web服务器需要监控（web监听器）

一、简介Listener是Servlet规范的另一个高级特性，它用于监听java web程序的事件，例如创建、修改、删除session,request,context等，并触发相应的处理事件，这个处理事件是由web容器回掉的，接下来我们就来聊聊关于web服务器需要监控?以下内容大家不妨参考一二希望能帮到您!

web服务器需要监控

一、简介

Listener是Servlet规范的另一个高级特性，它用于监听java web程序的事件，例如创建、修改、删除session,request,context等，并触发相应的处理事件，这个处理事件是由web容器回掉的。

学过安卓开发的同学一定很熟悉view.setonClickLister();这样的对安卓控件的监听。java web也是这样的 ，根据不同的listner 和不同的event，可以完成相应的处理事件。

二、Listerner的分类

Listerner分为八种，前三种是用于监听对象的创建和销毁，中间三种用于监听对象属性的变化，后两种用于监听Session内对象。

• httpSessionListner: 监听session的创建与销毁，用于收集在线用户信息。
• servletContextListener:监听context的创建与销毁，context代表当前web应用，该listener可用于启动时获取web.xml的初始化参数。
• servletRequestListener: 监听request 的创建与销毁。
• httpSessionAttributeListener 监听session的种属性变化
• ServletContextAttributeListener
• ServletRequestAttributeListener
• HttpSessionBindingListener,监听对象存入或者移除 session
• httpSessionActivationListener,钝化和重新加载 session的监听

三、监听session、request、servletContext

直接上代码，下面监听了这三个对象创建销毁。

public class ListenerTest implements HttpSessionListener ,ServletContextListener,ServletRequestListener{ Log log=LogFactory.getLog(getClass()); public void requestDestroyed(ServletRequestEvent sre) { HttpServletRequest request=(HttpServletRequest) sre.getServletRequest(); long time=System.currentTimeMillis()-(Long)request.getAttribute("time"); log.info("请求处理时间" time); } public void requestInitialized(ServletRequestEvent sre) { HttpServletRequest request=(HttpServletRequest) sre.getServletRequest(); String uri=request.getRequestURI(); uri=request.getQueryString()==null?uri:(uri "?" request.getQueryString()); log.info("ip" request.getRemoteAddr() uri); request.setAttribute("time", System.currentTimeMillis()); } public void contextDestroyed(ServletContextEvent sce) { ServletContext servletContext=sce.getServletContext(); log.info("关闭：" servletContext.getContextPath()); } public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext=sce.getServletContext(); log.info("启动：" servletContext.getContextPath()); } public void sessionCreated(HttpSessionEvent se) { HttpSession session=se.getSession(); log.info("创建：session:" session.getId()); } public void sessionDestroyed(HttpSessionEvent se) { HttpSession session=se.getSession(); log.info("销毁建：session:" session.getId()); } }

需要在web.xml中配置：

<listener> <listener-class>com.forezp.listener.ListenerTest</listener-class> </listener>

四、监听对象属性的变化

• httpSessionAttributeListener 监听session的种属性变化
• ServletContextAttributeListener
• ServletRequestAttributeListener

以上三种方法用于监听session ,context,request的属性发生变化，例如添加、更新、移除。 下面以session的属性变化为例子：

public class SessionAttributeListener implements HttpSessionAttributeListener{ Log log=LogFactory.getLog(getClass()); public void attributeAdded(HttpSessionBindingEvent se) { HttpSession httpSession=se.getSession(); log.info("新建属性：" se.getName() "值：" se.getValue()); } public void attributeRemoved(HttpSessionBindingEvent se) { HttpSession httpSession=se.getSession(); log.info(" 删除属性：" se.getName() "值：" se.getValue()); } public void attributeReplaced(HttpSessionBindingEvent se) { HttpSession httpSession=se.getSession(); log.info(" 修改属性：" se.getName() "原来的值：" se.getValue() "新值：" httpSession.getAttribute(se.getName())); } }

web.xml配置，此处省略。

五、监听session内的对象

• HttpSessionBindingListener,当对象被放到session里执行valueBond();当对象被移除，执行valueUnbond();
• httpSessionActivationListener,服务器关闭,会将session的内容保存在硬盘里，这个过程叫钝化；服务器重启，会将session的内容从硬盘中重新加载。钝化时执行sesionWillPassivate(),重新加载sessionDidActivate();

举个例子：

public class User implements HttpSessionBindingListener,HttpSessionActivationListener,Serializable {

private String username;

private String password;

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;

}

public String getPassword() {

return password;

}

public void setPassword(String password) {

this.password = password;

}

//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());

}

}

init.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme() "://" request.getServerName() ":" request.getServerPort() path "/";

request.getSession().setAttribute("currentUser", new com.forezp.entity.User());

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

<base href="<%=basePath%>">

<title>My JSP 'init.jsp' starting page</title>

<meta http-equiv="pragma" content="no-cache">

<meta http-equiv="cache-control" content="no-cache">

<meta http-equiv="expires" content="0">

<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

<meta http-equiv="description" content="This is my page">

<!--

<link rel="stylesheet" type="text/css" href="styles.css">

-->

</head>

<body>

这是初始化值的界面

<button onclick="location.href='<%=request.getContextPath()%>/init.jsp';">Init</button>

<button onclick="location.href='<%=request.getContextPath()%>/destory.jsp';">Destory</button>

</body>

</html>

destroy.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme() "://" request.getServerName() ":" request.getServerPort() path "/"; request.getSession().removeAttribute("currentUser"); %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP 'destory.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> </head> <body> 这是销毁界面 <button onclick="location.href='<%=request.getContextPath()%>/init.jsp';">Init</button> <button onclick="location.href='<%=request.getContextPath()%>/destory.jsp';">Destory</button> </body> </html>

当访问init.jsp，再访问destroy.jsp;再访问init,jsp，再关闭服务器，重启；log日志如下：

valueBound Name:currentUser

valueUnbound Name:currentUser

sessionWillPassivate org.apache.catalina.session.StandardSessionFacade@33f3be1

sessionDidActivate org.apache.catalina.session.StandardSessionFacade@33f3be1

六、显示在线人数：

@WebListener public class MyHttpSessionListener implements HttpSessionListener { private int userNumber = 0; @Override public void sessionCreated(HttpSessionEvent arg0) { userNumber ; arg0.getSession().getServletContext().setAttribute("userNumber", userNumber); } @Override public void sessionDestroyed(HttpSessionEvent arg0) { userNumber--; arg0.getSession().getServletContext().setAttribute("userNumber", userNumber); } }

jsp中显示：

<body> 当前在线用户人数:${userNumber }<br/> </body>

这是一个简答的统计在线人数的方法，如果你需要知道这些人来自哪里，需要配合httpRequestListener配合，也可以实现单登陆，在这里不写代码了。

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