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!
Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time. Dynamic class loading is done when the name of the class is not known at compile time.
A class is always identified using its fully qualified name (package. classname). So when a class is loaded into JVM, you have an entry as (package, classname, classloader). Therefore the same class can be loaded twice by two different ClassLoader instances.
In order to actually load a class, the JVM uses Classloader objects. Every already loaded class contains a reference to its class loader, and that class loader is used to load all the classes referenced from that class.
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!
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With