExceptionIdName + this.UniqueAddress] = value; } } } Then when the error occurs, I have something like this in my Global.asax: public void ErrorLog_Logged(object sender, ErrorLoggedEventArgs args) { var item = new UserCurrentConextUsingWebContext(); item.StoredException = args.Entry.Error.Exception; item.StoredExceptionId = args.Entry.Id; } Then where ever you are later you can pull out the details by var item = new UserCurrentConextUsingWebContext(); var error = item.StoredException; var errorId = item.StoredExceptionId; item.StoredException = null; item.StoredExceptionId = null; Note this isn't 100% perfect as its possible for the same IP to have multiple requests to have errors at the same time. But the likely hood of that happening is remote. And this solution is independent of the session, which in our case is important, also some errors can cause sessions to be terminated, etc. Hence why this approach has worked nicely for us.

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• Writing catch block with cleanup operations in Java ...

  - by kedarmhaswade

  I was not able to find any advise on catch blocks in Java that involve some cleanup operations which themselves could throw exceptions. The classic example is that of stream.close() which we usually call in the finally clause and if that throws an exception, we either ignore it by calling it in a try-catch block or declare it to be rethrown. But in general, how do I handle cases like: public void doIt() throws ApiException { //ApiException is my "higher level" exception try { doLower(); } catch(Exception le) { doCleanup(); //this throws exception too which I can't communicate to caller throw new ApiException(le); } } I could do: catch(Exception le) { try { doCleanup(); } catch(Exception e) { //ignore? //log? } throw new ApiException(le); //I must throw le } But that means I will have to do some log analysis to understand why cleanup failed. If I did: catch(Exception le) { try { doCleanup(); } catch(Exception e) { throw new ApiException(e); } It results in losing the le that got me here in the catch block in the fist place. What are some of the idioms people use here? Declare the lower level exceptions in throws clause? Ignore the exceptions during cleanup operation?

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• Rails - handling global site settings

  - by egarcia

  I'm developing a new rails application which is supposed to be installed several times in order to implement several sites. There are some things, like the "Site Title" or the "Default Number of Items per Page" that clearly belong to a "global settings" table / config file. I've made a list of the things I think I'll need: ActiveRecord model that is capable of: Storing different kinds of data. I suppose this would be accomplished encoding the values on a string on the db, probably with a "type" field. Indexing settings by name Validations based on a "type" attribute (i.e. don't accept invalid dates on "date" settings) Validations based on a allows_nil property. A controller that allows me to change settings via views. I'm pretty sure I could implement this myself, but I'm not willing to reinvent the wheel. I've done some searching, but I could only find rails-settings, which doesn't really serve me: I need a proper model & controller so I can use declarative-authorization, and it does not provide any controller or view facilities. Is there a gem or plugin out there that implements what I want, or any library I should look at? Thanks a lot.

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• Why should I not wrap every block in "try"-"catch"?

  - by Konrad

  I have always been of the belief that if a method can throw an exception then it is reckless not to protect this call with a meaningful try block. I just posted 'You should ALWAYS wrap calls that can throw in try, catch blocks.' to this question and was told that it was 'remarkably bad advice' - I'd like to understand why. Thanks!

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• Handling over-long UTF-8 sequences

  - by Grant McLean

  I've just been reworking my Encoding::FixLatin Perl module to handle over-long utf8 byte sequences and convert them to the shortest normal form. My question is quite simply "is this a bad idea"? A number of sources (including this RFC) suggest that any over-long utf8 should be treated as an error and rejected. They caution against "naive implementations" and leave me with the impression that these things are inherently unsafe. Since the whole purpose of my module is to clean up messy data files with mixed encodings and convert them to nice clean utf8, this seems like just one more thing I can clean up so the application layer doesn't have to deal with it. My code does not concern itself with any semantic meaning the resulting characters might have, it simply converts them into a normalised form. Am I missing something. Is there a hidden danger I haven't considered?

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• Cross platform unicode path handling

  - by Matt Joiner

  I'm using boost::filesystem for cross-platform path manipulation, but this breaks down when calls need to be made down into interfaces I don't control that won't accept UTF-8. For example when using the Windows API, I need to convert to UTF-16, and then call the wide-string version of whatever function I was about to call, and then convert any output back to UTF-8. While the wpath, and other w* forms of many of the boost::filesystem functions help keep sanity, are there any suggestions for how best to handle this conversion to wide-string forms where needed, while maintaining consistency in my own code?

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• dynamically created controls and responding to control events

  - by Dirk

  I'm working on an ASP.NET project in which the vast majority of the forms are generated dynamically at run time (form definitions are stored in a DB for customizability). Therefore, I have to dynamically create and add my controls to the Page every time OnLoad fires, regardless of IsPostBack. This has been working just fine and .NET takes care of managing ViewState for these controls. protected override void OnLoad(EventArgs e) { base.OnLoad(e); RenderDynamicControls() } private void RenderDynamicControls(){ //1. call service layer to retrieve form definition //2. create and add controls to page container } I have a new requirement in which if a user clicks on a given button (this button is created at design time) the page should be re-rendered in a slightly different way. So in addition to the code that executes in OnLoad (i.e. RenderDynamicControls()), I have this code: protected void MyButton_Click(object sender, EventArgs e) { RenderDynamicControlsALittleDifferently() } private void RenderDynamicControlsALittleDifferently() (){ //1. clear all controls from the page container added in RenderDynamicControls() //2. call service layer to retrieve form definition //3. create and add controls to page container } My question is, is this really the only way to accomplish what I'm after? It seems beyond hacky to effectively render the form twice simply to respond to a button click. I gather from my research that this is simply how the page-lifecycle works in ASP.NET: Namely, that OnLoad must fire on every Postback before child events are invoked. Still, it's worthwhile to check with the SO community before having to drink the kool-aid. On a related note, once I get this feature completed, I'm planning on throwing an UpdatePanel on the page to perform the page updates via Ajax. Any code/advice that make that transition easier would be much appreciated. Thanks

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• ASP.NET MVC: Returning a view with querystring in tact

  - by ajbeaven

  I'm creating a messaging web app in ASP.NET and are having some problems when displaying an error message to the user if they go to send a message and there is something wrong. A user can look through profiles of people and then click, 'send a message'. The following action is called (url is /message/create?to=username) and shows them a page where they can enter their message and send it: public ActionResult Create(string to) { ViewData["recipientUsername"] = to; return View(); } On the page that is displayed, the username is entered in to a hidden input field. When the user clicks 'send': [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create(string message, string to) { try { //do message stuff that errors out } catch { ModelState.AddModelErrors(message.GetRuleViolations()); //adding errors to modelstate } return View(); } So now the error message is displayed to the user fine, however the url is changed in that it no longer has the querystring (/message/create). Again, this would be fine except that when the user clicks the refresh button, the page errors out as the Create action no longer has the 'to' parameter. So I'm guessing that I need to maintain my querystring somehow. Is there any way to do this or do I need to use a different method altogether?

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• Handling Character Encoding in URI on Tomcat

  - by ZZ Coder

  On the web site I am trying to help with, user can type in an URL in the browser, like following Chinese characters, http://localhost:8080?a=?? On server, we get GET /a=%E6%B5%8B%E8%AF%95 HTTP/1.1 As you can see, it's UTF-8 encoded, then URL encoded. We can handle this correctly by setting encoding to UTF-8 in Tomcat. However, sometimes we get Latin1 encoding on certain browsers, http://localhost:8080?a=ß turns into GET /a=%DF HTTP/1.1 Is there anyway to handle this correctly in Tomcat? Looks like the server has to do some intelligent guessing. We don't expect to handle the Latin1 correctly 100% but anything is better than what we are doing now by assuming everything is UTF-8. The server is Tomcat 5.5. The supported browsers are IE 6+, Firefox 2+ and Safari on iPhone.

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• need to get the context value in top of page, where the context value will be set only at the bottom

  - by Mahadevan Alagar

  <script runat="server"> protected void Page_Load(object sender, EventArgs e) { Response.Write("Page Load:"); } public string setContext(string sName, string sVal) { HttpContext.Current.Items[sName] = sVal; return sVal; } public string getContext(string sName) { string sVal = "default"; if (HttpContext.Current.Items[sName] != null) sVal = HttpContext.Current.Items[sName].ToString(); else sVal = "empty"; return sVal; } </script> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Get Context in TOP ???</title> </head> <body> <div> <div id="divDest" name="divDest"> Top Content: Get1 :<%= getContext("topcontent") %> // returns "empty", BUT I Need "value to set" </div> <br /> Set1 : <%= setContext("topcontent", "value to set")%> <br /> // set the value <br /> Get2 : <%= getContext("topcontent") %><br /> // returns "value to set" <br /> <script language="javascript"> var elval = getElementVal("divTest"); document.getElementById("divDest").innerHTML = elval; //alert(elval); function getElementVal(elemid) { var elemval = document.getElementById(elemid); return elemval.innerHTML; } </script> </body> </html> I need to get the context value in top of page, where the context value will be set at the bottom of the page. Get context value == "empty", BUT need "something" Set context value to "something" Get context value == "something" I may use JS/AJAX, where the page source the value won't be present. BUT I need the TEXT in the View Source of the page too. Is there a way to wait for the context to set and then get, I have tried with User Control, prerender and render methods too. But I can't able to get it right. Any idea?

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• "Unable to open file", when the program tries to open file in /proc

  - by tristartom

  Hi, I try to read file /proc/'pid'/status, using c program. The code is as follows, and even I use sudo to run it, the prompt still keeps throwing "Unable to open file". Please let me know if you have any ideas on how to fix this. thanks Richard ... int main (int argc, char* argv[]) { string line; char* fileLoc; if(argc != 2) { cout << "a.out file_path" << endl; fileLoc = "/proc/net/dev"; } else { sprintf(fileLoc, "/proc/%d/status", atoi(argv[1])); } cout<< fileLoc << endl; ifstream myfile (fileLoc); if (myfile.is_open()) { while (! myfile.eof() ) { getline (myfile,line); cout << line << endl; } myfile.close(); } else cout << "Unable to open file"; return 0; }

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• Ruby: Continue a loop after catching an exception

  - by Santa

  Basically, I want to do something like this (in Python, or similar imperative languages): for i in xrange(1, 5): try: do_something_that_might_raise_exceptions(i) except: continue # continue the loop at i = i + 1 How do I do this in Ruby? I know there are the redo and retry keywords, but they seem to re-execute the "try" block, instead of continuing the loop: for i in 1..5 begin do_something_that_might_raise_exceptions(i) rescue retry # do_something_* again, with same i end end

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• Squid handling of concurrent cache misses

  - by Oliver H-H

  We're using a Squid cache to off-load traffic from our web servers, ie. it's setup as a reverse-proxy responding to inbound requests before they hit our web servers. When we get blitzed with concurrent requests for the same request that's not in the cache, Squid proxies all the requests through to our web ("origin") servers. For us, this behavior isn't ideal: our origin servers gets bogged down trying to fulfill N identical requests concurrently. Instead, we'd like the first request to proxy through to the origin server, the rest of the requests to queue at the Squid layer, and then all be fulfilled by Squid when the origin server has responded to that first request. Does anyone know how to configure Squid to do this? We've read through the documentation multiple times and thoroughly web-searched the topic, but can't figure out how to do it. We use Akamai too and, interestingly, this is its default behavior. (However, Akamai has so many nodes that we still see lots of concurrent requests in certain traffic spike scenarios, even with Akamai's super-node feature enabled.) This behavior is clearly configurable for some other caches, eg. the Ehcache documentation offers the option "Concurrent Cache Misses: A cache miss will cause the filter chain, upstream of the caching filter to be processed. To avoid threads requesting the same key to do useless duplicate work, these threads block behind the first thread." Some folks call this behavior a "blocking cache," since the subsequent concurrent requests block behind the first request until it's fulfilled or timed-out. Thx for looking over my noob question! Oliver

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• Preventing a button from responding to 'Enter' in ASP.net

  - by kd7iwp

  I have a master template that all the pages on my site use. In the template there is an empty panel. In the code-behind for the page an imagebutton is created in the panel dynamically in my Page_Load section (makes a call to the DB to determine which button should appear via my controller). On some pages that use this template and have forms on them, pressing the Enter key fires the click event on this imagebutton rather than the submit button in the form. Is there a simple way to prevent the imagebutton click event from firing unless it's clicked by the mouse? I'm thinking a javascript method is a hack, especially since the button doesn't even exist in the master template until the button is dynamically created on Page_Load (this is ugly since I can't simply do <% =btnName.ClientId %> to refer to the button's name in my aspx page). I tried setting a super-high tabindex for the image button and that did nothing. Also set the button to be the DefaultButton in its panel on the master template but that did not work either.

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• ASP.NET: disabling authentication for a single aspx page (custom error page)?

  - by Richard Collette

  I am using a custom error page: <customErrors redirectMode="ResponseRedirect" mode="On" defaultRedirect="Error2.aspx"/> I want to disable authentication for the custom error page because the error being raised is related to an authentication module and I don't want to get into an infinite loop and I want to display a clean error page to the user. I have been trying the following configuration to do that. <location path="Error2.aspx"> <system.web> <authentication mode="None"/> <authorization> <allow users="?"/> <allow users="*"/> </authorization> </system.web> </location> I am getting a System.Configuration.ConfigurationErrorsException for the line that sets the authentication mode. It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS. I have verified that there are no other web.config files in subdirectories under the application's folder. The applications folder is configured as an application in IIS and the error page is at the application's root. File permissions set for the error page in IIS include anonymous and windows authentication (I have tried just anonymous as well).

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• Is checking for exceptions in code or using try-catch a better practice in Java?

  - by badpanda

  I had someone mention to me that catching all exceptions is not necessarily good practice (for example, NullPointerException). I am looking for an explanation of when this is a good thing, when it is not, and why it is as such :D Thanks!! badPanda

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• Handling Status Bar notification

  - by MAkS

  in my app a background service starts and from that service i want to set Status bar notification, that the service has Started following is the code : Context context = getApplicationContext(); String ns = Context.NOTIFICATION_SERVICE; int icon = R.drawable.icon; CharSequence tickerText = "Hello"; long when = System.currentTimeMillis(); Notification notification = new Notification(icon, tickerText, when); CharSequence contentTitle = "My notification"; CharSequence contentText = "Hello World!"; Intent notificationIntent = new Intent(MyService.this, MyClass.class); notificationIntent.setFlags( Intent.FLAG_ACTIVITY_NEW_TASK); PendingIntent contentIntent = PendingIntent.getActivity(this,0,notificationIntent,0); notification.setLatestEventInfo(context, contentTitle, contentText, contentIntent); NotificationManager mNotificationManager = (NotificationManager) getSystemService(ns); mNotificationManager.notify(1, notification); Notification is displayed in Status bar But whin i click on that MyClass.class is not fired.And in log cat it shows "Input Manager Service Window already focused ignoring focuson ...." so plz provide solution. thanks in advance

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• How to get ANTLR 3.2 to exit upon first error?

  - by Dan Becker

  In section 10.4, The Definitive ANTLR reference tells you to override mismatch() & recoverFromMismatchedSet() if you want to exit upon the first parsing error. But, at least in ANTLR 3.2, it appears that there is no mismatch() method, and the recoverFromMismatchedSet() documentation says that it is "Not Currently Used". So it appears things have changed since the book was published. What am I supposed to do instead to exit upon the first parsing error in ANTLR 3.2?

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• Trap error or 'Resume Next'

  - by Craig Johnston

  I realise this is an older programming environment, but I have to clean up some VB6 code and I am finding that most of it uses: Resume Next What is the general consensus about the use of Resume Next? Surely, if there is an error, you would want the app to stop what it was doing, rollback any data changes, and inform the user of the error, rather than just resuming. When is it good idea to use Resume?

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• Java: how to access assignments in try-catch -loop?

  - by HH

  $ javac TestInit2.java TestInit2.java:13: variable unknown might not have been initialized System.out.println(unknown); ^ 1 error Code import java.util.*; import java.io.*; public class TestInit2 { public static void main(String[] args){ String unknown; try{ unknown="cannot see me, why?"; }catch(Exception e){ e.printStackTrace(); } System.out.println(unknown); } }

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• Raising C# events with an extension method - is it bad?

  - by Kyralessa

  We're all familiar with the horror that is C# event declaration. To ensure thread-safety, the standard is to write something like this: public event EventHandler SomethingHappened; protected virtual void OnSomethingHappened(EventArgs e) { var handler = SomethingHappened; if (handler != null) handler(this, e); } Recently in some other question on this board (which I can't find now), someone pointed out that extension methods could be used nicely in this scenario. Here's one way to do it: static public class EventExtensions { static public void RaiseEvent(this EventHandler @event, object sender, EventArgs e) { var handler = @event; if (handler != null) handler(sender, e); } static public void RaiseEvent<T>(this EventHandler<T> @event, object sender, T e) where T : EventArgs { var handler = @event; if (handler != null) handler(sender, e); } } With these extension methods in place, all you need to declare and raise an event is something like this: public event EventHandler SomethingHappened; void SomeMethod() { this.SomethingHappened.RaiseEvent(this, EventArgs.Empty); } My question: Is this a good idea? Are we missing anything by not having the standard On method? (One thing I notice is that it doesn't work with events that have explicit add/remove code.)

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• How do I add and remove an event listener using a function with parameters?

  - by Bungle

  Sorry if this is a common question, but I couldn't find any answers that seemed pertinent through searching. If I attach an event listener like this: window.addEventListener('scroll', function() { check_pos(box); }, false); it doesn't seem to work to try to remove it later, like this: window.removeEventListener('scroll', function() { check_pos(box); }, false); I assume this is because the addEventListener and removeEventListener methods want a reference to the same function, while I've provided them with anonymous functions, which, while identical in code, are not literally the same. How can I change my code to get the call to removeEventListener to work? The "box" argument refers to the name of an <iframe> that I'm tracking on the screen; that is, I want to be able to subscribe to the scroll event once for each <iframe> that I have (the quantity varies), and once the check_pos() function measures a certain position, it will call another function and also remove the event listener to free up system resources. My hunch is that the solution will involve a closure and/or naming the anonymous function, but I'm not sure exactly what that looks like, and would appreciate a concrete example. Hope that makes sense. Thanks for any help!

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• DataPager EventArgs

  - by philbrowndotcom

  I'm using a DataPager control in my silverlight application. I have different pagers for different DataGrids and want to use the same event handler for the PageIndexChanged event for all of them. The delegate must take an EventArgs object as an argument. Can I use this object to "get back" to the control from which the event was fired?

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• DST change handling in a daemon process (*NIX)

  - by CodeMedic

  In a *NIX environment, if I have a 24x7 running application, how do I handle DST changes? I am looking for a solution for my app written in C/C++.

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