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Filter:过滤器

概念：当访问服务器的资源是，过滤器可以将请求拦截下来，完成一些特殊的功能

快速入门：

步骤：

定义一个类，实现接口Filter
复写方法
配置拦截路径

package com.data.web.filter; import javax.servlet.*; import javax.servlet.annotation.WebFilter; import java.io.IOException; @WebFilter("/*")//访问所有资源之前，都会执行该过滤器 public class FilterDemo1 implements Filter{ @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { System.out.println("Filter被执行了");//当访问资源是，过滤器就会被执行 //放行 filterChain.doFilter(servletRequest,servletResponse);//放行之后才可以访问资源 } @Override public void destroy() { } } package com.data.web.filter; import javax.servlet.*; import javax.servlet.annotation.WebFilter; import java.io.IOException; @WebFilter("/*")//访问所有资源之前，都会执行该过滤器 public class FilterDemo1 implements Filter{ @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { System.out.println("Filter被执行了");//当访问资源是，过滤器就会被执行 //放行 filterChain.doFilter(servletRequest,servletResponse);//放行之后才可以访问资源 } @Override public void destroy() { } }

过滤器的执行流程

<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>$Title$</title> </head> <body> <% System.out.println("执行index.jsp....."); %> </body> </html>package com.data.web.filter; import javax.servlet.*; import javax.servlet.annotation.WebFilter; import java.io.IOException; @WebFilter("/*") public class FilterDemo2 implements Filter{ @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { //放行前可以对请求数据增强 System.out.println("filterDemo2执行了...."); filterChain.doFilter(servletRequest,servletResponse); //放行后可以对响应的数据增强 System.out.println("filterDemo2回来了...."); } @Override public void destroy() { } } package com.data.web.filter; import javax.servlet.*; import javax.servlet.annotation.WebFilter; import java.io.IOException; @WebFilter("/*") public class FilterDemo2 implements Filter{ @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { //放行前可以对请求数据增强 System.out.println("filterDemo2执行了...."); filterChain.doFilter(servletRequest,servletResponse); //放行后可以对响应的数据增强 System.out.println("filterDemo2回来了...."); } @Override public void destroy() { } }filterDemo2执行了.... 执行index.jsp..... filterDemo2回来了.... filterDemo2执行了.... 执行index.jsp..... filterDemo2回来了....