springBoot的过滤器，监听器，拦截器

概述

　　在开发中，我们经常要考虑一些问题，对敏感词进行过滤，用户是否已经登录，是否需要对他的请求进行拦截，或者领导问现在在线人数有多少人？我们如何实现这些功能哪

 @WebFilter

package com.xmlxy.firstspringbootproject;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter(filterName = "customFilter",urlPatterns = "/*")
public class CustomFilter implements Filter {

    private static final Logger log = LoggerFactory.getLogger(CustomFilter.class);

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("===========拦截器初始化==========");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        log.info("doFilter请求处理");
    }

    @Override
    public void destroy() {
        log.info("fifter销毁");
    }
}

在application类中添加@ServletComponentScan注解

package com;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.context.annotation.PropertySource;

@SpringBootApplication
@ServletComponentScan
@PropertySource(value = "classpath:jdbc.properties",encoding = "utf-8")
public class FirstSpringbootProjectApplication {

    public static void main(String[] args) {
        SpringApplication.run(FirstSpringbootProjectApplication.class, args);
    }

}

运行结果

（笔误，应该是过滤器初始化）过滤器已经生效，但若有多个过滤器，无法指定执行顺序，我们可以通过Java类的名称，从A-L，按顺序执行。但这种方式毕竟不大靠谱，所以，有第二种写法，它提供setOrder函数，为filter设置排序值。

package com.xmlxy.service;

import com.xmlxy.firstspringbootproject.CustomFilter;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class WebFilterConfig
{
    @Bean
    public FilterRegistrationBean someFilterRegistration1()
    {
        FilterRegistrationBean registration = new FilterRegistrationBean<>();
        System.out.println("我执行了。。。。。。。");
        registration.setFilter(new CustomFilter());
        registration.addUrlPatterns("/*");

　　　　 registration.setOrder(1);

　　　　 return registration; } }

我们尝试写个demo，验证一下过滤器是否执行。

用户登录对象

User.java

package com.xmlxy.bean;

import lombok.Data;
import org.springframework.stereotype.Component;

@Data
@Component
public class User {
    private String user;
    private String pwd;
}

登录控制

LoginController.java

package com.xmlxy.firstspringbootproject;

import com.xmlxy.bean.User;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

@RestController
public class LoginController {

    @RequestMapping(value = "login",method = RequestMethod.GET)
    public String login(HttpServletRequest request)
    {
        String user = request.getParameter("user");
        String pwd = request.getParameter("pwd");
        HttpSession session = request.getSession();
        if ("admin".equals(user) && "admin".equals(pwd))
        {
            User user1 = new User();
            user1.setUser(user);
            user1.setPwd(pwd);
            session.setAttribute("user",user1);
            return "登录成功";
        }
        return "密码错误，登录失败";
    }

　　@RequestMapping(value = "test",method = RequestMethod.GET)
　　public String test()
　　{
    　　return "test接口";
　　}

}

过滤器

CustomFilter.java

package com.xmlxy.firstspringbootproject;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
//@WebFilter(filterName = "customFilter",urlPatterns = "/*")
public class CustomFilter implements Filter {

    private static final Logger log = LoggerFactory.getLogger(CustomFilter.class);

    String includes[] = {"/login","register"};

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("===========过滤器初始化==========");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
    {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        HttpSession session = request.getSession(false);
        String uri = request.getRequestURI();
        boolean flag = isNeedFilter(uri);
        if (!flag)
        {
            filterChain.doFilter(servletRequest,servletResponse);
            System.err.printf("登录成功");
        }else {
            if (session != null && session.getAttribute("user") != null)
            {
                filterChain.doFilter(servletRequest,servletResponse);
            }else {
                System.err.printf("暂时未登录");
            }
        }

        log.info("doFilter请求处理");
    }
    public boolean isNeedFilter(String uri)
    {
        for (String include:includes)
        {
            if (include.equals(uri))
            {
                return false;
            }
        }
        return true;
    }
    @Override
    public void destroy() {
        log.info("fifter销毁");
    }
}

过滤器配置

WebFilterConfig

package com.xmlxy.service;

import com.xmlxy.firstspringbootproject.CustomFilter;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class WebFilterConfig
{
    @Bean
    public FilterRegistrationBean someFilterRegistration1()
    {
        FilterRegistrationBean registration = new FilterRegistrationBean<>();
        System.out.println("我执行了。。。。。。。");
        registration.setFilter(new CustomFilter());
        registration.addUrlPatterns("/*");
        return registration;
    }
}

 运行测试。。访问 127.0.0.1/test  控制台

访问  http://127.0.0.1:8080/login?user=admin&pwd=admin，可以看到登录成功

在次访问 127.0.0.1/test 页面显示

所以，我们的过滤器成功过滤未登录的用户

监听器

正在你为自己会了过滤用户自鸣得意时，你的组长过来了，小明，你看下我们平台的在线用户有多少人。如果不知道监听器童鞋，是否会在登录接口处每次登录成功都+1，然而这种统计结果是不准确的，因为用户如果反复登录退出，那这个在值就远远大于实际值，最后就面临着，加班在加班的悲惨下场。

CustomLister.java

package com.xmlxy.firstspringbootproject;


import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

@WebFilter
public class CustomLister implements HttpSessionListener
{
    public static int online = 0;

    @Override
    public void sessionCreated(HttpSessionEvent sessionEvent)
    {
        System.out.println("创建session,统计在线人数");
        online ++;
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent sessionEvent)
    {
        System.out.println("session已经销毁");
    }
}

配置监听器配置,在刚才的WebFilterConfig.java添加

@Bean
    public ServletListenerRegistrationBean listenerRegistrationBean()
    {
        ServletListenerRegistrationBean srb = new ServletListenerRegistrationBean();
        srb.setListener(new CustomLister());
        System.out.println("");
        return srb;
    }

添加一个访问在线人数的接口

@RequestMapping(value = "onLinePerson",method = RequestMethod.GET)
    public String onLinePerson()
    {
        StringBuffer stringBuffer = new StringBuffer("");
        stringBuffer.append(" 在线人数 ");
        stringBuffer.append(CustomLister.online);
        stringBuffer.append(" 个人 ");
        return stringBuffer.toString();
    }

访问127.0.0.1/onLinePerson,发现被拦截器拦截了，我们先登录。在查看接口

换个浏览器，调用下login接口，在查看

拦截器

拦截器，个人理解，在web上有些像是过滤器的补充，它能更精确的控制拦截哪些函数或者字段，在拦截之前或之后做一些操作。我们现在做一个敏感词的拦截，其实这个操作放在过滤器操作也是可以的，但lz因为刚才把拦截用户的操作放在过滤器了，在大规模更改，lz觉得没必要，因为都是大同小异。

CustomInterceptor.java

package com.xmlxy.firstspringbootproject;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.PrintWriter;

public class CustomInterceptor implements HandlerInterceptor
{
    private static final Logger log = LoggerFactory.getLogger(CustomInterceptor.class);
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,Object handler) throws Exception {
        log.info("=======拦截器被调用=====");
        String url = request.getRequestURI();
        if (url != null && url.indexOf("seqing") != -1)
        {
            PrintWriter printWriter = response.getWriter();
            printWriter.write("ming gan ci");
            return false;
        }
        log.info("返回false 则中断请求");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
    {
        log.info("请求后调用");
    }

    @Override
    public void afterCompletion(HttpServletRequest request,HttpServletResponse response,Object handler,Exception e)
    {
        log.info("视图渲染完回调");
    }
}

配置拦截

package com.xmlxy.service;

import com.xmlxy.firstspringbootproject.CustomFilter;
import com.xmlxy.firstspringbootproject.CustomInterceptor;
import com.xmlxy.firstspringbootproject.CustomLister;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebFilterConfig implements WebMvcConfigurer
{
    @Bean
    public FilterRegistrationBean someFilterRegistration1()
    {
        FilterRegistrationBean registration = new FilterRegistrationBean<>();
        System.out.println("我执行了。。。。。。。");
        registration.setFilter(new CustomFilter());
        registration.addUrlPatterns("/*");
        return registration;
    }

    @Bean
    public ServletListenerRegistrationBean listenerRegistrationBean()
    {
        ServletListenerRegistrationBean srb = new ServletListenerRegistrationBean();
        srb.setListener(new CustomLister());
        return srb;
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry)
    {
        /*拦截规则*/
        registry.addInterceptor(new CustomInterceptor()).addPathPatterns("/*");
    }

}

现在测试访问127.0.0.1/seqing，被过滤，要求先登录。我们调用登录接口后，再次调用，发现被拦截了

看下日志调用，可以发现，拦截器是在访问接口前被调用的

过滤器，拦截器区别

这里主要说下拦截器和过滤器的区别和使用场景，通过demo可以发现，它们都能实现权限的检查，日志记录这些功能，主要说下它们的区别

1. 过滤器和拦截器触发的时机是不同的，在进入servlet之前，过滤器就进行预处理了。而拦截器是在调用Controller之前才触发执行，过滤器的范围较广，对所有的请求都起作用，而拦截起只 对action起作用

　　2.拦截器可以获取IOC容器的各个bean，而过滤器就不行。因为拦截器是spring提供管理的，也因此拦截器可以使用spring的任何资源。

　　3.拦截器是利用Java反射机制实现，过滤器是函数的回调。因此实现方式是不同的。

三者使用场景

　　监听器：常用统计在线用户，统计网站的访问量，记录用户的访问路径

　　过滤器：过滤敏感词，权限访问控制

　　拦截器：权限验证，判断用户是否登录等