按监听的对象划分
1.用于监听应用程序环境对象（ServletContext）的事件监听器，实现ServletContextListener接口
public class MyServletContextListener implements ServletContextListener {
public void contextInitialized(ServletContextEvent servletcontextevent) {
String initParam = servletcontextevent.getServletContext().getInitParameter("initParam");
System.out.println("contextInitialized : initParam = "+initParam);
}
public void contextDestroyed(ServletContextEvent servletcontextevent) {
System.out.println("contextDestroyed");
}
}
2.用于监听用户会话对象（HttpSession）的事件监听器，实现HttpSessionListener接口
public class MyHttpSessionListener implements HttpSessionListener {
public void sessionCreated(HttpSessionEvent httpsessionevent) {
System.out.println("sessionCreated");
}
public void sessionDestroyed(HttpSessionEvent httpsessionevent) {
System.out.println("sessionDestroyed");
}
}
3.用于监听请求消息对象（ServletRequest）的事件监听器，实现ServletRequestListener接口
public class MyServletRequestListener implements ServletRequestListener {
public void requestDestroyed(ServletRequestEvent servletrequestevent) {
System.out.println("requestDestroyed ");
}
public void requestInitialized(ServletRequestEvent servletrequestevent) {
String name = servletrequestevent.getServletRequest().getParameter("name");
System.out.println("requestInitialized name:"+name);
}
}
按监听的事件划分
1.监听域对象自身的创建和销毁的事件监听器
即按监听对象划分的那几种
2.监听域对象的属性的增加和删除的事件监听器，实现ServletContextAttributeListener，HttpSessionAttributeListener 或 ServletRequestAttributeListener接口
public class MyServletContextAttributeListener implements ServletContextAttributeListener {
public void attributeAdded(ServletContextAttributeEvent servletcontextattributeevent) {
System.out.println("ServletContext_attributeAdded:"+servletcontextattributeevent.getName());
}
public void attributeRemoved(ServletContextAttributeEvent servletcontextattributeevent) {
System.out.println("ServletContext_attributeRemoved:"+servletcontextattributeevent.getName());
}
public void attributeReplaced(ServletContextAttributeEvent servletcontextattributeevent) {
System.out.println("ServletContext_attributeReplaced:"+servletcontextattributeevent.getName());
}
}
HttpSession和ServletRequest同理，只是方法参数类型不同
3.监听绑定到HttpSession域中的某个对象的状态的事件监听器
这种情况不需要专门设计一个作为监听器的类，可以作为一个实体类，然后继承需要的接口：
public class User implements HttpSessionBindingListener,HttpSessionActivationListener,Serializable {
private String username;
public void valueBound(HttpSessionBindingEvent httpsessionbindingevent) {
System.out.println("valueBound Name:"+httpsessionbindingevent.getName());
}
public void valueUnbound(HttpSessionBindingEvent httpsessionbindingevent) {
System.out.println("valueUnbound Name:"+httpsessionbindingevent.getName());
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
//钝化
public void sessionWillPassivate(HttpSessionEvent httpsessionevent) {
System.out.println("sessionWillPassivate "+httpsessionevent.getSource());
}
//活化
public void sessionDidActivate(HttpSessionEvent httpsessionevent) {
System.out.println("sessionDidActivate "+httpsessionevent.getSource());
}
}
绑定和解除绑定：实现HttpSessionBindingListener接口
钝化和活化：实现HttpSessionActivationListener和Serializable接口
实现
Serializable接口是因为钝化时需要将seesion序列化存储到文件或者数据库，活化时需要反序列化
