jar包的调用，类似C++的DLL调用

我们大家都知道，每个运行中的线程都有一个成员contextClassLoader，用来在运行时动态地载入其它类。

系统默认的contextClassLoader是systemClassLoader，所以一般而言java程序在执行时可以使用JVM自带的类、$JAVA_HOME/jre/lib/ext/中的类和$CLASSPATH/中的类，对于非默认的jar，一般只能手动在配置环境添加。

但事实上，我们可以通过Thread.currentThread().setContextClassLoader()更改当前线程的contextClassLoader行为，实现在程序内加载外部jar。

PS:
ClassLoader的工作原理是：
1) 线程需要用到某个类时，contextClassLoader将被请求来载入该类
2) contextClassLoader请求它的父ClassLoader来完成该载入请求
3) 如果父ClassLoader无法载入类，则contextClassLoader试图自己来载入

 

package org.loon.framework.jar;/** *//** * <p>Title: LoonFramework</p> * <p>Description:JarLoader，用于jar包的外部操作</p> * <p>Copyright: Copyright (c) 2007</p> * <p>Company: LoonFramework</p> * @author chenpeng * @email：[e-mail] * @version 0.1 */import java.io.BufferedInputStream;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.lang.reflect.Method;import java.net.MalformedURLException;import java.net.URL;import java.util.ArrayList;import java.util.HashMap;import java.util.Hashtable;import java.util.jar.JarEntry;import java.util.jar.JarInputStream;import java.util.jar.Manifest;public class JarLoader extends ClassLoader { //资源缓存 public static Hashtable resources = new Hashtable(); public static JarLoader loader = new JarLoader(); public static Class load(byte[] resource) throws Exception { // 主函数所在类全称 String mainClassName = ""; //class资源及实体缓存 ArrayList classNames = new ArrayList(); ArrayList classBuffers = new ArrayList(); // 存储依赖类 HashMap depends = new HashMap(); // 将byte[]转为JarInputStream JarInputStream jar = new JarInputStream(new ByteArrayInputStream( resource)); Manifest manifest = jar.getManifest(); // 当Main-Class被声明时,获得主函数所在类全称 if (manifest != null) { mainClassName = manifest.getMainAttributes().getValue("Main-Class"); } // 依次获得对应JAR文件中封装的各个被压缩文件的JarEntry JarEntry entry; while ((entry = jar.getNextJarEntry()) != null) { // 当找到的entry为class时 if (entry.getName().toLowerCase().endsWith(".class")) { // 将类路径转变为类全称 String name = entry.getName().substring(0, entry.getName().length() - ".class".length()).replace( '/', '.'); // 加载该类 byte[] data = getResourceData(jar); // 缓存类名及数据 classNames.add(name); classBuffers.add(data); } else { // 非class结尾但开头字符为'/'时 if (entry.getName().charAt(0) == '/') { resources.put(entry.getName(), getResourceData(jar)); // 否则追加'/'后缓存 } else { resources.put("/" + entry.getName(), getResourceData(jar)); } } } //当获得的main-class名不为空时 while (classNames.size() > 0) { //获得类路径全长 int n = classNames.size(); for (int i = classNames.size() - 1; i >= 0; i--) { try { //查询指定类 loader.defineClass((String) classNames.get(i), (byte[]) classBuffers.get(i), 0, ((byte[]) classBuffers.get(i)).length); //获得类名 String pkName = (String) classNames.get(i); if (pkName.lastIndexOf('.') >= 0) { pkName = pkName .substring(0, pkName.lastIndexOf('.')); if (loader.getPackage(pkName) == null) { loader.definePackage(pkName, null, null, null, null, null, null, null); } } //查询后删除缓冲 classNames.remove(i); classBuffers.remove(i); } catch (NoClassDefFoundError e) { depends.put((String) classNames.get(i), e.getMessage() .replaceAll("/", ".")); } catch (UnsupportedClassVersionError e) { //jre版本错误提示 throw new UnsupportedClassVersionError(classNames.get(i) + ", " + System.getProperty("java.vm.name") + " " + System.getProperty("java.vm.version") + ")"); } } if (n == classNames.size()) { for (int i = 0; i < classNames.size(); i++) { System.err.println("NoClassDefFoundError:" + classNames.get(i)); String className = (String) classNames.get(i); while (depends.containsKey(className)) { className = (String) depends.get(className); } } break; } } try { //加载 Thread.currentThread().setContextClassLoader(loader); // 获得指定类,查找其他类方式相仿 return Class.forName(mainClassName, true, loader); } catch (ClassNotFoundException e) { String className = mainClassName; while (depends.containsKey(className)) { className = (String) depends.get(className); } throw new ClassNotFoundException(className); } } /** *//** * 获得指定路径文件的byte[]形式 * @param name * @return */ final static public byte[] getDataSource(String name) { FileInputStream fileInput; try { fileInput = new FileInputStream(new File(name)); } catch (FileNotFoundException e) { fileInput = null; } BufferedInputStream bufferedInput = new BufferedInputStream(fileInput); return getDataSource(bufferedInput); } /** *//** * 获得指定InputStream的byte[]形式 * @param name * @return */ final static public byte[] getDataSource(InputStream is) { if (is == null) { return null; } ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); byte[] arrayByte = null; try { byte[] bytes = new byte[8192]; bytes = new byte[is.available()]; int read; while ((read = is.read(bytes)) >= 0) { byteArrayOutputStream.write(bytes, 0, read); } arrayByte = byteArrayOutputStream.toByteArray(); } catch (IOException e) { return null; } finally { try { if (byteArrayOutputStream != null) { byteArrayOutputStream.close(); byteArrayOutputStream = null; } if (is != null) { is.close(); is = null; } } catch (IOException e) { } } return arrayByte; } /** *//** * 获得指定JarInputStream的byte[]形式 * @param jar * @return * @throws IOException */ final static private byte[] getResourceData(JarInputStream jar) throws IOException { ByteArrayOutputStream data = new ByteArrayOutputStream(); byte[] buffer = new byte[8192]; int size; while (jar.available() > 0) { size = jar.read(buffer); if (size > 0) { data.write(buffer, 0, size); } } return data.toByteArray(); } /** *//** * 重载的getResource,检查是否重复包含 */ public URL getResource(String name) { if (resources.containsKey("/" + name)) { try { return new URL("file:///" + name); } catch (MalformedURLException e) { e.printStackTrace(); } } return super.getResource(name); } /** *//** * 执行指定class类 * @param clz * @param methodName * @param args */ public static void callVoidMethod(Class clz, String methodName, String[] args) { Class[] arg = new Class[1]; arg[0] = args.getClass(); try { Method method = clz.getMethod(methodName, arg); Object[] inArg = new Object[1]; inArg[0] = args; method.invoke(clz, inArg); } catch (Exception e) { System.err.println(e.getMessage()); } } /** *//** * 重载的getResourceAsStream,检查是否重复包含 */ public InputStream getResourceAsStream(String name) { if (name.charAt(0) == '/') { name = name.substring(1); } if (resources.containsKey("/" + name)) { return new ByteArrayInputStream((byte[]) resources.get("/" + name)); } return super.getResourceAsStream(name); }}

 

运行示例：
package org.loon.framework.jar;/** *//** * <p> * Title: LoonFramework * </p> * <p> * Description:从外部启动jar包 * </p> * <p> * Copyright: Copyright (c) 2007 * </p> * <p> * Company: LoonFramework * </p> * * @author chenpeng * @email：[e-mail] * @version 0.1 */public class JarTest { public static void main(String[] args) { //将jar包转为byte[] byte[] resource = JarLoader.getDataSource("D:/fps_test.jar"); try { //通过byte[]获得主函数所在类 Class clz = JarLoader.load(resource); //调用main函数 JarLoader.callVoidMethod(clz, "main", new String[] {""}); } catch (Exception e) { e.getStackTrace(); } }}

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/cping1982/archive/2007/11/12/1880490.aspx