不停止JVM動態更新Java類

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不停止JVM動態更新Java類，到底有什麼用處？

對於大多數WEB程序這個功能並沒有什麼意義，這裏假設在桌面系統以及服務器的情況：

1. 桌面軟件，當用戶在線升級程序後，需要將最新的Java類動態提取到當前的classloader以供用戶使用最新狀態的程序
2. 桌面軟件，當需要各種插件時，需要從設定文件中提取信息，並在啓動時提取。而這種提取需要在程序啓動之後，例如Eclipse
3. Servlet容器，動態提取最新狀態的jar包、Servlet類、JSP類以及設定文件等

不停止JVM動態更新Java類功能，顯然在很多地方是必不可少的。以下筆者將以代碼的形勢演示如何實現此功能。

代碼：

package org.logical_paradox.reloader; import java.io.File; import java.lang.reflect.Method; import java.net.URL; import java.net.URLClassLoader; /** * @author satoshi akabane * @version $Revision$ */ public class Reloader { public static final String REPOSITORY = "./lib/"; private Reloader() { } public static final void main(String[] args) throws Exception { Reloader reloader = new Reloader(); ClassLoader current = Thread.currentThread().getContextClassLoader(); // v1 log("HelloWorldLogic_v1 is now loading."); ClassLoader loader = reloader.load(REPOSITORY + "HelloWorldLogic_v1.jar"); Thread.currentThread().setContextClassLoader(loader); // switch context class loader Object objv1 = loader.loadClass("HelloWorldLogic").newInstance(); Method method = objv1.getClass().getMethod("getHello", new Class[0]); // getHello() Object msg = method.invoke(objv1, new Object[0]); log("answer from v1 is [" + msg.toString() + "]"); // v2 loader = null; log("HelloWorldLogic_v2 is now loading."); loader = reloader.load(REPOSITORY + "HelloWorldLogic_v2.jar"); Thread.currentThread().setContextClassLoader(loader); // switch context class loader Object objv2 = loader.loadClass("HelloWorldLogic").newInstance(); method = objv2.getClass().getMethod("getHello", new Class[0]); // getHello() msg = method.invoke(objv2, new Object[0]); log("answer from v2 is [" + msg.toString() + "]"); Thread.currentThread().setContextClassLoader(current); } private static final void log(String msg) { System.out.println("log: " + msg); } private URLClassLoader load(String jarname) throws Exception { final String base = (new File(jarname).getCanonicalFile().toURL()).toString(); URL url = new URL("jar:" + base + "!/"); URLClassLoader loader = new URLClassLoader(new URL[]{url}); return loader; } }

 

 

執行結果：

[java] log: HelloWorldLogic_v1 is now loading. [java] log: answer from v1 is [version 1] [java] log: HelloWorldLogic_v2 is now loading. [java] log: answer from v2 is [version 2]

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轉貼請註明出處：http://blog.csdn.net/froole