应用Session与Application-优快云博客

一、application

application实现用户之间的数据共享
application对象的常用方法

实例：统计网站访问次数

思路：

去除application中原始计数器的值
判断计数器的值，若存在则累加1；不存在则设置为1
使用application保存计数器
在页面显示计数器的值

<body>
	<%
       //获得application的数据
       Integer in = (Integer)application.getAttribute("count");
       if(in == null){
        in = 1;
       }else{
        in+=1;
       }
       application.setAttribute("count", in);   
     %>
	网站访问次数：<%=in %>
</body>

小结：

作用域：

page：作用在当前页面
request：作用对象与客户端的请求绑定在一起
session：作用在整个会话范围内

实例：使用application创建一个聊天室

源码：源码

<%@ page language="java" pageEncoding="gb2312"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>欢迎进入聊天室</title>
</head>
<body>
	<h1>欢迎进入聊天室</h1>
	<form action="dochat.jsp" method="post">
	 帐号:<input type="text" name="username" />
	 <input type="submit" value="确认" />
	</form>
</body>
</html>

dochat.jsp

<%
	request.setCharacterEncoding("utf-8");
	String name = request.getParameter("username");
	String msg = request.getParameter("msg");
	//获得application存储的内容
	//使用集合来存取信息
	List list = (List) application.getAttribute("msg");
	//第一次进去的时候集合为空，所以创建一个集合数组
	if (list == null) {
		list = new ArrayList();
	}
	if (msg != null) {
	//trim()用来消除空格
		msg = name + "说:" + msg.trim() + "\n";
		list.add(msg);
	}
	//把聊天内容list存储在application中
	application.setAttribute("msg", list);
	response.sendRedirect("chat.jsp?username="+name);
%>

chat.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
	String path = request.getContextPath();
	String basePath = request.getScheme() + "://"
			+ request.getServerName() + ":" + request.getServerPort()
			+ path + "/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'chat.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">
<script type="text/javascript">
	function check() {

		var content = document.getElementById("msg").value;
		if (content == "") {
			alert("请输入聊天内容");
			document.getElementById("msg").focus();
			return false;
		}
	}
</script>
</head>
<body>
<h1>开心聊天室欢迎您</h1>
	<textarea rows="30" cols="80"><%
	String name = request.getParameter("username");
	//获得application存储的内容
	List list = (List) application.getAttribute("msg");
  	if(list!=null){
  	for (int i = 0; i < list.size(); i++) {
  		String message = (String) list.get(i);
  		if (message != null) {
  			out.print(message);
  		}
  	}
  	}
  %>
  </textarea>	
	<form action="dochat.jsp" method="post" οnsubmit="return check()">
		请输入聊天内容:<input type="text" name="msg" id="msg">
		<input type="hidden" name="username"  value=<%=name%>>
		 <input type="submit" value="提交">
	</form>
</body>
</html>

JSP的内置对象二