Java中Session的详解

时间：2022-12-02 12:39:40

1.什么是session：

服务器会给每一个用户（浏览器）创建一个session对象

一个session独占一个浏览器，只要浏览器不关闭，这个session就一直存在

session称为会话控制，存储用户会话所需的属性和配置信息，这样，用户在应用程序的web页面跳转时，存储在session对象中的用户信息不会丢掷，而是在整个用户会话中一直保持下去

2.session的经典应用场景：

一个用户登陆后，访问该网站的其他网页时，一直处于登录状态

保存购物车信息等等

3.session中常用的方法

getId()：获取session的唯一标识

getServletContext()：代表整个web服务

getAttribute(String)：获取session的节点，比如你在其中一个Servlet中通过setAttribute(String,Object)配置了相关的session信息，然后通过另一个Servlet获取这个Servlet中的session信息，就要用到getAttribute(String)这个方法

setAttribute(String,Object)：设置session节点

removeAttribute(String)：一出一个session节点

isNew()：判断一个session是否是一个新的session

invalidate()：注销session的

4.举例

例1：创建一个session并获取到session的ID，判断这个session是否是新的session

步骤1：新建一个maven项目，使用webapp模板

步骤2：在Java文件夹下创建一个com.xiaoma.servlet.SessionDemo01的类，编写servlet类文件

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
package com.xiaoma.servlet;
import com.xiaoma.pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import javax.servlet.http.HttpSession;
 import java.io.IOException;
 public class SessionDemo01 extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         //解决中文乱码
         resp.setHeader("content-type","text/html;charset=UTF-8");
         //得到session
         HttpSession session = req.getSession();
         //通过setAttribute方法向Session中存放信息
         session.setAttribute("name","小马");
         //获取session相关信息，包括id，是否是新的session等
         String sessionId = session.getId();
         if(session.isNew()) {
             resp.getWriter().write("创建Session成功，ID为：" + sessionId);
         }else{
             resp.getWriter().write("Session已经存在了，ID为：" + sessionId);
         }
     }
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

步骤3：配置XML文件

?
1
2
3
4
5
6
7
8
<servlet>
         <servlet-name>SessionDemo01</servlet-name>
         <servlet-class>com.xiaoma.servlet.SessionDemo01</servlet-class>
     </servlet>
     <servlet-mapping>
         <servlet-name>SessionDemo01</servlet-name>
         <url-pattern>/s1</url-pattern>
     </servlet-mapping>

例2：从一个servlet中读取另一个servlet中的session信息

步骤1：在Java文件夹下创建一个com.xiaoma.servlet.SessionDemo01的类，编写servlet类文件

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
package com.xiaoma.servlet;
 import com.xiaoma.pojo.Person;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决中文乱码
        resp.setHeader("content-type","text/html;charset=UTF-8");
        //得到session
        HttpSession session = req.getSession();
        //通过setAttribute方法向Session中存放信息
        session.setAttribute("name","小马");
        //获取session相关信息，包括id，是否是新的session等
        String sessionId = session.getId();
        if(session.isNew()) {
            resp.getWriter().write("创建Session成功，ID为：" + sessionId);
        }else{
            resp.getWriter().write("Session已经存在了，ID为：" + sessionId);
       }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

步骤2：在Java文件夹下创建一个com.xiaoma.servlet.SessionDemo02的类，编写另一个用来读取的servlet类，通过SessionDemo02来读取SessionDemo01中的session信息

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
package com.xiaoma.servlet;
 import com.xiaoma.pojo.Person;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 import java.io.IOException;
public class SessionDemo02 extends HttpServlet {
   @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决中文乱码
       resp.setHeader("content-type","text/html;charset=UTF-8");
        //得到session
        HttpSession session = req.getSession();
        String name=(String) session.getAttribute("name");
        resp.getWriter().write(name);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

步骤3：配置xml文件

?
1
2
3
4
5
6
7
8
<servlet>
    <servlet-name>SessionDemo02</servlet-name>
   <servlet-class>com.xiaoma.servlet.SessionDemo02</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>SessionDemo02</servlet-name>
    <url-pattern>/s2</url-pattern>
</servlet-mapping>

例3：session中还可以存放对象信息

步骤1：在Java文件夹下创建一个com.xiaoma.pojo.Person的类，编写我们的实体类

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
package com.xiaoma.pojo;
 public class Person {
     private String name;
     private int age;
     public Person() {
     }
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
     public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Person{" +
               "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

步骤2：在Java文件夹下创建一个com.xiaoma.servlet.SessionDemo01的类，编写servlet类文件

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
package com.xiaoma.servlet;
 import com.xiaoma.pojo.Person;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
import java.io.IOException;
public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //解决中文乱码
        resp.setHeader("content-type","text/html;charset=UTF-8");
       //得到session
        HttpSession session = req.getSession();
        //通过setAttribute方法向Session中存放信息
        session.setAttribute("name",new Person("小马",18));
        //获取session相关信息，包括id，是否是新的session等
        String sessionId = session.getId();
        if(session.isNew()) {
            resp.getWriter().write("创建Session成功，ID为：" + sessionId);
        }else{
            resp.getWriter().write("Session已经存在了，ID为：" + sessionId);
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

步骤3：在Java文件夹下创建一个com.xiaoma.servlet.SessionDemo02的类，编写另一个servlet类文件，用来读取SessionDemo01中的Session对象信息

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
package com.xiaoma.servlet;
  import com.xiaoma.pojo.Person;
  import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import javax.servlet.http.HttpSession;
import java.io.IOException;
 public class SessionDemo02 extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         //获取session中的Person对象
         //解决中文乱码
         resp.setHeader("content-type","text/html;charset=UTF-8");
         //得到session
         HttpSession session = req.getSession();
         Person person=(Person) session.getAttribute("name");
         resp.getWriter().write(person.toString());
     }
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         super.doPost(req, resp);
     }
 }

步骤4：编写xml文件，与上同理

例4：注销session（注销session有两种方式，一种是通过removeAttribute(String)方法，另一种是通过xml配置文件）

第一种，通过removeAttribute(String)方法，这种方式是使session手动过期

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
  package com.xiaoma.servlet;
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import javax.servlet.http.HttpSession;
 import java.io.IOException;
 public class SessionDemo03 extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         //得到session
         HttpSession session = req.getSession();
         //手动注销session
        session.removeAttribute("name");
         session.invalidate();
     }
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         super.doPost(req, resp);
     }
}

第二种，通过xml文件的方法，这种方式是时session自动过期

?
1
2
3
4
5
<!--设置session的存活时间-->
<session-config>
    <!--以分钟为单位-->
    <session-timeout>1</session-timeout>
</session-config>

5.session与cookie的区别

　　·（1）cookie是吧用户的数据写给浏览器，浏览器保存(可以保存多个)

　　·（2）session是把用户的数据写给用户独占的session中，服务器保存（保存重要信息，避免浪费服务器资源）

　　·（3）session是由服务器创建的

原文链接：https://www.cnblogs.com/XiaoMaGuai/p/15374013.html

标签：

相关文章