Java -动态加载类

Question

我目前正在创建一个插件系统(我的第一次尝试)，查看其他人的代码，我试图拼凑我自己的类加载器，并从一个目录中加载插件(这些将是类文件)

我的问题是，每当我试图用我的类加载器加载类时，类加载器都找不到引用程序的插件中的任何导入。(例如: MyClass扩展插件，com.mgmc.plugins无类定义)不同的命名空间？

一些示例代码: 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;
    }
}
}

我正在加载的插件：(注释也没有找到)

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 {
}

我如何调用要加载的类：

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

我认为这对于那些知道自己在做什么的人来说是微不足道的！

Answer 1

终于来了！经过一天半的搜索，瓦肯给我指明了正确的方向:我将GameClassLoader改为：

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

并最终将基本url添加到getResourceAsStream()

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

非常感谢你们的帮助！

Answer 2

尝试在资源路径中添加前导斜杠：final InputStream in = getResourceAsStream("/" + name.replace('.', '/') + ".class");

这是我每次调用getResourceAsStream()时都要尝试的事情。我只是为你再试了一次。这里的路径是相对于用于调用getResourceAsStream()的类包的路径，因此需要使用前导斜杠来表示“从根开始”。