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  • MySQL - Calculating fields on the fly vs storing calculated data

    - by Christian Varga
    Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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  • Different ways of accessing configuration parameters from a JAX-WS service

    - by ecerulm
    As far as I know I can access the web.xml <context-param>s by making my class implement ServletContextListener and use the ServletContext.getInitParam(String) to read them, but it´s cumbersome as only one instance of the class will receive the contextInitialized(ServletContextEvent sce) call, so I need to make the ServletContext an static member of the class. What other ways exist of setting conf params at deployment time and what are the recommended ones?

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  • due at midnight - program compiles but has logic error(s)

    - by Leslie Laraia
    not sure why this program isn't working. it compiles, but doesn't provide the expected output. the input file is basically just this: Smith 80000 Jones 100000 Scott 75000 Washington 110000 Duffy 125000 Jacobs 67000 Here is the program: import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner; /** * * @author Leslie */ public class Election { /** * @param args the command line arguments */ public static void main(String[] args) throws FileNotFoundException { // TODO code application logic here File inputFile = new File("C:\\Users\\Leslie\\Desktop\\votes.txt"); Scanner in = new Scanner(inputFile); int x = 0; String line = ""; Scanner lineScanner = new Scanner(line); line = in.nextLine(); while (in.hasNextLine()) { line = in.nextLine(); x++; } String[] senatorName = new String[x]; int[] votenumber = new int[x]; double[] votepercent = new double[x]; System.out.printf("%44s", "Election Results for State Senator"); System.out.println(); System.out.printf("%-22s", "Candidate"); //Prints the column headings to the screen System.out.printf("%22s", "Votes Received"); System.out.printf("%22s", "%of Total Votes"); int i; for(i=0; i<x; i++) { while(in.hasNextLine()) { line = in.nextLine(); String candidateName = lineScanner.next(); String candidate = candidateName.trim(); senatorName[i] = candidate; int votevalue = lineScanner.nextInt(); votenumber[i] = votevalue; } } votepercent = percentages(votenumber, x); for (i = 0; i < x; i++) { System.out.println(); System.out.printf("%-22s", senatorName[i]); System.out.printf("%22d", votenumber[i]); System.out.printf("%22.2f", votepercent[i]); System.out.println(); } } public static double [] percentages(int[] votenumber, int z) { double [] percentage = new double [z]; double total = 0; for (double element : votenumber) { total = total + element; } for(int i=0; i < votenumber.length; i++) { int y = votenumber[i]; percentage[i] = (y/total) * 100; } return percentage; } }

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  • Solving a cyclical dependency in Ninject (Compact Framework)

    - by Alex
    I'm trying to use Ninject for dependency injection in my MVP application. However, I have a problem because I have two types that depend on each other, thus creating a cyclic dependency. At first, I understand that it was a problem, because I had both types require each other in their constructors. Therefore, I moved one of the dependencies to a property injection instead, but I'm still getting the error message. What am I doing wrong? This is the presenter: public class LoginPresenter : Presenter<ILoginView>, ILoginPresenter { public LoginPresenter( ILoginView view ) : base( view ) { } } and this is the view: public partial class LoginForm : Form, ILoginView { [Inject] public ILoginPresenter Presenter { private get; set; } public LoginForm() { InitializeComponent(); } } And here's the code that causes the exception: static class Program { /// <summary> /// The main entry point for the application. /// </summary> [MTAThread] static void Main() { // Show the login form Views.LoginForm loginForm = Kernel.Get<Views.Interfaces.ILoginView>() as Views.LoginForm; Application.Run( loginForm ); } } The exception happens on the line with the Kernel.Get<>() call. Here it is: Error activating ILoginPresenter using binding from ILoginPresenter to LoginPresenter A cyclical dependency was detected between the constructors of two services. Activation path: 4) Injection of dependency ILoginPresenter into property Presenter of type LoginForm 3) Injection of dependency ILoginView into parameter view of constructor of type LoginPresenter 2) Injection of dependency ILoginPresenter into property Presenter of type LoginForm 1) Request for ILoginView Suggestions: 1) Ensure that you have not declared a dependency for ILoginPresenter on any implementations of the service. 2) Consider combining the services into a single one to remove the cycle. 3) Use property injection instead of constructor injection, and implement IInitializable if you need initialization logic to be run after property values have been injected. Why doesn't Ninject understand that since one is constructor injection and the other is property injection, this can work just fine? I even read somewhere looking for the solution to this problem that Ninject supposedly gets this right as long as the cyclic dependency isn't both in the constructors. Apparently not, though. Any help resolving this would be much appreciated.

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  • WPF ControlTemplate and Binding

    - by Vinjamuri
    In the below code, MousePressImage is a dependency property of class ButtonControl. The following Binding doesn't work.. Appreciate your help in solving this issue.. Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=MousePressImage}"/> -- I create the ButtonControl like this. <local:ButtonControl Height="48" Width="160" MouseOverImage="pack://application:,,,/Recipe_06_13;component/Resources/Over.bmp" MousePressImage="pack://application:,,,/Recipe_06_13;component/Resources/Press.bmp" DisableImage=" "> </local:ButtonControl>

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  • read length of string from stdin

    - by teoz
    I want to take a string from stdin but I don't want a static array of fixed size I know that scanf need something where save the stdin input, but I can't do something like this: char string[10] scanf("%s",string); becouse I need to know before how long will be the string in order to allocate the right memory space. Can you help me to resolve this problem?

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  • How to remove index from url in asp.net mvc?

    - by Pandiya Chendur
    I am doing a return RedirectToAction("Index", "Clients"); from my home controller.... It is fine but my url looks like http://localhost:1115/Clients/Index... How to remove index from url in asp.net mvc? Any suggestion.... My routes, public static void RegisterRoutes(RouteCollection routes) { routes.IgnoreRoute("{resource}.axd/{*pathInfo}"); routes.MapRoute( "Registrations", "{controller}/{action}/{id}", new { controller = "Registration", action = "Create", id = "" } ); }

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  • Set A Transparent Color

    - by Ngu Soon Hui
    I have a Color, and I have a method that should return a more "transparent" version of that color. I tried the following method: public static Color SetTransparency(int A, Color color) { return Color.FromArgb(A, Color.R, Color.G, Color.B); } but for some reason, no matter what the A is, the returned Color's transparency level just won't change. Any idea?

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  • Contravariant Delegates Value Types

    - by ChloeRadshaw
    Can anyone shed light on why contravariance does not work with C# value types? The below does not work private delegate Asset AssetDelegate(int m); internal string DoMe() { AssetDelegate aw = new AssetDelegate(DelegateMethod); aw(32); return "Class1"; } private static House DelegateMethod(object m) { return null; }

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  • Why is this simple Mobile Form not closed when using the player

    - by ajhvdb
    Hi, I created this simple sample Form with the close button. Everything is working as expected when NOT using the Interop.WMPLib.dll I've seen other applications using this without problems but why isn't the Form process closed when I just add the line: SoundPlayer myPlayer = new SoundPlayer(); and of course dispose it: if (myPlayer != null) { myPlayer.Dispose(); myPlayer = null; } The Form closes but the debugger VS2008 is still active. The Form project and the dll are still active. If you send me an email to [email protected], I can send you the zipped project. Below is the class for the dll: using System; using System.Collections.Generic; using System.Text; using System.Threading; using System.Runtime.InteropServices; using WMPLib; namespace WindowsMobile.Utilities { public delegate void SoundPlayerStateChanged(SoundPlayer sender, SoundPlayerState newState); public enum SoundPlayerState { Stopped, Playing, Paused, } public class SoundPlayer : IDisposable { [DllImport("coredll")] public extern static int waveOutSetVolume(int hwo, uint dwVolume); [DllImport("coredll")] public extern static int waveOutGetVolume(int hwo, out uint dwVolume); WindowsMediaPlayer myPlayer = new WindowsMediaPlayer(); public SoundPlayer() { myPlayer.uiMode = "invisible"; myPlayer.settings.volume = 100; } string mySoundLocation = string.Empty; public string SoundLocation { get { return mySoundLocation; } set { mySoundLocation = value; } } public void Pause() { myPlayer.controls.pause(); } public void PlayLooping() { Stop(); myPlayer.URL = mySoundLocation; myPlayer.settings.setMode("loop", true); } public int Volume { get { return myPlayer.settings.volume; } set { myPlayer.settings.volume = value; } } public void Play() { Stop(); myPlayer.URL = mySoundLocation; myPlayer.controls.play(); } public void Stop() { myPlayer.controls.stop(); myPlayer.close(); } #region IDisposable Members public void Dispose() { try { Stop(); } catch (Exception) { } // need this otherwise the process won't exit?! try { int ret = Marshal.FinalReleaseComObject(myPlayer); } catch (Exception) { } myPlayer = null; GC.Collect(); } #endregion } }

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  • Your creative PHP Obfuscation - Dynamic Variables

    - by Email
    Hi No thread about use or unuse of obfuscusion please ^^ Just share creative approaches how to obfuscate in php the really smart way plz. plain md5 and base64_decode is too static .. what you think regarding hash, salt what about dynamic Variables (even for the same $var). Thx for any creative input

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  • help me understand the method Validator.TryValidateObject()

    - by Benny
    this is the method definition: public static bool TryValidateObject( Object instance, ValidationContext validationContext, ICollection<ValidationResult> validationResults, bool validateAllProperties ) what i am confused is the validateAllProperties parameter, I understand when it is true-validate all properties. What about when it is false, not validate all properties, but which property will be validated?

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  • What makes a Winform position initially stale?

    - by msorens
    The code below demonstrates a very simple problem; I am hoping that I am just missing a setting that someone might be able to reveal. Goal (1) Launch main winform (MainForm). (2) Press button to display secondary winform (ShadowForm) that is semi-transparent and should exactly overlay MainForm. What Actually Happens Scenario 1: Launch main winform then press button: ShadowForm displays with correct size but incorrect location, lower and to the right (as if it was cascaded). Press button to close ShadowForm again. Press button once more to reopen ShadowForm and now it is in the correct position, covering MainForm. Scenario 2: Launch main winform, move it around, then press button: ShadowForm displays with correct size but incorrect location (where the MainForm was before moving it). Press button to close; press again to reopen and now ShadowForm is in the correct position. using System; using System.Windows.Forms; namespace LocationTest { static class Program { static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new MainForm()); } } public class MainForm : Form { ShadowForm shadowForm = new ShadowForm(); Button button1 = new Button(); System.ComponentModel.IContainer components = null; public MainForm() { this.SuspendLayout(); this.button1.Location = new System.Drawing.Point(102, 44); this.button1.Size = new System.Drawing.Size(75, 23); this.button1.Text = "button1"; this.button1.Click += new System.EventHandler(this.button1_Click); this.ClientSize = new System.Drawing.Size(292, 266); this.Controls.Add(this.button1); this.ResumeLayout(false); } private void button1_Click(object sender, EventArgs e) { if (shadowForm.Visible) { shadowForm.Hide(); } else { shadowForm.Size = Size; // this always works shadowForm.Location = Location; // this fails first time, but works second time! shadowForm.Show(); } } protected override void Dispose(bool disposing) { if (disposing && (components != null)) { components.Dispose(); } base.Dispose(disposing); } } public class ShadowForm : Form { private System.ComponentModel.IContainer components = null; public ShadowForm() { this.SuspendLayout(); this.BackColor = System.Drawing.Color.Black; this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None; this.Opacity = 0.5; this.Click += new System.EventHandler(this.ShadowForm_Click); this.ResumeLayout(false); } private void ShadowForm_Click(object sender, EventArgs e) { Hide(); } protected override void Dispose(bool disposing) { if (disposing && (components != null)) { components.Dispose(); } base.Dispose(disposing); } } }

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  • Asp.net Mvc - Kigg: Maintain User object in HttpContext.Items between requests.

    - by Pickels
    Hallo, first I want to say that I hope this doesn't look like I am lazy but I have some trouble understanding a piece of code from the following project. http://kigg.codeplex.com/ I was going through the source code and I noticed something that would be usefull for my own little project I am making. In their BaseController they have the following code: private static readonly Type CurrentUserKey = typeof(IUser); public IUser CurrentUser { get { if (!string.IsNullOrEmpty(CurrentUserName)) { IUser user = HttpContext.Items[CurrentUserKey] as IUser; if (user == null) { user = AccountRepository.FindByClaim(CurrentUserName); if (user != null) { HttpContext.Items[CurrentUserKey] = user; } } return user; } return null; } } This isn't an exact copy of the code I adjusted it a little to my needs. This part of the code I still understand. They store their IUser in HttpContext.Items. I guess they do it so that they don't have to call the database eachtime they need the User object. The part that I don't understand is how they maintain this object in between requests. If I understand correctly the HttpContext.Items is a per request cache storage. So after some more digging I found the following code. internal static IDictionary<UnityPerWebRequestLifetimeManager, object> GetInstances(HttpContextBase httpContext) { IDictionary<UnityPerWebRequestLifetimeManager, object> instances; if (httpContext.Items.Contains(Key)) { instances = (IDictionary<UnityPerWebRequestLifetimeManager, object>) httpContext.Items[Key]; } else { lock (httpContext.Items) { if (httpContext.Items.Contains(Key)) { instances = (IDictionary<UnityPerWebRequestLifetimeManager, object>) httpContext.Items[Key]; } else { instances = new Dictionary<UnityPerWebRequestLifetimeManager, object>(); httpContext.Items.Add(Key, instances); } } } return instances; } This is the part where some magic happens that I don't understand. I think they use Unity to do some dependency injection on each request? In my project I am using Ninject and I am wondering how I can get the same result. I guess InRequestScope in Ninject is the same as UnityPerWebRequestLifetimeManager? I am also wondering which class/method they are binding to which interface? Since the HttpContext.Items get destroyed each request how do they prevent losing their user object? Anyway it's kinda a long question so I am gradefull for any push in the right direction. Kind regards, Pickels

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  • Write PEM encoded certificate in file - java

    - by user1349407
    Good day. I recently create X.509 certificate by using bouncy castle API. I need to save the certificate result rather than display the result. I tried to use FileOutputStream, but it does not work. regards the result is like follows -----BEGIN CERTIFICATE----- MIICeTCCAeKgAwIBAgIGATs8OWsXMA0GCSqGSIb3DQEBCwUAMBsxGTAXBgNVBAMT... -----END CERTIFICATE----- The code is belows import java.io.FileOutputStream; //example of a basic CA public class PKCS10CertCreateExample { public static X509Certificate[] buildChain() throws Exception { //create the certification request KeyPair pair = chapter7.Utils.generateRSAKeyPair(); PKCS10CertificationRequest request = PKCS10ExtensionExample.generateRequest(pair); //create a root certificate KeyPair rootPair=chapter7.Utils.generateRSAKeyPair(); X509Certificate rootCert = X509V1CreateExample.generateV1Certificate (rootPair); //validate the certification request if(!request.verify("BC")) { System.out.println("request failed to verify!"); System.exit(1); } //create the certificate using the information in the request X509V3CertificateGenerator certGen = new X509V3CertificateGenerator(); certGen.setSerialNumber(BigInteger.valueOf(System.currentTimeMillis())); certGen.setIssuerDN(rootCert.getSubjectX500Principal()); certGen.setNotBefore(new Date(System.currentTimeMillis())); certGen.setNotAfter(new Date(System.currentTimeMillis()+50000)); certGen.setSubjectDN(request.getCertificationRequestInfo().getSubject()); certGen.setPublicKey(request.getPublicKey("BC")); certGen.setSignatureAlgorithm("SHA256WithRSAEncryption"); certGen.addExtension(X509Extensions.AuthorityKeyIdentifier, false, new AuthorityKeyIdentifierStructure(rootCert)); certGen.addExtension(X509Extensions.SubjectKeyIdentifier, false, new SubjectKeyIdentifierStructure(request.getPublicKey("BC"))); certGen.addExtension(X509Extensions.BasicConstraints, true, new BasicConstraints(false)); //certGen.addExtension(X509Extensions.KeyUsage, true, new BasicConstraints(false)); certGen.addExtension(X509Extensions.KeyUsage, true, new KeyUsage(KeyUsage.digitalSignature | KeyUsage.keyEncipherment)); certGen.addExtension(X509Extensions.ExtendedKeyUsage, true, new ExtendedKeyUsage(KeyPurposeId.id_kp_serverAuth)); //extract the extension request attribute ASN1Set attributes = request.getCertificationRequestInfo().getAttributes(); for(int i=0;i!=attributes.size();i++) { Attribute attr = Attribute.getInstance(attributes.getObjectAt(i)); //process extension request if(attr.getAttrType().equals(PKCSObjectIdentifiers.pkcs_9_at_extensionRequest)) { X509Extensions extensions = X509Extensions.getInstance(attr.getAttrValues().getObjectAt(0)); Enumeration<?> e = extensions.oids(); while(e.hasMoreElements()) { DERObjectIdentifier oid = (DERObjectIdentifier)e.nextElement(); X509Extension ext = extensions.getExtension(oid); certGen.addExtension(oid, ext.isCritical(), ext.getValue().getOctets()); } } } X509Certificate issuedCert = certGen.generateX509Certificate(rootPair.getPrivate()); return new X509Certificate[]{issuedCert, rootCert}; } public static void main(String[] args) throws Exception { X509Certificate[] chain = buildChain(); PEMWriter pemWrt = new PEMWriter(new OutputStreamWriter(System.out)); pemWrt.writeObject(chain[0]); //pemWrt.writeObject(chain[1]); pemWrt.close(); //write it out //FileOutputStream fOut = new FileOutputStream("pkcs10req.req"); //fOut.write(chain[0].toString()); //fOut.write() //System.out.println(chain[0].toString()); //fOut.close(); } }

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  • Has the `message-passing/shared-state' dilemma (concurrency & distribution) taken form of a `Holywar

    - by Bubba88
    I'm not too well-informed about the state of the discussion about which model is better, so I would like to ask a pretty straight question: Does it look like two opposing views having really heatened dispute? E.g. like prototype/class based OOP or dynamic vs. static typing (though these are really not much fitting examples, I just do not know how to express my question more clearly)

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  • Warning: newtype `CInt' is used in an FFI declaration,

    - by vivian
    When building gtk2hs-buildtools with ghc 7.4.2, I get the following warning: c2hs/toplevel/C2HSConfig.hs:110:1: Warning: newtype `CInt' is used in an FFI declaration, but its constructor is not in scope. This will become an error in GHC 7.6.1. When checking declaration: foreign import ccall safe "static bitfield_direction" bitfield_direction :: CInt I get similar warnings with FFI calls, even though I have import Foreign.C.Types(CInt). What is the correct way of getting rid of this warning?

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  • iphone :- i have one webservice in that Authentication require

    - by Heart PAL
    hello, i have one webservice given by my client ... problem is this webservise require Authentication...without username and password no one get data from this url...so how can i do authentication this webservice . this is same like u r gling to login to facebook or twitter then first we enter username and password for authenticate . how can i do this same. i have username and password for this webservise can i pass this static data in code ?

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  • 2 roles, admin and user. Is using anything other than basic http auth overkill?

    - by juststarting
    I'm building my first website with rails,it consists of a blog, a few static pages and a photo gallery. The admin section has namespaced controllers. I also want to create a mailing list, collecting contact info, (maybe a spree store in the future too.) Should I just use basic http authentication and check if the user is admin? Or is a plugin like authlogic better, then define user roles even though there would only be two; admin and user?

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  • C++ keeping a list of objects and calling a contructor through another function

    - by Nona Urbiz
    why isnt my object being created? When I do it like so, I am told error C2065: 'AllReferrals' : undeclared identifier as well as error C2228: left of '.push_back' must have class/struct/union. If I put the list initialization before the class I get error C2065: 'AllReferrals' : undeclared identifier. Thanks! #include <iostream> #include <fstream> #include <regex> #include <string> #include <list> #include <map> using namespace std; using namespace tr1; class Referral { public: string url; map<string, int> keywords; static bool submit(string url, string keyword, int occurrences) { //if(lots of things i'll later add){ Referral(url, keyword, occurrences); return true; //} //else // return false; } private: list<string> urls; Referral(string url, string keyword, int occurrences) { url = url; keywords[keyword] = occurrences; AllReferrals.push_back(this); } }; static list<Referral> AllReferrals; int main() { Referral::submit("url", "keyword", 1); cout << AllReferrals.size(); cout << "\n why does that ^^ say 0 (help me make it say one)?"; cout << "\n and how can i AllReferrals.push_back(this) from my constructor?"; cout << " When I do it like so, I am told error C2065: 'AllReferrals' : undeclared identifier"; cout << " as well as error C2228: left of '.push_back' must have class/struct/union."; cout << " If I put the list initialization before the class I get error C2065: 'AllReferrals' : undeclared identifier."; cout << "\n\n\t Thanks!"; getchar(); }

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  • JSP functions - How to declare long as parameter in TLD

    - by Spines
    I'm getting an error WARNING: Method "pl" for function "pl" not found, I think its because I'm not declaring the parameters right. <function-signature>java.lang.String pl(java.lang.Long, java.lang.String)</function-signature> is what I have in the TLD. and public static String pl(long num, String str) is what I have in the .java file.

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