HttpServletRequest有兩個重載的getSession()方法，一個接受一個boolean的類型的值，另一個不帶任何參數，getSession()方法和getSession(true)方法功能一樣，就是如果對應的客戶端已經產生過一個session，那么就會返回這個舊的session，否則，這個方法將會產生一個session ID并且和對應的客戶端綁定在一起，而如果getSession(false)表示如果對應的客戶端已經有對應的session，那么返回這個舊的session，否則不會產生新的session。可以使用HttpSession對象上的isNow()方法來判定這個session是否為新建的
?
<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">
?用戶名:
?<input type="text" name="username" /> <input type="submit" />
?密碼:
?<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 {
?//如果用戶輸入過了用戶名 則將其放在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已經創建");
?out.println("
");
?out.println("跳轉到其他<a>頁面</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 = "";
?//此處不是創建session 而是去取已經創建的session
?HttpSession session = request.getSession();
?//如果已經取到，說明已經登錄
?if(session!=null)
?{
?username = (String)session.getAttribute("username");
?out.println("獲得創建的Session");
?out.println("
");
?out.println("登錄名:"+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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