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servlet中session簡(jiǎn)介和使用例子

更新時(shí)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(gè)接口中的，這個(gè)接口是構(gòu)建在cookie或者URL重寫(xiě)的基礎(chǔ)上,要得到一個(gè)HttpSession的實(shí)例，就可以通過(guò)HttpServletRequest的getSession()方法來(lái)獲得

HttpServletRequest有兩個(gè)重載的getSession()方法，一個(gè)接受一個(gè)boolean的類型的值，另一個(gè)不帶任何參數(shù)，getSession()方法和getSession(true)方法功能一樣，就是如果對(duì)應(yīng)的客戶端已經(jīng)產(chǎn)生過(guò)一個(gè)session，那么就會(huì)返回這個(gè)舊的session，否則，這個(gè)方法將會(huì)產(chǎn)生一個(gè)session ID并且和對(duì)應(yīng)的客戶端綁定在一起，而如果getSession(false)表示如果對(duì)應(yīng)的客戶端已經(jīng)有對(duì)應(yīng)的session，那么返回這個(gè)舊的session，否則不會(huì)產(chǎn)生新的session。可以使用HttpSession對(duì)象上的isNow()方法來(lái)判定這個(gè)session是否為新建的

HttpSession常用方法

public void setAttribute(String name,Object value)
將value對(duì)象以name名稱綁定到會(huì)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(huì)話中刪除name屬性，如果不存在不會(huì)執(zhí)行，也不會(huì)拋處錯(cuò)誤.

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

public void invalidate()
使會(huì)話失效，同時(shí)刪除屬性對(duì)象

public Boolean isNew()
用于檢測(cè)當(dāng)前客戶是否為新的會(huì)話

public long getCreationTime()
返回會(huì)話創(chuàng)建時(shí)間

public long getLastAccessedTime()
返回在會(huì)話時(shí)間內(nèi)web容器接收到客戶最后發(fā)出的請(qǐng)求的時(shí)間

public int getMaxInactiveInterval()
返回在會(huì)話期間內(nèi)客戶請(qǐng)求的最長(zhǎng)時(shí)間為秒

public void setMaxInactiveInterval(int seconds)
允許客戶客戶請(qǐng)求的最長(zhǎng)時(shí)間

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

public String getId()
返回會(huì)話期間的識(shí)別號(hào)

一個(gè)保存信息到session的簡(jiǎn)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(guò)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(yè)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(shuō)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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