Loading EAR or WAR using a Custom Classloader

Hi, everybody.
First of all I'm aware of http://download.oracle.com/docs/cd/E12840_01/wls/docs103/programming/classloading.html
Is is possible to "insert" a custom classloader in this hierarchy? I need a custom classloader to load special resources for my webapp. This custom classloader can be added right after the system classloader, acting as the parent classloader of my app (ear or war) classloader. Is it doable? How?
Thanks in advance.
Best regards,
Daniel.

My workaround won't work. The app classloader is accessible but it isn't an URLClassLoader, so i am unable to change its classpath.
<16/05/2011 18h01min11s BRT> <Notice> <WebLogicServer> <BEA-000365> <Server state changed to STANDBY>
<16/05/2011 18h01min11s BRT> <Notice> <WebLogicServer> <BEA-000365> <Server state changed to STARTING>
preStart
thread cl = weblogic.utils.classloaders.GenericClassLoader@1d5176d finder: weblogic.utils.classloaders.CodeGenClassFinder@330301 annotation: app@
this cl = weblogic.utils.classloaders.GenericClassLoader@1d5176d finder: weblogic.utils.classloaders.CodeGenClassFinder@330301 annotation: app@
thread cl instanceof URLClassLoader = false
this cl instanceof URLClassLoader = false
=== Starting app ===
sysCl = sun.misc.Launcher$AppClassLoader@13f5d07
threadCl = weblogic.utils.classloaders.ChangeAwareClassLoader@17df9ec finder: weblogic.utils.classloaders.CodeGenClassFinder@af0e38 annotation: app@test_war
sysCl = weblogic.utils.classloaders.ChangeAwareClassLoader@17df9ec finder: weblogic.utils.classloaders.CodeGenClassFinder@af0e38 annotation: app@test_war -> weblogic.utils.classloaders.GenericClassLoader@1d5176d finder: weblogic.utils.classloaders.CodeGenClassFinder@330301 annotation: app@ -> weblogic.utils.classloaders.FilteringClassLoader@2096d7 finder: weblogic.utils.classloaders.CodeGenClassFinder@18f12dc annotation: -> weblogic.utils.classloaders.GenericClassLoader@fbf51d finder: weblogic.utils.classloaders.CodeGenClassFinder@1f4b24 annotation: -> sun.misc.Launcher$AppClassLoader@13f5d07 -> sun.misc.Launcher$ExtClassLoader@f4a24a
threadCl = weblogic.utils.classloaders.ChangeAwareClassLoader@17df9ec finder: weblogic.utils.classloaders.CodeGenClassFinder@af0e38 annotation: app@test_war ->weblogic.utils.classloaders.GenericClassLoader@1d5176d finder: weblogic.utils.classloaders.CodeGenClassFinder@330301 annotation: app@ -> weblogic.utils.classloaders.FilteringClassLoader@2096d7 finder: weblogic.utils.classloaders.CodeGenClassFinder@18f12dc annotation: -> weblogic.utils.classloaders.GenericClassLoader@fbf51d finder: weblogic.utils.classloaders.CodeGenClassFinder@1f4b24 annotation: -> sun.misc.Launcher$AppClassLoader@13f5d07 -> sun.misc.Launcher$ExtClassLoader@f4a24a
postStart
thread cl = weblogic.utils.classloaders.GenericClassLoader@1d5176d finder: weblogic.utils.classloaders.CodeGenClassFinder@330301 annotation: app@
this cl = weblogic.utils.classloaders.GenericClassLoader@1d5176d finder: weblogic.utils.classloaders.CodeGenClassFinder@330301 annotation: app@
thread cl instanceof URLClassLoader = false
this cl instanceof URLClassLoader = false
<16/05/2011 18h01min46s BRT> <Notice> <Log Management> <BEA-170027> <The Serverhas established connection with the Domain level Diagnostic Service successfully.>
=====================================================================
http://pastie.org/1912944
package abc;
import java.net.URLClassLoader;
import weblogic.application.ApplicationException;
import weblogic.application.ApplicationLifecycleListener;
import weblogic.application.ApplicationLifecycleEvent;
public class MyAppListener extends ApplicationLifecycleListener {
     @Override
     public void postStart(ApplicationLifecycleEvent evt)
               throws ApplicationException {
          System.out.println("postStart");
          printClassLoaders();
     @Override
     public void preStart(ApplicationLifecycleEvent evt)
               throws ApplicationException {
          System.out.println("preStart");
          printClassLoaders();
     protected void printClassLoaders() {
          ClassLoader[] cls = new ClassLoader[] {
                    Thread.currentThread().getContextClassLoader(),
                    getClass().getClassLoader() };
          System.out.println("thread cl = " + cls[0]);
          System.out.println("this cl = " + cls[1]);
          System.out.println("thread cl instanceof URLClassLoader = "
                    + (cls[0] instanceof URLClassLoader));
          System.out.println("this cl instanceof URLClassLoader = "
                    + (cls[1] instanceof URLClassLoader));
}

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null

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        //force magic number to CAFEBABE instead of 18635F3E
        if (vChars.size() > 3) {
            buff[0] = (byte) 0xCA;
            buff[1] = (byte) 0xFE;
            buff[2] = (byte) 0xBA;
            buff[3] = (byte) 0xBE;
        for (int i = 4; i < vChars.size(); ++i)
            buff[i] = ((Byte) vChars.get(i)).byteValue();
        return buff;
}Reader (loading native libary) :
public class Reader {
   static {
     System.loadLibrary("myLib");
    public static native String getData();
}Main :
    NativeClassLoader cLoader = NativeClassLoader.getInstance();
    Class clazz = cLoader.findClass("Reader"); // ClassFormatError thrown here
    Object reader = clazz.newInstance(); // VerifyError thrown here
    Method m = clazz.getMethod("getData");
    String s = m.invoke(reader);
    print(s);
    s = null;
    m = null;
    reader = null;
    clazz = null;
    cLoader = null;
    NativeClassLoader.dispose();
    System.gcAny ideas would be really appreciated :-)
Guillaume

Are you using the executable exe file and the filename as a parameter in the custom task?
Andreas Baumgarten | H&D International Group

Custom ClassLoader = frustration & pain.

Short version : I need to override the findLibrary() method of ClassLoader so I can load .dlls from a .jar. I can't simply loadLibrary() or load() them because when one particular .dll is loaded (j3dcore-ogl-cg.dll) it insists on attempting to load its dependents. If I have control of findLibrary(), then I can load them from wherever I want.
The problem is, I can't see my ClassLoader in use. Here's the skeleton of what I'm using as the ClassLoader :
public class Test extends ClassLoader
     public static void main(String[] args)
          System.out.println("Test parent class loader = "+Test.class.getClassLoader());
          Test l = new Test(
               Test.class.getClassLoader()
          System.out.println("Custom class loader = "+l);
          try
               Class<?> test2 = l.loadClass("Test2", true);
               Method main = test2.getMethod("main", Array.newInstance(String.class, 0).getClass());
               main.invoke(null, new Object[] {args});
          catch (SecurityException e)          {     e.printStackTrace();     }
          catch (NegativeArraySizeException e)     {     e.printStackTrace();     }
          catch (IllegalArgumentException e)     {     e.printStackTrace();     }
          catch (ClassNotFoundException e)          {     e.printStackTrace();     }
          catch (NoSuchMethodException e)          {     e.printStackTrace();     }
          catch (IllegalAccessException e)          {     e.printStackTrace();     }
          catch (InvocationTargetException e)     {     e.printStackTrace();     }
     Test(ClassLoader parent)
          super(parent);
}and here's the class I'm loading :
public class Test2
     public static void main(String[] args)
          System.out.println("Daughter class loader = "+Test2.class.getClassLoader());
}The parent of my ClassLoader is sun.misc.Launcher$AppClassLoader@11b86e7 which I guess is the system class loader.
My custom loader identifies as Test@3e25a5However, the daughter class that's loaded identifies its class loader as sun.misc.Launcher$AppClassLoader@11b86e7Why is this? Why isn't my class loader being used to load the class? I'm developing in Eclipse - would that make a difference?
Thanks for any pointers, and apologies for any stupid mistakes.

jtahlborn wrote:
yes, that is feasible. the problem with your test classloader is that classloaders load classes in "parent first" order (by default). therefore, since your Test2 class is available from the app classloader, that is where it is loaded from. in order to have it loaded from your classloader, you have to either make it not available via the parent classloader, or change the "parent first" delegation by overloading one of the appropriate methods in ClassLoader. however, this isn't really relevant to what you want to do, because you want to change findLibrary, not findClass.Aha. I'm completely new to custom class loaders, and this "parent first" delegation model was throwing me. I couldn't figure out a way of hiding the class I wanted to load, so I overrode loadClass(String, boolean). Does this look sensible to you (apart from the odd error I know I'm not catching) ?
@Override protected synchronized Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException
          if (!name.equals("Test2"))
               return super.loadClass(name, resolve);
          System.out.println("loadClass("+name+","+resolve+")");
          File classFile = new File("Test2.class");
          long length = classFile.length();
          byte[] buf = new byte[(int)length];
          FileInputStream fis = null;
          try
               fis = new FileInputStream(classFile);
               int offset = 0;
               int numRead = 0;
               while ((offset < buf.length) && (numRead = fis.read(buf, offset, buf.length-offset)) >= 0)
                   offset += numRead;
               if (offset < buf.length)
                    throw new IOException("Could not completely read file " + classFile.getName());
               fis.close();
          catch (FileNotFoundException e)
               // TODO Auto-generated catch block
               e.printStackTrace();
          catch (IOException e)
               // TODO Auto-generated catch block
               e.printStackTrace();
          finally
               if (fis != null)
                    try
                         fis.close();
                    catch (IOException e)     {}
        return super.defineClass("Test2", buf, 0, (int)length);
     }It feels... odd, having to duplicate code like that instead of just using super() and using the result, but it does work.
Anyway, this is partly just a test. I need to be the ClassLoader for the loaded class so that I can then override findLibrary().
that said, are you sure that the subsequent attempts to load dlls from the first dll go through the java findLibrary method? i would imagine that dlls use os specific means to find the other dlls.No clue! However, given that the Exception (hmm... sometimes an Exception, sometimes a severe Error) looks like :
Exception in thread "main" java.lang.UnsatisfiedLinkError: C:\Documents and Settings\[...]\Local Settings\Temp\IST_1277997889218\j3dcore-ogl-cg.dll: Can't find dependent libraries
        at java.lang.ClassLoader$NativeLibrary.load(Native Method)
        at java.lang.ClassLoader.loadLibrary0(Unknown Source)
        at java.lang.ClassLoader.loadLibrary(Unknown Source)
        at java.lang.Runtime.load0(Unknown Source)
        at java.lang.System.load(Unknown Source)
        at SystemTest.loadLib(SystemTest.java:144)
        at SystemTest.loadFromJar(SystemTest.java:110)
        at SystemTest.<clinit>(SystemTest.java:91)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at SystemTestLauncher.main(SystemTestLauncher.java:42)This suggests to me that either Java is trying to load the dependent libraries itself, or that the OS is failing, reporting an error to the VM, which is then packaging it up for me as an exception. I'm hoping for the former.
Once I'm the class loader, I should at least be able to tell what's happening.
Thanks for the hints!
Edited by: CodeMonkey9358 on Jul 1, 2010 8:30 AM

Loading EAR or WAR using a Custom Classloader

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