Servlet 监听器

Posted 2021-01-19 houhou87

Servlet监听器

所有事件都继承自 java.util.Event

分成三类：application范围、session范围和request范围

• 监听器接口和注册

  • javax.servlet.ServletContextListener: 响应 ServletContext生命周期事件，Context创建之后，关闭之前会被调用
  • javax.servlet.ServletContextAttributeListener: 响应Context范围的属性 增删替换
  • javax.servlet.http.HttpSessionListener: 响应session创建 超时 失效事件
  • javax.servlet.http.HttpSessionAttributeListener:
  • javax.servlet.http.HttpSessionActivationListener: 响应session失效 激活事件
  • javax.servlet.http.HttpSessionBindingListener: 响应HttpSession中有 添加 删除 值时
  • javax.servlet.ServletRequestListener: 响应ServletRequest的创建or删除
  • javax.servlet.ServletRequestAttributeListener:
  • javax.servlet.AsyncListener: 异步操作监听器

• Servlet3.0 - 3.1 两种方法实现

  • @WebListener
    public class ListenerClass implements ListenerInterface{}

  • <listener>
        <listener-class>fully-qualified listener class </istener-class>
    </listener>

• javax.servlet.ServletContextListener

  • public interface ServletContextListener extends EventListener {
        void contextInitialized(ServletContextEvent var1);
    
        void contextDestroyed(ServletContextEvent var1);
    }
    
    //监听器方法入参类型
    public class ServletContextEvent extends EventObject {
        private static final long serialVersionUID = 1L;
    
        public ServletContextEvent(ServletContext source) {
            super(source);
        }
    
        public ServletContext ServletContextEvent() {
            return (ServletContext)super.getSource();
        }
    }

  • 通过入参ServletContextEvent中的ServletContextEvent()可以获取应用上下文获取数据

  • 对ServletContext创建和销毁做出反应

• javax.servlet.ServletContextAttributeListener

  • public interface ServletContextAttributeListener extends EventListener {
        void attributeAdded(ServletContextAttributeEvent var1);
    
        void attributeRemoved(ServletContextAttributeEvent var1);
    
        void attributeReplaced(ServletContextAttributeEvent var1);
    }
    
    
    
    //监听器方法入参类型
    public class ServletContextAttributeEvent extends ServletContextEvent {
        private static final long serialVersionUID = 1L;
        private final String name;
        private final Object value;
    
        public ServletContextAttributeEvent(ServletContext source, String name, Object value) {
            super(source);
            this.name = name;
            this.value = value;
        }
    
        public String getName() {
            return this.name;
        }
    
        public Object getValue() {
            return this.value;
        }
    }
    

• javax.servlet.http.HttpSessionListener

  • public interface HttpSessionListener extends EventListener {
        void sessionCreated(HttpSessionEvent var1);
    
        void sessionDestroyed(HttpSessionEvent var1);
    }
    
    
    //监听器方法入参类型
    public class HttpSessionEvent extends EventObject {
        private static final long serialVersionUID = 1L;
    
        public HttpSessionEvent(HttpSession source) {
            super(source);
        }
    
        public HttpSession getSession() {
            return (HttpSession)super.getSource();
        }
    }

• javax.servlet.http.HttpSessionActivationListener

  • public interface HttpSessionAttributeListener extends EventListener {
        void attributeAdded(HttpSessionBindingEvent var1);
    
        void attributeRemoved(HttpSessionBindingEvent var1);
    
        void attributeReplaced(HttpSessionBindingEvent var1);
    }
    
    
    
    //监听器方法入参类型
    public class HttpSessionBindingEvent extends HttpSessionEvent {
        private static final long serialVersionUID = 1L;
        private final String name;
        private final Object value;
    
        public HttpSessionBindingEvent(HttpSession session, String name) {
            super(session);
            this.name = name;
            this.value = null;
        }
    
        public HttpSessionBindingEvent(HttpSession session, String name, Object value) {
            super(session);
            this.name = name;
            this.value = value;
        }
    
        public HttpSession getSession() {
            return super.getSession();
        }
    
        public String getName() {
            return this.name;
        }
    
        public Object getValue() {
            return this.value;
        }
    }

  • HttpSessionBindingEvent extends HttpSessionEvent 所以 在HttpSessionBindingEvent 也能够拿到HttpSession对象

• javax.servlet.http.HttpSessionActivationListener
  在分布式环境下，会用多个容器来进行负载均衡，有可能需要将session保存起来，在容器之间传递，ex一个容器内存不足，会将很少用到的对象转存刀其他容器上，这时候就会通知HttpSessionActivationListener

  • public interface HttpSessionActivationListener extends EventListener {
        //钝化
        void sessionWillPassivate(HttpSessionEvent var1);
        //活化
        void sessionDidActivate(HttpSessionEvent var1); 
    }

• javax.servlet.http.HttpSessionBindingListener

  • public interface HttpSessionBindingListener extends EventListener {
        void valueBound(HttpSessionBindingEvent var1);
    
        void valueUnbound(HttpSessionBindingEvent var1);
    }

• javax.servlet.ServletRequestListener

  • public interface ServletRequestListener extends EventListener {
        void requestDestroyed(ServletRequestEvent var1);
    
        void requestInitialized(ServletRequestEvent var1);
    }
    
    
    
    //监听器方法入参类型
    public class ServletRequestEvent extends EventObject {
        private static final long serialVersionUID = 1L;
        private final transient ServletRequest request;
    
        public ServletRequestEvent(ServletContext sc, ServletRequest request) {
            super(sc);
            this.request = request;
        }
    
        public ServletRequest getServletRequest() {
            return this.request;
        }
    
        public ServletContext getServletContext() {
            return (ServletContext)super.getSource();
        }
    }

• javax.servlet.ServletRequestAttributeListener

  • public interface ServletRequestAttributeListener extends EventListener {
        void attributeAdded(ServletRequestAttributeEvent var1);
    
        void attributeRemoved(ServletRequestAttributeEvent var1);
    
        void attributeReplaced(ServletRequestAttributeEvent var1);
    }