Intercepting Filter模式

Intercepting Filter设计模式，在Web曾处理前进行过滤。一种很有用的过滤是用户是否登陆的安全性检查。即在以下的doFilter函数中添加安全性检查的语句，这样就不需要对每个页面（servlet）进行安全性配置。

通常通过实现javax.servlet.Filter接口实现，其主要方法有：

Method Summary
void	destroy()           Called by the web container to indicate to a filter that it is being taken out of service.
void	doFilter(ServletRequest request, ServletResponse response, FilterChain chain)           The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain.
void	init(FilterConfig filterConfig)           Called by the web container to indicate to a filter that it is being placed into service.

然后在web.xml中配置过滤器即可。