Java拦截器、过滤器和监听器的区别与作用详解

import org.springframework.web.servlet.HandlerInterceptor;

public class MyInterceptor implements HandlerInterceptor {
    // 在请求处理之前执行
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        System.out.println("请求处理前执行");
        return true; // 返回 false 可以阻止请求继续处理
    }

    // 在请求处理之后执行
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) {
        System.out.println("请求处理后执行");
    }

    // 在整个请求完成之后执行
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        System.out.println("请求处理完成执行");
    }
}

<mvc:interceptors>
    <bean class="com.example.MyInterceptor"/>
</mvc:interceptors>

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

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

    // 拦截请求和响应
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
        System.out.println("请求前处理");
        chain.doFilter(request, response); // 放行请求
        System.out.println("响应后处理");
    }

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

<filter>
    <filter-name>myFilter</filter-name>
    <filter-class>com.example.MyFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>myFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

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

public class MyListener implements HttpSessionListener {
    private static int onlineCount = 0;

    // 会话创建时触发
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        onlineCount++;
        System.out.println("会话创建，当前在线人数：" + onlineCount);
    }

    // 会话销毁时触发
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        onlineCount--;
        System.out.println("会话销毁，当前在线人数：" + onlineCount);
    }
}

<listener>
    <listener-class>com.example.MyListener</listener-class>
</listener>