SpringBoot学习笔记：过滤器监听器拦截器

Posted 2022-11-21 听风者-better

本文介绍springboot中使用过滤器、监听器、拦截器

过滤器

过滤器，就是用来过滤web请求的
1）过滤器可以过滤所有的web 请求，包括静态页面
2）过滤器依赖于Servlet，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

监听器

监听器实际上是一个特殊的servlet。他的作用就是监听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、访问量等

拦截器

1）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，依赖于Spring

具体代码实现：

一.过滤器

1.使用配置类的方式

//定义过滤器
@Slf4j
public class MyFilter implements Filter 

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
        log.info("MyFilter过滤器开始执行");
        filterChain.doFilter(servletRequest, servletResponse);
        log.info("MyFilter过滤器结束执行");
    

    @Override
    public void destroy() 
        log.info("MyFilter过滤器销毁");
    


//过滤器配置
@Configuration
public class FilterConfig 

    @Bean
    public FilterRegistrationBean registrationBean() 
        FilterRegistrationBean bean = new FilterRegistrationBean();
        bean.setFilter(new MyFilter());
        bean.addUrlPatterns("/*");
        bean.setName("myFilter");
        bean.setOrder(1);//设置过滤的优先级
        return bean;
    

2.使用注解的方式

//定义过滤器
@Slf4j
@WebFilter(urlPatterns = "/test/*",filterName = "myFilter")
public class MyFilter implements Filter 

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
        log.info("MyFilter过滤器开始执行");
        filterChain.doFilter(servletRequest, servletResponse);
        log.info("MyFilter过滤器结束执行");
    

    @Override
    public void destroy() 
        log.info("MyFilter过滤器销毁");
    


//启动类
@SpringBootApplication
@ServletComponentScan("com.twy.springbootfilter.filter")
public class SpringbootFilterApplication 

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

二、监听器

实现一个简单的用户在线人数demo
1.使用配置类的方式

//定义监听器
@Slf4j
public class MyListener implements HttpSessionListener 

    private int count = 0;

    @Override
    public void sessionCreated(HttpSessionEvent se) 
        count++;
        log.info("用户上线了");
        se.getSession().getServletContext().setAttribute("count", count);
    

    @Override
    public void sessionDestroyed(HttpSessionEvent se) 
        count--;
        log.info("用户下线了");
        se.getSession().getServletContext().setAttribute("count", count);
    


//配置类
@Configuration
public class ListenerConfig 

    @Bean
    public ServletListenerRegistrationBean ServletListenerRegistrationBean()
        ServletListenerRegistrationBean<EventListener> registrationBean = new ServletListenerRegistrationBean<>();
        registrationBean.setListener(new MyListener());
        return registrationBean;
    


//控制层
@RestController
public class HelloController 

    @GetMapping("/count")
    public String count(HttpServletRequest request) 
        return "在线人数：" + request.getSession().getServletContext().getAttribute("count");
    

    @RequestMapping("/logOut")
    public String logOut(HttpServletRequest request) 
        request.getSession().invalidate();
        return "注销成功";
    

打开两个浏览器分别请求127.0.0.1:8080/count，请求创建了session，执行了监听器里sessionCreated方法，结果如下

请求127.0.0.1:8080/logOut注销了session，执行了监听器里sessionDestroyed方法，结果如下

2.使用注解的方式
和过滤器一样，添加@WebListener，@ServletComponentScan即可

三、拦截器

//定义拦截器
@Slf4j
public class MyInterceptor implements HandlerInterceptor 

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception 
        log.info("preHandle方法执行");
        return true;
    

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception 
        log.info("postHandle方法执行");
    

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception 
        log.info("afterCompletion方法执行");
    


//添加拦截配置
@Configuration
public class InterceptorConfig implements WebMvcConfigurer 
    @Override
    public void addInterceptors(InterceptorRegistry registry) 
        registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**");
    

需要注意的是preHandle()方法只有返回true，方法才会执行