Java Filter工作原理

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这里写图片描述

用户的请求可以理解为转化为两个方向
1. doFilter是一个viod方法.那么doFilter方法的前后都可以处理.
2.request 与 response一些参数的修改.
3.response.getWriter()输出流输出到用户浏览器端
4.Filter中一样可以对流进行获取,并增加输出.

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {        // TODO Auto-generated method stub        // place your code here        System.out.println("f1 start");        chain.doFilter(request, response);        System.out.println("f1 end");    }

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {        // TODO Auto-generated method stub        // place your code here        // pass the request along the filter chain        System.out.println("f2 start");        chain.doFilter(request, response);        //这里可以追加输出        System.out.println(response.getWriter().append("f2"));        System.out.println("f2 end");    }

/** * Servlet implementation class S1 */@WebServlet("/S1")public class S1 extends HttpServlet {    private static final long serialVersionUID = 1L;    /**     * @see HttpServlet#HttpServlet()     */    public S1() {        super();        // TODO Auto-generated constructor stub    }    /**     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)     */    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        System.out.println("s1 start");        response.getWriter().append("Served at: ").append(request.getContextPath());        System.out.println("s1 end");    }    /**     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)     */    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        doGet(request, response);    }}

最后访问url的输出.f1 startf2 starts1 starts1 endorg.apache.catalina.connector.CoyoteWriter@100433abf2 endf1 end

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