JBossDeveloper

Good.

Of course two thing had to be made: injecting user classpath
and container's classloader

Well done Mr Chiba ! It works ... except for the classpath of course, but it doesn't matter in my app, I can manage it.

Hi ,

I know that it is not the right place to ask this question but I'm sure you've got the solution.

I'd like to know if it is possible to load a class that is already loaded or to remove from the classloader a loaded class ?

Indeed, I've got 3 classes with the same name and prototypes (methods ...) but not in the same package.
So I'd like to load the class dynamically, depends on a property files which inform the package.
So, the first time I load class a.Bat (and change the name to b.Bat), it works. But the next time, if I try to load c.Bat, I've got an LinkageError, which means that the class is already loaded, BUT i don't need the loaded class anymore.

Thanks for your suggestion, and sorry again to post it here.

I'd like to know if it is possible to load a class that is already
loaded or to remove from the classloader a loaded class ?

However, I cannot understand why you got LinkageError when you
loaded c.Bat. Is "c" a package name? If yes, c.Bat is a different class
from a.Bat and b.Bat. I suppose that your program (a.Bat or b.Bat)
accidentally had been linked with an older version of c.Bat.

Here is my ClassLoader :

package loader;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;

/**
 * @author Batoussa Mougamadou
 */
public class MyClassLoader extends ClassLoader {

 private final ClassPool originalPool = ClassPool.getDefault();
 ////////////////

 public String getPackage() {
 try {
 FileInputStream in = new FileInputStream("file.properties");
 Properties prop = new Properties();

 // load all
 prop.load(in);

 in.close();
 return prop.getProperty("package");
 } catch (Exception e) {
 e.printStackTrace();
 return null;
 }
 }

 public Class loadClass(String className, boolean resolveIt)
 throws ClassNotFoundException {
 return super.loadClass(className, resolveIt);
 }

 private Class loadClass(byte[] b, String className) {
 //override classDefine (as it is protected) and define the class.
 Class clazz = null;
 try {
 ClassLoader loader = ClassLoader.getSystemClassLoader();

 Class cls = Class.forName("java.lang.ClassLoader");

 // CALL FIND LOADED CLASS
 java.lang.reflect.Method method =
 cls.getDeclaredMethod("findLoadedClass", new Class[] { String.class });
 method.setAccessible(true);
 Object[] args = new Object[] { className };
 clazz = (Class) method.invoke(loader, args);
 method.setAccessible(false);

 if( clazz != null )
 return clazz;
 else System.out.println("CLASS NOT BEEN LOADED");

 // CALL DEFINE CLASS
 method = cls.getDeclaredMethod( "defineClass", new Class[] { String.class, byte[].class, int.class, int.class });

 // protected method invocaton
 method.setAccessible(true);
 args = new Object[] { className, b, new Integer(0), new Integer(b.length)};
 clazz = (Class) method.invoke(loader, args);
 method.setAccessible(false);

 } catch (Exception e) {
 e.printStackTrace();
 System.exit(1);
 }
 return clazz;
 }

 private ClassPool pool;

 public MyClassLoader() throws NotFoundException {
 pool = new ClassPool();
 pool.insertClassPath("."); // MyApp.class must be there.
 }

 /* Finds a specified class.
 * The bytecode for that class can be modified.
 */
 public Class findClass(String name) throws ClassNotFoundException {
 try {
 // Set the class path
 pool.appendClassPath("C:/Program Files/eclipse/workspace/WebClassLoader/WEB-INF/lib/bat.jar");
 CtClass cc = pool.get(getPackage()+"."+name);
 // Change the name of the class
 cc.setName("b." + name);
 return loadClass(cc.toBytecode(), "b." + name);
 } catch (NotFoundException e) {
 throw new ClassNotFoundException();
 } catch (IOException e) {
 throw new ClassNotFoundException();
 } catch (CannotCompileException e) {
 throw new ClassNotFoundException();
 }
 }
}

Maybe the only solution is to use JPDA.

Otherwise, if feasible, you should make
a new child class loader for loading your app.
and reload your app. from scratch
whenever the config file is updated.
However, this solution discards all existing objects
when the config is updated.