在本節(jié)中,我們將介紹Servlet中的HttpSession對(duì)象的使用,在應(yīng)用容器中,它為每個(gè)用戶創(chuàng)建會(huì)話ID。容器使用此標(biāo)識(shí)來(lái)識(shí)別特定的用戶。HttpSession的一個(gè)對(duì)象可用于執(zhí)行兩個(gè)任務(wù):
如何獲取HttpSession對(duì)象?
HttpServletRequest
接口提供了兩種獲取HttpSession
對(duì)象的方法:
public HttpSession getSession()
:返回與此請(qǐng)求相關(guān)聯(lián)的當(dāng)前會(huì)話,或者如果請(qǐng)求沒(méi)有會(huì)話,則創(chuàng)建一個(gè)會(huì)話。public HttpSession getSession(boolean create)
: 返回與此請(qǐng)求相關(guān)聯(lián)的當(dāng)前HttpSession
,如果沒(méi)有當(dāng)前會(huì)話,并且create
的值為true
,則返回一個(gè)新會(huì)話。HttpSession接口的常用方法
public String getId()
- 返回一個(gè)包含唯一標(biāo)識(shí)符值的字符串。public long getCreationTime()
- 返回創(chuàng)建此會(huì)話的時(shí)間,以1970年1月1日GMT格林尼治時(shí)間以來(lái)的毫秒為單位。public long getLastAccessedTime()
- 返回客戶端發(fā)送與此會(huì)話相關(guān)聯(lián)的請(qǐng)求的最后一次,為1970年1月1日GMT以來(lái)的毫秒數(shù)。public void invalidate()
- 使此會(huì)話無(wú)效,然后取消綁定綁定到該對(duì)象的任何對(duì)象。在本示例中,我們將在會(huì)話范圍中的屬性設(shè)置在一個(gè)servlet中,并從另一個(gè)servlet中的會(huì)話范圍獲取該值。要在會(huì)話范圍內(nèi)設(shè)置屬性,可使用HttpSession
接口的setAttribute()
方法設(shè)置屬性,并使用getAttribute()
方法獲取屬性。
打開(kāi)Eclipse,創(chuàng)建一個(gè)動(dòng)態(tài)Web項(xiàng)目:HttpSession,其完整的目錄結(jié)構(gòu)如下所示 -
以下是這個(gè)項(xiàng)目中的幾個(gè)主要的代碼文件。
文件:index.html -
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>HttpSession會(huì)話跟蹤示例</title>
</head>
<body>
<div style="text-algin: center; padding-top: 12px;">
<form action="servlet1" method="get">
名字:<input type="text" name="username" value="maxsu"/><input type="submit"
value="提交" />
</form>
</div>
</body>
</html>
文件:FirstServlet.java -
package com.yiibai;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* Servlet implementation class FirstServlet
*/
public class FirstServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
try {
PrintWriter out = response.getWriter();
String username = request.getParameter("username");
out.print("你好, " + username);
HttpSession session = request.getSession();
session.setAttribute("username", username);
session.setAttribute("age", "22");
out.print("<hr/><a href='servlet2'>在第二個(gè)Servlet訪問(wèn)Session屬性值</a>");
out.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
文件:SecondServlet.java -
package com.yiibai;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SecondServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
try {
PrintWriter out = response.getWriter();
HttpSession session = request.getSession(false);
String n = (String) session.getAttribute("username");
String age = (String) session.getAttribute("age");
out.print("您好, " + n + " !<br/> ");
out.print("你的年齡是: " + age + " 歲 ");
out.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
文件:web.xml -
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID" version="3.1">
<display-name>HttpSession</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>serv1</servlet-name>
<servlet-class>com.yiibai.FirstServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>serv1</servlet-name>
<url-pattern>/servlet1</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>s2</servlet-name>
<servlet-class>com.yiibai.SecondServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>s2</servlet-name>
<url-pattern>/servlet2</url-pattern>
</servlet-mapping>
</web-app>
在編寫(xiě)上面代碼后,部署此Web應(yīng)用程序(在項(xiàng)目名稱上點(diǎn)擊右鍵->”Run On Server…”),打開(kāi)瀏覽器訪問(wèn)URL: http://localhost:8080/HttpSession/ ,如果沒(méi)有錯(cuò)誤,應(yīng)該會(huì)看到以下結(jié)果 -
在上面輸入框中輸入:maxsu
,提交應(yīng)該會(huì)看到以下結(jié)果 -
注意:此時(shí)
FirstServlet
中HttpSession
的對(duì)象調(diào)用了setAttribute()
方法,設(shè)置了兩個(gè)屬性:username
和age
的值。
點(diǎn)擊上面的“在第二個(gè)Servlet訪問(wèn)Session
屬性值”鏈接,可以看到讀取Session
屬性的結(jié)果如下 -