logFilter Analysis

分析下面这段代码：
 public void doFilter(ServletRequest request,
    ServletResponse response, FilterChain chain) throws IOException, ServletException {
        //--------下面的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...");
        //将请求转换为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);
        long after = System.currentTimeMillis();
        System.out.println("请求被定位到"+hRequest.getRequestURI()+" 所花时间为："+(after-before));
　　　　}
　　
　

• getServletPath()用户的请求地址
• getRequestURI()请求的url路径，例如此处的答应信息为/{应用名}/demo.jsp
• HttpServletRequest hRequest = (HttpServletRequest) request;　  将请求转换为HttpServletRequest请求
• ServletContext context=this.config.getServletContext();  获取ServletContext对象，用于记录日志