Loading jar at runtime using custom classloader

Hi,
I'm trying to load a jar file to an application running inside weblogic at runtime.
I followed the example that was posted at
http://dev2dev.bea.com/cs/user/blog?file=/blog/jcscoobyrs/archive/2005/05/realworld_use_f.html
and did the following:
URLClassLoader loader = null;
URL[] urls = {new URL("file:///" + "C:/Program Files/aaa/WEB-INF/lib/ImportTest3.jar")};
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
ClassLoader loader = new URLClassLoader(urls, classLoader);
Thread.currentThread().setContextClassLoader(loader);
Class customClass = Class.forName(className, true, loader);
customCode = customClass.newInstance();
Thread.currentThread().setContextClassLoader(classLoader);
everything works fine when I access my application once.
But when I'm trying to do the same again, everything fails.
Any ideas?
Thanks!

When you say everything fails - can you clarify the failure? Can you paste the stacktrace? Is it a ClassNotFoundException?

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1. Compile Test.java file and have it encrypted, make it into a jar file - test.jar.
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.............. (loading several system classes)
load class: com.sun.tools.javac.util.Position
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null

I don't know why he was specifying the javac classpath like that instead of using javac's -classpath option.
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I'm doing something very similar. In fact my launcher is also stored in launcher.jar. It will start any application on the classpath and load dependencies jars located in the specified directory.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Guillaume

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

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Hi Friends,
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          pt = ptClass.newInstance();
          Method ptStart = ptClass.getMethod("start", new Class[0]);
          ptStart.invoke(pt, new Object[0]);
          return true;
     } catch(Exception e) {
          return false;
}I also have a method to shut down the server:
private boolean stopProxy() {
     try {
          Class ptClass = pl.loadClass("proxy.POPThread");
          Method ptInterrupt = ptClass.getMethod("interrupt", new Class[0]);
          ptInterrupt.invoke(pt, new Object[0]);
          return true;
     } catch(Exception e) {
          return false;
}These appear to be working fine, the problem I have however is when I try to rename the existing jar file (proxy.jar) in order to replace it with a new one (proxy.new), the renameTo method on the File object fails. I am guessing that is because the proxy.jar file is still in use by the JVM. I have tried setting the classloader var to null, but this doesnt seem to have any effect.
My main question is how can I 'free' the jar file so that it can be replaced with new code? Is it possible? My only otherway of working around this is to have a variable stored in a file pointing at the 'current' code, but the jar file isn't litterally replaced.
This is a standalone application, which will probably run in a startup script on a server, so webstart isn't really an option.
TIA
iklesteve

I have found this to be true anytime I try to use the renameTo() API to rename a file with a .jar file extension (regardless of the actual file type - i.e. it could be a text file with .jar appended and it will still fail) in the case where the class making the renameTo() call is loaded from another .jar file.
I run the same exact code after extracting from the .jar, then the rename to the other .jar file is successful. Also, if I rename the .jar file to a ".ja" file, I can successfully rename the jar file even if the code is running with the context of another .jar file.
Is this some kind of bogus security measure within the JVM or is it a bug?

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));
}

Detecting when exception was thrown using custom class loader

Hello all,
I would like to implement the solution described here - http://stackoverflow.com/questions/75218/how-can-i-detect-when-an-exceptions-been-thrown-globally-in-java - that uses custom class loader in order to detect when an Exeption thrown somewhere in the JVM hosting my app, please note that exceptions might be thrown from 3rd party jars the app is using. So, thanks to help I got from another post, I've managed to code the custom class loader. My question is how can the class loader wrap the original exception, as the methods in ClassLoader deals with classes, not instances. So where should I set the original exception?
Thanks!
Edited by: user9355666 on Sep 28, 2010 10:48 PM

user9355666 wrote:
I think I'm missing something fundumental, forgive me for being slow...
This is what I did so far. For the exception wrapper I made a simple class extens Exception that recieve Exception in its ctor and store it. I also subclassed ClassLoader and override its loadClass(). I've registered it as the system classloader. My thinking was to check in that point that if the requested class is instance of Exception and if yes, returning my wrapper class wrapping this exception. But, since loadClass() return class, how can I set in the wrapper the original exception?
In addition, let's say 2 different places in the code throws NPE, to my understanding the classloader will load NPE only once, so how throwing the NPE in the second time can be detected?you are missing a key point. you should creating a custom implementation of the NPE class which hooks into your detection code in its constructor. from that point forward, anytime any NPE (which is your custom class) is constructed, you can detect it.

Loading jar at runtime using custom classloader

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