javaWeb监听器Listener（一）

Listener监听器

一、背景描述

javaweb中的监听器，是用于监听javaweb对象

例如：HttpServletRequest、HttpSession、ServletContext
监听他们的创建和销毁、属性变化、session绑定javaBean

二、javaWeb常见的监听器

1、监听域对象的创建和销毁

（1）如果要监听ServletContext创建和销毁 ---- 需要自定义实现类，来实现监听接口 ServletContextListener

package javax.servlet;

import java.util.EventListener;

public interface ServletContextListener extends EventListener {
    default void contextInitialized(ServletContextEvent sce) {
    }

    default void contextDestroyed(ServletContextEvent sce) {
    }
}
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（2）如果要监听HttpSession创建和销毁 ---- 需要自定义实现类，来实现监听接口 HttpSessionListener

package javax.servlet.http;

import java.util.EventListener;

public interface HttpSessionListener extends EventListener {
    default void sessionCreated(HttpSessionEvent se) {
    }

    default void sessionDestroyed(HttpSessionEvent se) {
    }
}

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（3）如果要监听HttpServletRequest创建和销毁 ---- 需要自定义实现类，来实现监听接口 ServletRequestListener

package javax.servlet;

import java.util.EventListener;

public interface ServletRequestListener extends EventListener {
    default void requestDestroyed(ServletRequestEvent sre) {
    }

    default void requestInitialized(ServletRequestEvent sre) {
    }
}
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2、监听域对象的属性变化

（1）监听ServletContext属性的变化 – ServletContextAttributeListener

package javax.servlet;

import java.util.EventListener;

public interface ServletContextAttributeListener extends EventListener {
    default void attributeAdded(ServletContextAttributeEvent event) {
    }

    default void attributeRemoved(ServletContextAttributeEvent event) {
    }

    default void attributeReplaced(ServletContextAttributeEvent event) {
    }
}
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（2）监听HttpSession属性的变化 – HttpSessionAttributeListener

package javax.servlet.http;

import java.util.EventListener;

public interface HttpSessionAttributeListener extends EventListener {
    default void attributeAdded(HttpSessionBindingEvent event) {
    }

    default void attributeRemoved(HttpSessionBindingEvent event) {
    }

    default void attributeReplaced(HttpSessionBindingEvent event) {
    }
}
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（3）监听HttpServletRequest属性的变化 – ServletRequestAttributeListener

package javax.servlet;

import java.util.EventListener;

public interface ServletRequestAttributeListener extends EventListener {
    default void attributeAdded(ServletRequestAttributeEvent srae) {
    }

    default void attributeRemoved(ServletRequestAttributeEvent srae) {
    }

    default void attributeReplaced(ServletRequestAttributeEvent srae) {
    }
}
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3、监听session绑定javaBean

（1）监听javaBean对象是否绑定了session域 – HttpSessionBindingListener

package javax.servlet.http;

import java.util.EventListener;

public interface HttpSessionBindingListener extends EventListener {
    default void valueBound(HttpSessionBindingEvent event) {
    }

    default void valueUnbound(HttpSessionBindingEvent event) {
    }
}
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（2）监听javaBean对象的活化或钝化 --HttpSessionActivationListener

package javax.servlet.http;

import java.util.EventListener;

public interface HttpSessionActivationListener extends EventListener {
    default void sessionWillPassivate(HttpSessionEvent se) {
    }

    default void sessionDidActivate(HttpSessionEvent se) {
    }
}
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