HttpServletRequest有两个重载的getSession()方法，一个接受一个boolean的类型的值，另一个不带任何参数，getSession()方法和getSession(true)方法功能一样，就是如果对应的客户端已经产生过一个session，那么就会返回这个旧的session，否则，这个方法将会产生一个session ID并且和对应的客户端绑定在一起，而如果getSession(false)表示如果对应的客户端已经有对应的session，那么返回这个旧的session，否则不会产生新的session。可以使用HttpSession对象上的isNow()方法来判定这个session是否为新建的
<meta name="keywords" content="keyword1,keyword2,keyword3" />
<meta name="description" content="this is my page" />
<meta name="content-type" content="text/html; charset=UTF-8" />
<!-- <link rel="stylesheet" type="text/css" href="./styles.css">--></pre>
<form action="servlet/saveinfo" method="post">
用户名:
<input type="text" name="username" /> <input type="submit" />
密码:
<input type="password" name="userpasswd" />
</form>
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</pre>
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package chap03;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class saveinfo extends HttpServlet {
/**
* Constructor of the object.
*/
public saveinfo() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//如果用户输入过了用户名 则将其放在session中
if(request.getParameter("username")!=null);
{
HttpSession session = request.getSession();
session.setAttribute("username",request.getParameter("username"));
}
response.setContentType("text/html;charset=GBK");
PrintWriter out = response.getWriter();
out.println("session已经创建");
out.println("
");
out.println("跳转到其他<a>页面</a>");
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}</pre>
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package chap03;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class getsession extends HttpServlet {
/**
* Constructor of the object.
*/
public getsession() {
super();
}
/**
* Destruction of the servlet.
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet.
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=GBK");
PrintWriter out = response.getWriter();
String username = "";
//此处不是创建session 而是去取已经创建的session
HttpSession session = request.getSession();
//如果已经取到，说明已经登录
if(session!=null)
{
username = (String)session.getAttribute("username");
out.println("获得创建的Session");
out.println("
");
out.println("登录名:"+username);
}
else
{
response.sendRedirect("../sessionlogin.html");
}
}
/**
* The doPost method of the servlet.
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
/**
* Initialization of the servlet.
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}</pre>
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