过滤器的使用

过滤器的使用

Filter原理

使用Filter前后对比

package com.fakelogin.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 MyFilter implements Filter{

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub


        request.setCharacterEncoding("UTF-8");

        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");

        chain.doFilter(request, response);
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("--------Filter初始化-------");
    }

}

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="2.5"
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
        
  <welcome-file-list> 
    <welcome-file>  login.html </welcome-file>
    <welcome-file>  login.htm </welcome-file>
    <welcome-file>  login.jsp </welcome-file>
  </welcome-file-list>
 
   <filter>
     <filter-name>MyFilter</filter-name>
     <filter-class>com.fakelogin.filter.MyFilter</filter-class>
   </filter>
   
   <filter-mapping>
        <filter-name>MyFilter</filter-name>
        <!-- 拦截所有的请求 -->
        <url-pattern>/*</url-pattern>
   </filter-mapping>
   
  <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.fakelogin.servlet.LoginServlet</servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/servlet/LoginServlet</url-pattern>
  </servlet-mapping>
  


  
</web-app>

遇到的一点问题

在写好Filter类并配置好.xml后，

提交表单却不能解决用户名乱码。

经过几次尝试后依然是不起作用，

突然发现MyFilter里有几行输出，

将其删除后程序竟成功跑起来了。

百度云

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参考链接

http://www.codebelief.com/article/2017/09/java-web-understand-servlet-filter-listener-via-three-pictures/