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servlet中session簡介和使用例子

更新時間：2014年04月23日 10:39:13 作者：

在servlet中,session是封裝在javax.servlet.http.HttpSession這個接口中的，這個接口是構(gòu)建在cookie或者URL重寫的基礎(chǔ)上,要得到一個HttpSession的實(shí)例，就可以通過HttpServletRequest的getSession()方法來獲得

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(shù)，getSession()方法和getSession(true)方法功能一樣，就是如果對應(yīng)的客戶端已經(jīng)產(chǎn)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(chǎn)生一個session ID并且和對應(yīng)的客戶端綁定在一起，而如果getSession(false)表示如果對應(yīng)的客戶端已經(jīng)有對應(yīng)的session，那么返回這個舊的session，否則不會產(chǎn)生新的session?？梢允褂肏ttpSession對象上的isNow()方法來判定這個session是否為新建的

HttpSession常用方法

public void setAttribute(String name,Object value)
將value對象以name名稱綁定到會話

public object getAttribute(String name)
取得name的屬性值，如果屬性不存在則返回null

public void removeAttribute(String name)
從會話中刪除name屬性，如果不存在不會執(zhí)行，也不會拋處錯誤.

public Enumeration getAttributeNames()
返回和會話有關(guān)的枚舉值

public void invalidate()
使會話失效，同時刪除屬性對象

public Boolean isNew()
用于檢測當(dāng)前客戶是否為新的會話

public long getCreationTime()
返回會話創(chuàng)建時間

public long getLastAccessedTime()
返回在會話時間內(nèi)web容器接收到客戶最后發(fā)出的請求的時間

public int getMaxInactiveInterval()
返回在會話期間內(nèi)客戶請求的最長時間為秒

public void setMaxInactiveInterval(int seconds)
允許客戶客戶請求的最長時間

ServletContext getServletContext()
返回當(dāng)前會話的上下文環(huán)境，ServletContext對象可以使Servlet與web容器進(jìn)行通信

public String getId()
返回會話期間的識別號

一個保存信息到session的簡單例子

sessionlogin.html

復(fù)制代碼代碼如下:

復(fù)制代碼代碼如下:

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(jīng)創(chuàng)建");
 out.println("
");
 out.println("跳轉(zhuǎn)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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復(fù)制代碼代碼如下:

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(chuàng)建session 而是去取已經(jīng)創(chuàng)建的session
 HttpSession session = request.getSession();
 //如果已經(jīng)取到，說明已經(jīng)登錄
 if(session!=null)
 {
 username = (String)session.getAttribute("username");
 out.println("獲得創(chuàng)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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