目录
ServletContextAttributeListener 监听器
WyxServletContextAttributeListener.java
HttpSessionAttributeListener 监听器
ServletRequestAttributeListener 监听器
JavaWeb 三大组件之监听器 Listener
Listener 监听器介绍
1. Listener 监听器它是 JavaWeb 的三大组件之一。JavaWeb 的三大组件分别是：Servlet 程序、Listener 监听器、Filter 过滤器
2. Listener 是 JavaEE 的规范，就是接口
3. 监听器的作用是，监听某种变化(一般就是对象创建/销毁, 属性变化), 触发对应方法完成相应的任务
JavaWeb 的监听器
ServletContextListener 监听器
1. 作用：监听 ServletContext 创建或销毁(当我们 Web 应用启动时，就会创建 ServletContext)，
即生命周期监听，应用场景
(1)加载初始化的配置文件；比如 spring 的配置文件
(2)任务调度（配合定时器 Timer/TimerTask)
相关方法
代码演示
wyxServletContextListener
/**
* 1. 当一个类实现了 ServletContextListener
* 2. 该类就是一个监听器
* 3. 该类可以监听的事件 由该类实现的监听接口决定 ，比如 实现ServletContextListener
* , 则该类就可以监听 ServletContext对象的创建和销毁, 以此类推
* 4. wyxServletContextListener 就是一个监听者
* 5. 当web应用启动时，就会产生 ServletContextEvent 事件, 会调用监听器的对应事件处理方法
* contextInitialized, 同时会传递 事件对象
* 6. 程序员可以通过 ServletContextEvent 事件对象，来获取需要的信息, 然后再进行业务处理
* 7. tomcat怎么知道这个监听器存在 ? 因为我们需要在web.xml中配置
*/
public class wyxServletContextListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
ServletContext servletContext = servletContextEvent.getServletContext();
System.out.println("HspServletContextListener 监听到 " +
servletContext + " 被创建..");
//如果我们获取到ServletContext 对象..进行业务处理
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
ServletContext servletContext = servletContextEvent.getServletContext();
System.out.println("HspServletContextListener 监听到 " +
servletContext + " 被销毁..");
//比如可以对servletContext 数据进行处理， 或者日志的管理...
System.out.println("进行处理工作.....");
}
}xml配置
<listener>
<listener-class>com.wyx.listener.WyxServletContextListener</listener-class>
</listener>ServletContextAttributeListener 监听器
1. 作用：监听 ServletContext 属性变化
相关方法
代码示例
WyxServletContextAttributeListener.java
public class WyxServletContextAttributeListener implements ServletContextAttributeListener {
@Override
public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("WyxServletContextAttributeListener 监听到添加属性.."
+ servletContextAttributeEvent.getName() + "=" + servletContextAttributeEvent.getValue() );
}
@Override
public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("WyxServletContextAttributeListener 监听到删除属性.."
+ servletContextAttributeEvent.getName() + "=" + servletContextAttributeEvent.getValue() );
}
@Override
public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("WyxServletContextAttributeListener 监听到修改属性.."
+ servletContextAttributeEvent.getName() + "=" + servletContextAttributeEvent.getValue() );
}
}TestServlet.java
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class TestServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
getServletContext().setAttribute("k1","k1_value");
}
}xml配置
<listener>
<listener-class>com.wyx.listener.WyxHttpSessionAttributeListener</listener-class>
</listener>HttpSessionListener 监听器
1. 作用：监听 Session 创建或销毁，即生命周期监听
2. 相关方法
3. 使用方法和前面一样, 可以用于监控用户上线，离线
代码示例
public class WyxHttpSessionListener implements HttpSessionListener {
@Override
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
HttpSession session = httpSessionEvent.getSession();
//当session创建时，我们给它设置一个生命周期 30s
session.setMaxInactiveInterval(30);
System.out.println("WyxHttpSessionListener 监听到 session创建= " +
session.getId());
System.out.println("用户id=" + session.getId() + " 上线");
}
@Override
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
HttpSession session = httpSessionEvent.getSession();
System.out.println("WyxHttpSessionListener 监听到 session销毁= " +
session.getId());
System.out.println("用户id=" + session.getId() + " 离线");
}
}xml配置与前面一样
HttpSessionAttributeListener 监听器
1. 作用：监听 Session 属性的变化
2. 相关方法
代码示例
public class WyxHttpSessionAttributeListener implements HttpSessionAttributeListener {
@Override
public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
//HttpSession session = httpSessionBindingEvent.getSession();
System.out.println("WyxHttpSessionAttributeListener 监听到session添加属性" +
httpSessionBindingEvent.getName() + "=" + httpSessionBindingEvent.getValue());
}
@Override
public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
HttpSession session = httpSessionBindingEvent.getSession();
System.out.println("WyxHttpSessionAttributeListener 监听到session删除属性" +
httpSessionBindingEvent.getName());
}
@Override
public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
System.out.println("WyxHttpSessionAttributeListener 监听到session修改属性" +
httpSessionBindingEvent.getName() + "=" + httpSessionBindingEvent.getValue());
}
}xml配置与前面一样
ServletRequestListener 监听器
1. ServletRequestListener 监听器
2. 作用：监听 Request 创建或销毁，即 Request 生命周期监听
相关方法
3. 可以用来监控, 某个 IP 访问我们网站的频率, 日志记录 ,访问资源的情况
代码示例
public class WyxRequestListener implements ServletRequestListener {
@Override
public void requestInitialized(ServletRequestEvent servletRequestEvent) {
System.out.println("WyxRequestListener 监听到 request对象创建");
ServletRequest servletRequest = servletRequestEvent.getServletRequest();
System.out.println("记录访问日志....");
System.out.println("访问IP= " + servletRequest.getRemoteAddr());
System.out.println("访问的资源= " + ((HttpServletRequest)servletRequest).getRequestURL());
}
@Override
public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
System.out.println(" WyxRequestListener 监听到 request对象被销毁");
}
}ServletRequestAttributeListener 监听器
1. 作用：监听 Request 属性变化
2. 相关方法
代码示例
public class WyxServletContextAttributeListener implements ServletContextAttributeListener {
@Override
public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("WyxServletContextAttributeL istener 监听到添加属性.."
+ servletContextAttributeEvent.getName() + "=" + servletContextAttributeEvent.getValue() );
}
@Override
public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("WyxServletContextAttributeListener 监听到删除属性.."
+ servletContextAttributeEvent.getName() + "=" + servletContextAttributeEvent.getValue() );
}
@Override
public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("WyxServletContextAttributeListener 监听到修改属性.."
+ servletContextAttributeEvent.getName() + "=" + servletContextAttributeEvent.getValue() );
}
}
HttpSessionBindingListener 感知监听器
HttpSessionActivationListener 感知监听器
不常用了解即可
