springboot中的过滤器、拦截器、监听器区别及具体实现

一 、过滤器：

顾名思义，过滤器，就是用来过滤web请求的，所以关注点是web请求，
1）过滤器可以过滤所有的web 请求，包括静态页面
2）过滤器基于servlet规定的，所以依赖于web容器，所以只能过滤web请求
一般用来过滤敏感词、URL级别的访问权限控制等

springboot中实现

1、注册类的方式

添加controller

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
@RequestMapping(value="/test")
public class HelloController {

    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    public String hello(){
        return "hello!";
    }
}

添加过滤器

import javax.servlet.*;
import java.io.IOException;

public class FilterDemoClass implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("==========过滤器初始化==========");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("==========过滤器开始执行==========");
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("==========过滤器结束执行==========");
    }

    @Override
    public void destroy() {
        System.out.println("==========过滤器销毁==========");
    }
}

对过滤器进行注册

import com.xyzh.filterdemo.filter.FilterDemoClass;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;

import java.util.ArrayList;
import java.util.List;

@SpringBootApplication
public class FilterDemoApplication {

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

    @Bean
    public FilterRegistrationBean filterRegistrationBean() {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();
        registrationBean.setFilter(new FilterDemoClass()); // 自己的filter

        List urlPatterns = new ArrayList<>();
        urlPatterns.add("/test/*");
        registrationBean.setUrlPatterns(urlPatterns);
        return registrationBean;
    }

}

2、注解的方式

在过滤器类的上面加上注解：

@WebFilter(filterName = "suFilter",urlPatterns = "/test/*")
@Configuration

可以去掉启动类中的 bean的部分。

二、拦截器：

1）可以认为拦截器只能拦截action请求，不拦截静态页面等，
2）拦截器基于反射机制实现，所以不依赖于web容器
3）拦截器可以获取action上下文的ModelAndView对象的值
用于处理action，比如处理日志等

通过实现HandlerInterceptor接口的 方式

1、添加拦截器

import lombok.extern.slf4j.Slf4j;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@Slf4j
@Component
public class MyInterceptor implements HandlerInterceptor {
    private final static Logger logger= LoggerFactory.getLogger(MyInterceptor.class);

    //预处理回调方法
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,Object handler)
            throws  Exception{

        System.out.println("拦截器开始拦截....");
        return false;
    }

    //处理逻辑，在controller后调用
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           ModelAndView modelAndView) throws Exception {
        System.out.println("拦截器工作中....");

    }
    //处理完成后处理逻辑
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
         System.out.println("拦截器已经结束....");
    }

}

2、配置拦截器

import com.xyzh.filterdemo.filter.MyInterceptor;
import org.springframework.beans.factory.annotation.Autowired;
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 MyInterceptorConfig implements WebMvcConfigurer {
    //这个方法是用来配置拦截器的
    @Autowired
    private MyInterceptor interceptor;
    @Override
    public void addInterceptors(InterceptorRegistry registry){

        registry.addInterceptor(interceptor).addPathPatterns("/**").excludePathPatterns("/login,/register");

    }
}

启动后看下控制台输出：

==========过滤器开始执行==========
拦截器开始拦截....
==========过滤器结束执行==========

三、监听器

监听器实际上是一个特殊的servlet。他的作用很单一，就是监听servletContext、HttpSession、ServeltRequest等对象的的创建或者销毁以及属性值发生改变的事件
一般用于统计在线人数、访问量、埋点（用户访问路径）等

1、创建监听器

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class MyListener implements ServletRequestListener {
    @Override
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {

        System.out.println("监听器销毁请求");
    }
    @Override
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {

        System.out.println("监听器初始化请求");
    }



}

2、在启动类上声明

@ServletComponentScan(basePackages = "com.hkjs.filterdemo.*")