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。
具体实现如下:
创建类 SessionUtil.java
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>();
// 静态初始化块,加载配置信息,获取SessionFactory
static {
// 读取hibernate.cfg.xml文件
Configuration cfg = new Configuration().configure();
// 建立SessionFactory
factory = cfg.buildSessionFactory();
}
public static Session getSession() {
//获取当前线程下的session
Session session = threadLocal.get();
//如果session为null,则从SessionFactory中获取一个session放入ThreadLocal
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:
首先创建MyThread.java并继承Thread类
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();
//获取线程id
long threadId = this.getId();
//输出session的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());
}
}
创建Test.java
public class Test {
public static void main(String[] args) {
MyThread thread1 = new MyThread();
MyThread thread2 = new MyThread();
MyThread thread3 = new MyThread();
//启动线程
thread1.start();
thread2.start();
thread3.start();
}
}