springboot实现过滤器

一 过滤器介绍

1.1 过滤器概念

过滤器，即filter，它是javaWeb三大组件之一（Servlet程序、Listener监听器、Filter过滤器）

作用：既可以对请求进行拦截，也可以对响应进行处理。常用于做权限检查，记录日志操作、拦截过滤请求、对请求字符设置编码等。

1.2 过滤器生命周期

SpringBoot定义一个过滤器很简单，只需要实现Filter类，然后重写它的3个方法即可。

• init方法：程序启动调用Filter的init()方法，永远只调用一次；在容器中创建当前过滤器的时候自动调用这个方法。
• destory方法：程序停止调用Filter的destroy()方法，永远只调用一次；在容器中销毁当前过滤器的时候自动调用这个方法。
• doFilter方法：每次的访问请求如果符合拦截条件都会调用doFilter()方法，程序第一次运行，会在servlet调用init()方法以后调用doFilter()方法；不管第几次请求，都是在调用servlet的doGet(),doPost()方法之前调用。这个方法有3个参数，分别是ServletRequest、ServletResponse和FilterChain，可以从这些参数中获取HttpServletReguest和HttpServletResponse对象进行相应的处理操作。

二 SpringBoot中过滤器的两种实现方式

2.1 注解方式实现过滤器

首先需要在启动类加 @ServletComponentScan 注解，启动类如下

importorg.mybatis.spring.annotation.MapperScan;importorg.springframework.boot.SpringApplication;importorg.springframework.boot.autoconfigure.SpringBootApplication;importorg.springframework.boot.web.servlet.ServletComponentScan;@SpringBootApplication@MapperScan("com.ts.myt.dao")@ServletComponentScan// 过滤器publicclassMytApplication{publicstaticvoidmain(String[] args){SpringApplication.run(MytApplication.class, args);}}

编写过滤器，实现Filter接口

importcom.alibaba.fastjson.JSONObject;importorg.slf4j.Logger;importorg.slf4j.LoggerFactory;importjavax.servlet.*;importjavax.servlet.annotation.WebFilter;importjavax.servlet.http.HttpServletRequest;importjava.io.IOException;importjava.io.PrintWriter;/**
 * @Author:sgw
 * @Date:2023/9/15
 * @Description: 使用注解方式实现过滤器（@WebFilter）
 */@WebFilter(urlPatterns ="/user/*", filterName ="filter1")publicclassMyFilterimplementsFilter{privatestaticfinalLogger logger =LoggerFactory.getLogger(MyFilter.class);@Overridepublicvoidinit(FilterConfig filterConfig)throwsServletException{//        Filter.super.init(filterConfig);
        logger.info("MyFilterInit1");}@OverridepublicvoiddoFilter(ServletRequest servletRequest,ServletResponse servletResponse,FilterChain filterChain)throwsIOException,ServletException,IOException{
        logger.info("doFilter");HttpServletRequest request =(HttpServletRequest) servletRequest;String token = request.getHeader("token");
        logger.info("token值：{}", token);if(token !=null){//该方法执行后直接运行至下一个过滤器
            filterChain.doFilter(servletRequest, servletResponse);}else{
            servletResponse.setCharacterEncoding("UTF-8");
            servletResponse.setContentType("application/json; charset=utf-8");PrintWriter out = servletResponse.getWriter();JSONObject res =newJSONObject();
            res.put("msg","错误");
            res.put("success","false");
            out.append(res.toString());}}@Overridepublicvoiddestroy(){//        Filter.super.destroy();
        logger.info("destroy");}}

上边对请求头header做了过滤，即请求头里必须含有key为token的值，才能继续访问具体接口，否则该请求就终止访问接口了

2.2 非注解方式实现过滤器（直接注入到spring中）

定义过滤器，同样实现Filter接口

importcom.alibaba.fastjson.JSONObject;importorg.slf4j.Logger;importorg.slf4j.LoggerFactory;importjavax.servlet.*;importjavax.servlet.http.HttpServletRequest;importjava.io.IOException;importjava.io.PrintWriter;/**
 * @Author:sgw
 * @Date:2023/9/15
 * @Description: 过滤器实现方式二：使用非注解方式实现过滤器（直接注入到spring中）
 */publicclassMyFilter2implementsFilter{privatestaticfinalLogger logger =LoggerFactory.getLogger(MyFilter2.class);@Overridepublicvoidinit(FilterConfig filterConfig)throwsServletException{
        logger.info("MyFilterInit2");}@OverridepublicvoiddoFilter(ServletRequest servletRequest,ServletResponse servletResponse,FilterChain filterChain)throwsIOException,ServletException,IOException{System.out.println("doFilter");HttpServletRequest request =(HttpServletRequest) servletRequest;String token = request.getHeader("token");System.out.println(token);//该方法执行后直接运行至下一个过滤器if(token!=null){
            filterChain.doFilter(servletRequest, servletResponse);}else{
            servletResponse.setCharacterEncoding("UTF-8");
            servletResponse.setContentType("application/json; charset=utf-8");PrintWriter out = servletResponse.getWriter();JSONObject res =newJSONObject();
            res.put("msg","错误");
            res.put("success","false");
            out.append(res.toString());}}@Overridepublicvoiddestroy(){System.out.println("destroy");}}

编写过滤器配置类

importcom.ts.myt.filter.MyFilter2;importorg.springframework.boot.web.servlet.FilterRegistrationBean;importorg.springframework.context.annotation.Bean;importorg.springframework.context.annotation.Configuration;/**
 * @Author:sgw
 * @Date:2023/9/15
 * @Description: 方式二的过滤器配置文件
 */@ConfigurationpublicclassMyFilter2Config{// Filter代码类@BeanpublicMyFilter2myFilter2(){returnnewMyFilter2();}@BeanpublicFilterRegistrationBeangetFilterRegistrationBean(MyFilter2 myFilter2){FilterRegistrationBean filterRegistrationBean =newFilterRegistrationBean();
        filterRegistrationBean.setFilter(myFilter2);
        filterRegistrationBean.setOrder(2);
        filterRegistrationBean.addUrlPatterns("/user/*");
        filterRegistrationBean.setName("tokenFilter2");return filterRegistrationBean;}}

效果与方式一一样。