WebFilter

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package test.filter;        import javax.servlet.Filter;   import javax.servlet.FilterChain;   import javax.servlet.FilterConfig;   import javax.servlet.ServletContext;   import javax.servlet.ServletRequest;   import javax.servlet.ServletResponse;   import javax.servlet.http.HttpServletRequest;        public class LogFilter implements Filter {       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;       }       public void doFilter(ServletRequest request, ServletResponse response,               FilterChain chain) {           // 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;           // 记录日志           context.log("Filter已经截获到用户的请求的地址: " + hrequest.getServletPath());           try {               // Filter 只是链式处理，请求依然转发到目的地址。               chain.doFilter(request, response);           } catch (Exception e) {               e.printStackTrace();           }           long after = System.currentTimeMillis();           // 记录日志           context.log("过滤结束");           // 再次记录日志           context.log(" 请求被定位到" + ((HttpServletRequest) request).getRequestURI()                   + "所花的时间为: " + (after - before));       }   }