1. 实现你自己的ClassLoader, 给这个loader加listener

2. listener监听loaded的文件last update time 属性来触发管理终止实例的事件

3. 终止实例以后, 把旧的loaded的class文件clear掉, 重新调用一次新的文件.

难点是在于怎样处理已经实例化的Class的引用, 统一终止掉?

在做某些server的应用中才会有这样的需求吧?

你可以参考一下resin和phoenix源代码, 它们都有Plug and Play的功能的.

至于ClassLoader，是否有详细的资料？

这个是ClassLoader javadoc的link:

http://java.sun.com/j2se/1.4.1/docs/api/java/lang/ClassLoader.html

希望对你有用, good luck with your project.

Quake is right on the point about classloader, what we did here is throw exception if old instance is still refereneced. Sorry can't give you the code as it's not my own, but it's very basic once you read the jdk doc.