Java - Dynamically loading classes

Question

I'm currently creating a plugin system (My first attempt), looking at other peoples code I'm trying to piece together my own classloader and get the plugins loaded from a directory (These will be class files)

My problem is that whenever I attempt to load the class with my classloader, any imports in the plugin referencing the program are not found by the classloader. (ie: MyClass extends Plugin, com.mgmc.plugins noclassdeffound) Different namespace?

Some sample code: Classloader:

/*


* To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package com.mcgm.game.provider;

import com.mcgm.utils.Misc;
import com.mcgm.utils.Paths;
import java.awt.AWTPermission;
import java.io.*;
import java.net.MalformedURLException;
import java.net.SocketPermission;
import java.net.URL;
import java.security.CodeSigner;
import java.security.CodeSource;
import java.security.Permissions;
import java.security.ProtectionDomain;
import java.util.PropertyPermission;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Tom
 */
public class GameClassLoader extends ClassLoader {
private final ProtectionDomain domain;
private final URL base;

public GameClassLoader(final URL url) {
    base = url;
    final CodeSource codeSource = new CodeSource(base, (CodeSigner[]) null);
    domain = new ProtectionDomain(codeSource, getPermissions());
}

public void loadGames() {
    for (File f : Paths.compiledFolder.listFiles()) {
        try {
            Class c = loadClass(f.getPath());
            Misc.outPrint(c.getName());
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(GameClassLoader.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

private Permissions getPermissions() {
    final Permissions ps = new Permissions();
    ps.add(new AWTPermission("accessEventQueue"));
    ps.add(new PropertyPermission("user.home", "read"));
    ps.add(new PropertyPermission("java.vendor", "read"));
    ps.add(new PropertyPermission("java.version", "read"));
    ps.add(new PropertyPermission("os.name", "read"));
    ps.add(new PropertyPermission("os.arch", "read"));
    ps.add(new PropertyPermission("os.version", "read"));
    ps.add(new SocketPermission("*", "resolve"));
    ps.add(new FilePermission(Paths.compiledFolder.getPath(), "read,write,delete"));
    ps.setReadOnly();
    return ps;
}

@Override
@SuppressWarnings("rawtypes")
public Class<?> loadClass(final String name, final boolean resolve) throws ClassNotFoundException {
    Class clazz = findLoadedClass(name);

    if (clazz == null) {
        try {
            byte[] bytes = loadClassData(name);
            clazz = defineClass(name, bytes, 0, bytes.length, domain);
            if (resolve) {
                resolveClass(clazz);
            }
        } catch (final Exception e) {
            clazz = super.loadClass(name, resolve);
        }
    }

    return clazz;
}

public byte[] loadClassData(final String name) {
    try {
        final InputStream in = getResourceAsStream(name.replace('.', '/') + ".class");
        final byte[] buffer = new byte[4096];
        final ByteArrayOutputStream out = new ByteArrayOutputStream();
        int n;
        while ((n = in.read(buffer, 0, 4096)) != -1) {
            out.write(buffer, 0, n);
        }
        return out.toByteArray();
    } catch (IOException ex) {
        Logger.getLogger(GameClassLoader.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;

}

@Override
public URL getResource(final String name) {
    try {
        return new URL(base, name);
    } catch (final MalformedURLException e) {
        return null;
    }
}

@Override
public InputStream getResourceAsStream(final String name) {
    try {
        return new URL(base, name).openStream();
    } catch (final IOException e) {
        return null;
    }
}
}

The Plugin I am loading: (The annotation isn't found either)

import com.mcgm.GameInfo;
import com.mcgm.game.Minigame;
  @GameInfo(name = "RandomGame",
description = "A really long and boring game.",
authors = {"Tom", "Is", "The", "Greatest"},
version = 0.1,
maxPlayers = 100,
teamBased = false,
teamAmount = -1,
PvP = false)
public class game extends Minigame {
}

How I'm calling the class to be loaded:

  GameClassLoader classLoader = new GameClassLoader(Paths.compiledFolder.toURI().toURL());
            classLoader.loadClass("game", true);

I figure this is trivial for those that know what they're doing!

Answer 1

FINALLY! After a day and a half of searching, Vulcan pointed me in the right direction: I changed the GameClassLoader to:

public GameClassLoader(final URL url, ClassLoader parent) {
    super(parent);

and finally added the base url to the getResourceAsStream()

final InputStream in = getResourceAsStream(base.getFile() + "/" + name.replace('.', '/') + ".class");

Thanks so much for your help guys!

Answer 2

Try to add leading slash into resource path: final InputStream in = getResourceAsStream("/" + name.replace('.', '/') + ".class");

This is the thing I have to try every time I am calling getResourceAsStream() . I just have tried this for you again. The path here is relative to package of class that is used to call getResourceAsStream() , so leading slash is needed to say "start from root."