分析LogFilter

package lee;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.*;

/**
* Description:
* <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
* <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
* <br/>This program is protected by copyright laws.
* <br/>Program Name:
* <br/>Date:
* @author Yeeku.H.Lee kongyeeku@163.com
* @version 1.0
*/

@WebFilter(filterName="log"
,urlPatterns={"/*"})
public class LogFilter implements Filter
{
// FilterConfig可用于访问Filter的配置信息
private FilterConfig config;
// 实现初始化方法
public void init(FilterConfig config)
{
this.config = config;
}
// 实现销毁方法
public void destroy()
{
this.config = null;
}
// 执行过滤的核心方法
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
throws IOException,ServletException
{
// ---------下面代码用于对用户请求执行预处理---------
// 获取ServletContext对象，用于记录日志
ServletContext context = this.config.getServletContext();
long before = System.currentTimeMillis();
System.out.println("开始过滤...");
// 将请求转换成HttpServletRequest请求
HttpServletRequest hrequest = (HttpServletRequest)request;
// 输出提示信息
System.out.println("Filter已经截获到用户的请求的地址： " +
hrequest.getServletPath());
// Filter只是链式处理，请求依然放行到目的地址
chain.doFilter(request, response);
// ---------下面代码用于对服务器响应执行后处理---------
long after = System.currentTimeMillis();
// 输出提示信息
System.out.println("过滤结束");
// 输出提示信息
System.out.println("请求被定位到" + hrequest.getRequestURI() +
" 所花的时间为: " + (after - before));
}
}