JavaWeb -- sevlet 监听器

1.三个域对象的监听（创建和销毁） servletContext, session, request 监听器

ServletContext监听器：

public class MyServletContextListener implements ServletContextListener {

@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("Context 初始化");
}

@Override
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("Context 销毁");
}

}

web.xml 配置

<listener>
<listener-class>com.kevin.web.listener.MyServletContextListener</listener-class>
</listener>

Session监听器：

public class MyHttpSessionListener implements HttpSessionListener {

@Override
public void sessionCreated(HttpSessionEvent se) {
System.out.println("Session 创建");

}

@Override
public void sessionDestroyed(HttpSessionEvent se) {
System.out.println("Session 摧毁");
}

}

Request监听器：

public class MyServletRequestListener implements ServletRequestListener {

@Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("request 创建");

}

@Override
public void requestDestroyed(ServletRequestEvent sre) {
System.out.println("request 销毁");

}
}

监听器还可以监听三个域中所添加的属性变化：

public class MyServletContextAttributeListener implements
ServletContextAttributeListener {

public void attributeAdded(ServletContextAttributeEvent scab) {

System.out.println(scab.getValue());
System.out.println("加东西了！！");

}

public void attributeRemoved(ServletContextAttributeEvent scab) {
System.out.println("删东西了！！");
}

public void attributeReplaced(ServletContextAttributeEvent scab) {
System.out.println("替换东西了！！");
}
}

public class MyRequestAndSessionAttributeListener implements
HttpSessionAttributeListener, ServletRequestAttributeListener {

public void attributeAdded(HttpSessionBindingEvent se) {
System.out.println("session中加东西了！！");
}

public void attributeRemoved(HttpSessionBindingEvent se) {
System.out.println("session中删东西了！！");
}

public void attributeReplaced(HttpSessionBindingEvent se) {
System.out.println("session中替换东西了！！");
}

public void attributeAdded(ServletRequestAttributeEvent srae) {
System.out.println("request中加东西了！！");
}

public void attributeRemoved(ServletRequestAttributeEvent srae) {
System.out.println("request中删东西了！！");
}

public void attributeReplaced(ServletRequestAttributeEvent srae) {
System.out.println("request中替换东西了！！");
}
}

HttpSessionBindingListener HttpSessionActivationListener 这两个监听器 不需要再web.xml文件中配置

public class MyBean implements HttpSessionBindingListener {

private String name;

public void valueBound(HttpSessionBindingEvent event) {
System.out.println("自己被加到session中了");
}

public void valueUnbound(HttpSessionBindingEvent event) {
System.out.println("自己被session踢出来了");
}
}

public class MyBean2 implements HttpSessionActivationListener,Serializable {

public void sessionDidActivate(HttpSessionEvent se) {
System.out.println("session从硬盘回到内存了");
}

public void sessionWillPassivate(HttpSessionEvent se) {
System.out.println("session被序列化到硬盘了");
}
}

2. 实例： 在线人数计数器

public class OnLineCountListener implements HttpSessionListener {

@Override
public void sessionCreated(HttpSessionEvent se) {

ServletContext context =  se.getSession().getServletContext();
Integer num = (Integer) context.getAttribute("num");
if(num==null)
context.setAttribute("num", 1);
else
{
num++;
context.setAttribute("num", num);
}

}

@Override
public void sessionDestroyed(HttpSessionEvent se) {

ServletContext context =  se.getSession().getServletContext();
Integer num = (Integer) context.getAttribute("num");
if(num==null)
context.setAttribute("num", 1);
else
{
num--;
context.setAttribute("num", num);
}
}

}

3. 实例： 自定义session扫描器

public class SessionScanerListener implements HttpSessionListener,ServletContextListener {

private List<HttpSession> list = Collections.synchronizedList( new LinkedList<HttpSession>());
private Integer lock = 0;

@Override
public void contextInitialized(ServletContextEvent sce) {
Timer timer = new Timer();
timer.schedule(new MyTask(list, lock) , 0, 1000*15);

}

@Override
public void sessionCreated(HttpSessionEvent se) {
HttpSession session =  se.getSession();
synchronized (lock) {
list.add(session);
}
System.out.println(session + "创建了");
}

@Override
public void sessionDestroyed(HttpSessionEvent se) {
HttpSession session =  se.getSession();
System.out.println(session + "销毁了");
}

@Override
public void contextDestroyed(ServletContextEvent sce) {
// TODO Auto-generated method stub

}
}

class MyTask extends TimerTask
{
private List<HttpSession> list;
private Integer lock;

public MyTask(List<HttpSession> list, Integer lock)
{
this.list = list;
this.lock = lock;
}

@Override
public void run() {

synchronized (lock) {
System.out.println("定时器启动了");
ListIterator<HttpSession> it = list.listIterator();
while(it.hasNext())
{
HttpSession session = it.next();
if(System.currentTimeMillis()-session.getLastAccessedTime() > 1000*15)
{
session.invalidate();
list.remove(session);
}
}
}
}
}