Jsp内置对象
重点：
各个对象的生命周期
各种页面间传值的方式
Jsp有九个内置对象，包括：
对象名 类型 作用域
request javax.servlet.ServletRequest Request
response javax.servlet.ServletResponse Page
pageContext javax.servlet.jsp.PageContext Page
session javax.servlet.http.HttpSession Session
application javax.servlet.SevletContext Application
out javax.servlet.jsp.JspWriter Page
config javax.servlet.ServletConfig Page
page java.lang.Object Page
exception java.lang.Throwable Page
***********************************************************************
主要的三个对象
request
主要的方法有：
String getParameter(String name) 多用于值唯一的情况
Enumeration getParameterNames()
String[] getParameterValues(String name) 多用于值有多个时，比如复选框里的勾选内容
Object getAttribute(String name) 用于用户向服务器端发出请求时，传递参数，必须是同一个请求时才有效。可以一次请求多页面传递。
用户的每一个请求都会产生一个request对象。请求结束时，request对象被销毁，也就没有attribute了。当发出下一个请求时，生成了另外一个request对象。
void setAttribute(String name,Object o)
request1.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'request1.jsp' starting page</title>
</head>
<body>
<form action="request2.jsp">
username:
<input type="text" name="username"/><br>
<input type="submit" value="submit"/>
</form>
</body>
</html>
|
Request2.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'request2.jsp' starting page</title>
</head>
<body>
<%
String username = request.getParameter("username");
request.setAttribute("username",username);
%>
username: <%=username %>
<jsp:forward page="request3.jsp"></jsp:forward>
</body>
</html> |
Request3.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'request3.jsp' starting page</title>
</head>
<body>
<%
String username = (String)request.getAttribute("username");
%>
<%=username %>
</body>
</html>
|
session
http是无状态的协议
web server对每一个客户端的请求都没有历史记忆
session用来保存当前客户端状态信息
主要的方法有：
Object getAttribute(String name)
void setAttribute(String name,Object value)
只要当前连接没有关闭，或session没有到期，session里的数据就不丢失（序列化到硬盘的情况除外）
session1.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'session1.jsp' starting page</title>
</head>
<body>
<form action="session2.jsp">
username:
<input type="text" name="username"/><br>
<input type="submit" value="submit"/>
</form>
</body>
</html>
|
Session2.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'session2.jsp' starting page</title>
</head>
<body>
<%
String username = request.getParameter("username");
session.setAttribute("name",username);
%>
your name "<%=username %>" is saved in session<br>
<a href="session3.jsp?name=<%=username %>">check</a>
</body>
</html> |
Session3.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'session3.jsp' starting page</title>
</head>
<body>
<%
String username = (String)session.getAttribute("name");
if(username == null)
{
out.println("你还没有登录");
}
else
{
out.println(username + "已经登录");
}
%>
</body>
</html> |
执行结果
application
Object getAttribute(String name)
void setAttribute(String name,Object object)
application.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'application.jsp' starting page</title>
</head>
<body>
<%
int count = 0;
if(application.getAttribute("count")==null)
{
application.setAttribute("count",1);
count = 1;
}
else
{
String icount = application.getAttribute("count").toString();
count = Integer.parseInt(icount);
count++;
application.setAttribute("count",count);
}
out.println("你是第"+count +"个访问者");
%>
</body>
</html>
|
存活范围最大的对象，只要服务器没有关闭，application的数据会一直存在，会被所有的用户共享。
其他常用的方法
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'application2.jsp' starting page</title>
</head>
<body>
<%
out.println("java servlet API version: <b>"
+ application.getMajorVersion() + "."
+ application.getMinorVersion() + "</b><br>");
out.println("URL of 'application2.jsp' is: <b>"
+ application.getResource("/application2.jsp")
+ "</b><br>");
out.println("getServerInfo() = <b>" + application.getServerInfo() + "</b><br>");
out.println("<b>" + application.getRealPath(" ") + "</b>");
%>
</body>
</html>
|
输出结果为：
| java servlet API version: 2.5 |
Forward机制
<jsp:forward>
会将用户的请求转发到其他页面，传递的是始终是同一个请求。
在请求期间，可以用request对象传递数据，但是请求结束，数据就会销毁。
myForward.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'myForward.jsp' starting page</title>
</head>
<body>
<form action="MyFormServlet">
username:
<input type="text" name="username"/><br>
<input type="submit" value="submit"/>
</form>
</body>
</html>
|
MyFormServlet.jsp
| public class MyFormServlet extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
String username= request.getParameter("username");
request.setAttribute("username",username);
List<String> list = new ArrayList<String>();
for(int i=0;i<100;i++)
{
list.add(i+"");
}
request.setAttribute("list",list);
RequestDispatcher rd = request.getRequestDispatcher("myresult.jsp");
rd.forward(request,response);
}
} |
Myresult.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'myresult.jsp' starting page</title>
</head>
<body>
username:
<%=request.getAttribute("username")%>
<br>
<%
List<String> list = (List<String>) request.getAttribute("list");
for (int i = 0; i < list.size(); i++)
{
out.println(list.get(i) + "<br>");
}
%>
</body>
</html> |
Servlet主要进行流程处理，包括派发请求并增加额外处理等。
jsp主要处理页面显示的问题。
************************************************************************
Asp.net常用的页面传值的方式：(也是实际开发中常用的方式)
<input type=”hidden”/>
Hidden1.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'hidden1.jsp' starting page</title>
</head>
<body>
<form action="hidden2.jsp" method="post">
please input your name:
<input type="text" name="username" />
<input type="submit" value="submit" />
</form>
</body>
</html>
|
Hidden2.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'hidden2.jsp' starting page</title>
</head>
<body>
<%
String username = request.getParameter("username");
%>
username:
<%=username%>
<form method="post" action="hidden3.jsp">
please input your like:
<input type="text" name="like" />
<input type="hidden" name="username" value="<%=username%>" />
<input type="submit" value="submit"/>
</form>
</body>
</html>
|
Hidden3.jsp
| <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'hidden3.jsp' starting page</title>
</head>
<body>
<%
String username = request.getParameter("username");
String like = request.getParameter("like");
%>
your name is :
<%=username%>
<br/>
your like is :
<%=like%>
</body>
</html>
|