Session
- 概念:服務器端會話技術,在一次對話的屢次請求間共享數據,將數據保存在服務器端的對象中。HttpSession
- 快速入門:
- 獲取Session對象
* HttpSession session=request.getSession();
- 使用HttpSession對象:
* Object getAttribute(String name)
* void setArrtibute(String name,Object value)
* void removeAttribute(String name)
- 原理
* Session的實現是依賴於Cookie的
- 細節
1. 當客戶端關閉後,服務器不關閉,兩次獲取的session是否爲同一個
- 默認狀況下,不是
- 若是須要相同,則能夠建立Cookie。鍵爲JSESSIONID,設置最大存活時間,讓cookie持久化保存
- Cookie c=new Cookie("JSESSIONID",session.getId());
- c.setMaxAge(60*60);
- response.addCookie(c);
2. 客戶端不關閉,服務器關閉後,兩次獲取的session是同一個嗎?
* 不是同一個,可是要確保數據不丟失
* session的鈍化
* 在服務器正常關閉以前,將session對象系列化到硬盤上
* session的活化
* 在服務器啓動後,將session文件轉化爲內存中的session對象便可
3. session的失效時間
1. 服務器關閉
2. session對象調用invalidate()
3. session默認失效時間 30分鐘
* 選擇性配置修改 <session-config><session-timeout>30</session-timeout></session-config>
- session的特色
1. session用於存儲一次會話的屢次請求的數據,存在服務器端
2. session能夠存儲任意類型,任意大小的數據
* session與cookie的區別
- session存儲數據在服務器端,Cookie在客戶端
- session沒有數據大小限制,Cookie有
- session數據安全,Cookie相對於不安全
Session使用
建立Session對象,存儲Session對象
package cn.itcast.session;
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;
import java.io.IOException;
@WebServlet("/SessionDemo1")
public class SessionDemo1 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//使用session共享數據
// 1.獲取session
HttpSession session=request.getSession();
// 2.存儲數據
session.setAttribute("msg","hello session");
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
}
獲取session
package cn.itcast.session;
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;
import java.io.IOException;
@WebServlet("/SessionDemo2")
public class SessionDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//使用session共享數據
// 1.獲取session
HttpSession session=request.getSession();
// 2.獲取數據
Object msg=session.getAttribute("msg");
System.out.println(msg);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
}
session的保存,是在服務器上
package cn.itcast.session;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
@WebServlet("/SessionDemo3")
public class SessionDemo3 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 1.獲取session
HttpSession session=request.getSession();
System.out.println(session);
//期待客戶端關閉後,session也能相同
Cookie c=new Cookie("JSESSIONID",session.getId());
c.setMaxAge(60*60);
response.addCookie(c);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
}