用反射解析jar文件并执行里面Java代码

1、使用JarFile类读取jar包MANIFEST.MF中的Main-Class，如果没有设置Main-Class则调用方法中指定执行函数

2、解压jar文件

3、设置classPath

4、利用反射取得class和method，并运行该method

如下代码Run.java将被打包到jar文件中，使用Maven构建并打包：

 

package com.chenzehe.runjar;
public class Run {
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		System.out.println("run......");
		if (args.length > 0) {
			System.out.println("args: " + args[0]);
		}
	}
}

 

开始打包没有指定在MANIFEST.MF中指定Main-Class，下面运行时只能指定要运行的类。

 RunJar.java为解析并执行该jar文件方法的类：

 

package com.chenzehe.runjar;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Array;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

public class RunJar {

	/**
	 * @param args
	 */
	public static void main(String[] args) throws Throwable {
		String usage = "RunJar jarFile [mainClass] args...";

		if (args.length < 1) {
			System.err.println(usage);
			System.exit(-1);
		}
		int firstArg = 0;
		String fileName = args[firstArg++];
		File file = new File(fileName);

		// 从jar文件MANIFEST.MF中读取Main-Class
		String mainClassName = null;
		JarFile jarFile;
		try {
			jarFile = new JarFile(fileName);
		} catch (IOException io) {
			throw new IOException("Error opening job jar: " + fileName)
					.initCause(io);
		}

		Manifest manifest = jarFile.getManifest();
		if (manifest != null) {
			mainClassName = manifest.getMainAttributes().getValue("Main-Class");
		}
		jarFile.close();

		if (mainClassName == null) {
			if (args.length < 2) {
				System.err.println(usage);
				System.exit(-1);
			}
			// 如果MANIFEST.MF未设置Main-Class,则用户输入
			mainClassName = args[firstArg++];
		}
		mainClassName = mainClassName.replaceAll("/", ".");
		final File workDir = File.createTempFile("unjar", "",
				new File(System.getProperty("user.dir")));
		workDir.delete();
		workDir.mkdirs();
		if (!workDir.isDirectory()) {
			System.err.println("Mkdirs failed to create " + workDir);
			System.exit(-1);
		}

		// 解压jar文件
		unJar(file, workDir);

		// 设置classPath
		ArrayList<URL> classPath = new ArrayList<URL>();
		classPath.add(new File(workDir + "/").toURL());
		classPath.add(file.toURL());
		ClassLoader loader = new URLClassLoader(classPath.toArray(new URL[0]));
		Thread.currentThread().setContextClassLoader(loader);

		// 利用反射取得class和method
		Class<?> mainClass = Class.forName(mainClassName, true, loader);
		Method main = mainClass.getMethod("main", new Class[] { Array
				.newInstance(String.class, 0).getClass() });
		String[] newArgs = Arrays.asList(args).subList(firstArg, args.length)
				.toArray(new String[0]);
		try {
			// 运行方法
			main.invoke(null, new Object[] { newArgs });
		} catch (InvocationTargetException e) {
			throw e.getTargetException();
		}
	}
        //解压jar包中的文件到toDir目录
	public static void unJar(File jarFile, File toDir) throws IOException {
		JarFile jar = new JarFile(jarFile);
		try {
			Enumeration entries = jar.entries();
			while (entries.hasMoreElements()) {
				JarEntry entry = (JarEntry) entries.nextElement();
				if (!entry.isDirectory()) {
					InputStream in = jar.getInputStream(entry);
					try {
						File file = new File(toDir, entry.getName());
						if (!file.getParentFile().mkdirs()) {
							if (!file.getParentFile().isDirectory()) {
								throw new IOException(
										"Mkdirs failed to create "
												+ file.getParentFile()
														.toString());
							}
						}
						OutputStream out = new FileOutputStream(file);
						try {
							byte[] buffer = new byte[8192];
							int i;
							while ((i = in.read(buffer)) != -1) {
								out.write(buffer, 0, i);
							}
						} finally {
							out.close();
						}
					} finally {
						in.close();
					}
				}
			}
		} finally {
			jar.close();
		}
	}
}

 

该代码为Hadoop中job提交到服务器调用的代码RunJar。

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