[英]Java - Dynamically loading classes
我当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,我试图将自己的类加载器拼凑在一起,并从目录中加载插件(这些将是类文件)
我的问题是,每当尝试使用类加载器加载类时,类加载器都找不到插件中引用程序的任何导入。 (即:MyClass扩展插件,com.mgmc.plugins noclassdeffound)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:(也未找到注释)
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!
最后! 经过一天半的搜索,Vulcan向我指出了正确的方向:我将GameClassLoader更改为:
public GameClassLoader(final URL url, ClassLoader parent) {
super(parent);
最后将基本网址添加到getResourceAsStream()
final InputStream in = getResourceAsStream(base.getFile() + "/" + name.replace('.', '/') + ".class");
非常感谢您的帮助!
尝试将斜杠添加到资源路径中: final InputStream in = getResourceAsStream("/" + name.replace('.', '/') + ".class");
这是我每次调用getResourceAsStream()
时都必须尝试的事情。 我只是再次为您尝试过。 此处的路径是相对于用于调用getResourceAsStream()
的类的包而言的,因此需要用斜杠表示“从根开始”。
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