04_过滤器Filter_02_Filter解决中文乱码问题

 【过滤器解决中文乱码问题实例】

【工程截图】

 【web.xml】

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>FilterDemo01</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <filter>
    <filter-name>FilterTest01</filter-name>
    <filter-class>com.Higgin.web.filter.FilterTest01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>FilterTest01</filter-name>
    <url-pattern>/*</url-pattern> <!-- 过滤所有 -->
  </filter-mapping>
    
</web-app>

【servletTest01.java】

package com.Higgin.web.servlet;

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

/**
 * Servlet implementation class ServletTest01
 */
@WebServlet("/ServletTest01")
public class ServletTest01 extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public ServletTest01() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().write("中国 加油！China Come on!");   //将"中国 加油！China Come on!"显示在客户端界面上
    }

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

}

【情况一：未添加中文乱码过滤】

【FilterTest01.java】

package com.Higgin.web.filter;

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 FilterTest01 implements Filter{

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        
        System.out.println("I'm Filter!!!!");
        //直接放行
        chain.doFilter(request, response);//让目标资源执行，即：放行
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        
    }
    
    @Override
    public void destroy() {
        
    }
}

【运行结果】

浏览器端

控制台

【情况二：在Filter的都doFilter()方法中添加中文乱码过滤处理】

【FilterTest01.java】

package com.Higgin.web.filter;

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 FilterTest01 implements Filter{

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        
        System.out.println("I'm Filter!!!!");
        
        //对request和response进行一些预处理
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;character=UTF-8");
        
        chain.doFilter(request, response);//让目标资源执行，即：放行
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        
    }
    
    @Override
    public void destroy() {
        
    }
}

 【运行结果】

浏览器端

控制台

 

【三种典型应用概述】

1.可以在Filter中根据条件决定是否调用chain.doFilter(request,response)方法，即是否放行让目标资源执行。

2.在目标资源执行之前，可以对request/response做预处理，再让目标资源执行。（如：为request和reponse设置编码为utf-8，以解决中文乱码问题）

3.让目标资源执行之后，可以捕获目标资源的执行结果，从而实现一些特殊的功能。