ThreadLocal实现每条线程都有属于自己的session实例

[java] view plain copy print ?

1. import org.hibernate.Session; 
2. import org.hibernate.SessionFactory; 
3. import org.hibernate.cfg.Configuration; 
4.  
5. public class SessionUtil { 
6.     private static SessionFactory factory; 
7.     private static ThreadLocal<Session> threadLocal = new ThreadLocal<Session>(); 
8.  
9.     // 获取SessionFactory 
10.     static {   // 静态初始化块，加载配置信息 
11.         Configuration cfg = new Configuration().configure();  // 读取hibernate.cfg.xml文件 
12.         factory = cfg.buildSessionFactory();  // 建立SessionFactory 
13.     } 
14.  
15.     public static Session getSession() { 
16.         Session session = threadLocal.get();  //获取当前线程下的session 
17.         if(session==null) { 
18.             System.out.println("session is null!"); 
19.             session = factory.openSession(); 
20.             threadLocal.set(session); 
21.         } 
22.         return session; 
23.     } 
24.     public static void closeSession() { 
25.         Session session = threadLocal.get(); 
26.         //如果session不为null，则关闭session，并清空ThreadLocal 
27.         if(session!=null) { 
28.             session.close(); 
29.             threadLocal.set(null); 
30.         } 
31.     } 
32.  
33. } 

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class SessionUtil {
    private static SessionFactory factory;
    private static ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();

    // 获取SessionFactory
    static {   // 静态初始化块，加载配置信息
        Configuration cfg = new Configuration().configure();  // 读取hibernate.cfg.xml文件
        factory = cfg.buildSessionFactory();  // 建立SessionFactory
    }

    public static Session getSession() {
        Session session = threadLocal.get();  //获取当前线程下的session
        if(session==null) {
            System.out.println("session is null!");
            session = factory.openSession();
            threadLocal.set(session);
        }
        return session;
    }
    public static void closeSession() {
        Session session = threadLocal.get();
        //如果session不为null，则关闭session，并清空ThreadLocal
        if(session!=null) {
            session.close();
            threadLocal.set(null);
        }
    }

}

接下来进行测试：

创建MyThread.java并继承Thread类

[java] view plain copy print ?

1. import org.hibernate.Session; 
2.  
3. public class MyThread extends Thread{ 
4.     @Override 
5.     public void run() { 
6.         Session session1 = SessionUtil.getSession(); 
7.         Session session2 = SessionUtil.getSession(); 
8.         Session session3 = SessionUtil.getSession(); 
9.         long threadId = this.getId(); //获取线程id 
10.         //输出hashCode，分辨是否是同一个session实例 
11.         System.out.println("线程" +threadId+ ":\n" + session1.hashCode() + "\n"  + session2.hashCode() + "\n" + session3.hashCode()); 
12.     } 
13. } 

import org.hibernate.Session;

public class MyThread extends Thread{
    @Override
    public void run() {
        Session session1 = SessionUtil.getSession();
        Session session2 = SessionUtil.getSession();
        Session session3 = SessionUtil.getSession();
        long threadId = this.getId(); //获取线程id
        //输出hashCode，分辨是否是同一个session实例
        System.out.println("线程" +threadId+ ":\n" + session1.hashCode() + "\n"  + session2.hashCode() + "\n" + session3.hashCode());
    }
}

运行结果：

为什么使用TreadLocal来实现？

当使用ThreadLocal维护变量时，ThreadLocal为每个使用该变量的线程提供独立的变量副本，所以每一个线程都可以独立地改变自己的副本，而不会影响其它线程所对应的副本。