Filter链的使用及FilterConfig总结(代码实例)

(一)Filter链

说明：多个Filter程序，对用户请求的某一些URL进行拦截。多个Filter程序拦截同一个URL时，拦截顺序与Filter在web.xml配置文件的顺序有关。

实例演示

package com.TestFilterChain;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8"); 

        response.getWriter().print("---用户请求，我去做事---
");
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);
    }

}

package com.TestFilterChain;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class MyFilter01 implements Filter {

    public void destroy() {

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        response.setContentType("text/html;charset=utf-8"); 
        //1.如果请求URL与配置过滤器的URL相同，执行 doFilter()方法
        response.getWriter().print("1.首先MyFilter01拦截用户请求的MyServlet
");
        //2.放行
        chain.doFilter(request, response);
        response.getWriter().print("4.MyFilter01-----后响应
");
    }


    public void init(FilterConfig fConfig) throws ServletException {

    }

}

package com.TestFilterChain;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class MyFilter02 implements Filter {

    public void destroy() {

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        response.setContentType("text/html;charset=utf-8"); 
        //1.如果请求URL与配置过滤器的URL相同，执行 doFilter()方法
        response.getWriter().print("2.其次MyFilter02拦截用户请求的MyServlet
");
        //2.放行
        chain.doFilter(request, response);
        //3.放行后响应
        response.getWriter().print("3.MyFilter02-----先响应
");
    }


    public void init(FilterConfig fConfig) throws ServletException {

    }

}

  Project01
  
    index.html
  
  
    
    MyServlet
    MyServlet
    com.TestFilterChain.MyServlet
  
  
    MyServlet
    /MyServlet
  
  
    MyFilter01
    MyFilter01
    com.TestFilterChain.MyFilter01
  
  
    MyFilter01
    /MyServlet
  
  
    MyFilter02
    MyFilter02
    com.TestFilterChain.MyFilter02
  
  
    MyFilter02
    /MyServlet
  

输出：

(二)FilterConfig接口的使用

FilterConfig的方法：https://docs.oracle.com/javaee/6/api/javax/servlet/FilterConfig.html

FilterConfig对象获取web.xml文件的参数

实例演示：

package com.TestFilterChain;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8"); 
        response.getWriter().print("---用户请求我去做事--- ");
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);
    }

}

package com.TestFilterChain;
import java.io.*;
import javax.servlet.*;
public class MyFilter01 implements Filter {
    private String name;
    FilterConfig fc;
    public void init(FilterConfig fConfig) throws ServletException {
        //1.获取FilterConfig对象
        this.fc = fConfig;
    }
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        //2.输出参数信息

        name=fc.getInitParameter("name");
        response.getWriter().println("My name is  "+name+"
");
        chain.doFilter(request, response);
    }
    public void destroy() {
    }
}

  Project01
  
    
  
  
    MyFilter01
    MyFilter01
    com.TestFilterChain.MyFilter01
    
      name
      kaina
    
  
  
    MyFilter01
    /MyServlet
  
  
    
    MyServlet
    MyServlet
    com.TestFilterChain.MyServlet
  
  
    MyServlet
    /MyServlet
  

输出：