过滤器 拦截器 监听器

过滤器

实现

实现Filter类,然后重写它的3个方法:

• init 方法 : 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 : 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 : 这个方法有3个参数,分别是 ServletRequest,ServletResponse和FilterChain.可以在参数中获取 HttpServletRequest和 HttpServletResponse对象进行相应的处理操作.

在springboot项目中使用filter ,自定义MyFilter类:

import lombok.extern.slf4j.Slf4j;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

@Slf4j
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("init 方法被调用");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        log.info("doFilter 方法被调用");
        HttpServletRequest httpServletRequest = (HttpServletRequest)request;
        String s = httpServletRequest.getRequestURL().toString();
        log.info("url : "+s);
        filterChain.doFilter(request,response);
    }

    @Override
    public void destroy() {
        log.info("destroy 方法被调用");
    }
}

然后在添加到filterChain中

@Configuration
public class WebAppConfigurer implements WebMvcConfigurer {
    @Bean
    public FilterRegistrationBean filterRegist(){
        FilterRegistrationBean frBean = new FilterRegistrationBean();
        frBean.setFilter(new MyFilter());
        frBean.addUrlPatterns("/*");
        return  frBean;
    }
}

init 方法在项目启动的时候会调用

doFilter 方法在每次请求的时候会调用

过滤器也可以配合@WebFilter和@ServletComponentScan使用,详情参见@WebFilter

拦截器

java中拦截器是动态拦截action调用的对象,然后提供可以在action执行前后增加一些操作,也可以在action执行前停止操作.拦截器可以做和过滤器同样的操作

springBoot 中使用拦截器

@Slf4j
@Component
public class LoginHandlerInterceptor implements HandlerInterceptor {

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

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

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

@Configuration
public class WebAppConfigurer implements WebMvcConfigurer {
    @Bean
    public LoginHandlerInterceptor loginHandlerInterceptor(){ return new LoginHandlerInterceptor();}
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        List<String> excludes = new ArrayList<>();
        excludes.add("/api/**");
        excludes.add("/js/**");
        excludes.add("/css/**");
        excludes.add("/img/**");
        excludes.add("/lib/**");
        excludes.add("/fonts/**");
  registry.addInterceptor(loginHandlerInterceptor()).addPathPatterns("/**").excludePathPatterns(excludes);
    }
}

监听器

监听器通常用于监听Web应用中对象的创建,销毁等动作的发生,同时对监听的情况作出相应的处理,最常用于统计网站的在线人数,访问量等信息

• ServletContextListener : 用来监听ServletContext属性的操作,比如新增修改删除
• HttpSessionListener : 用来监听Web应用中的Session对象,常用于统计在线情况
• ServletRequestListener : 用来监听Request对象的属性操作

使用监听器需要在类中实现对应功能的监听器对象,例如实现 HttpSessionListener 类

import lombok.extern.slf4j.Slf4j;

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

@Slf4j
public class MyHttpSessionListener implements HttpSessionListener {

    private static int online = 0;

    @Override
    public void sessionCreated(HttpSessionEvent event){
        log.info("sessionCreated 方法");
        online++;
        log.info("online : "+online);
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        log.info("sessionDestroyed 方法");
        online--;
        log.info("online : "+online);
    }
}

@Configuration
public class WebAppConfigurer implements WebMvcConfigurer {
    @Bean
    public ServletListenerRegistrationBean listenerRegistrationBean(){
        ServletListenerRegistrationBean srb = new ServletListenerRegistrationBean();
        srb.setListener(new MyHttpSessionListener());
        return srb;
    }
}

监听器可以在MyHttpSessionListener类上添加注解@WebListener,并且在启动类上加上@ServletComponentScan这样就不用在WebAppConfigurer配置类中配置了

import javax.servlet.annotation.WebListener;

@WebListener
@Slf4j
public class MyHttpSessionListener implements HttpSessionListener {
    private static int online = 0;
      @Override
    public void sessionCreated(HttpSessionEvent event){
        log.info("sessionCreated 方法");
        online++;
        log.info("online : "+online);
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        log.info("sessionDestroyed 方法");
        online--;
        log.info("online : "+online);
    }
}

本篇文章由一文多发平台ArtiPub自动发布