ThreadLoca的l类详解

public class HibernateUtil {
    private static Log log = LogFactory.getLog(HibernateUtil.class);
    private static final SessionFactory sessionFactory;     //定义SessionFactory
 
    static { 
        try { 
            // 通过默认配置文件hibernate.cfg.xml创建SessionFactory 
            sessionFactory = new Configuration().configure().buildSessionFactory(); 
        } catch (Throwable ex) { 
            log.error("初始化SessionFactory失败！", ex); 
            throw new ExceptionInInitializerError(ex); 
        } 
    }

    //创建线程局部变量session，用来保存Hibernate的Session 
    public static final ThreadLocal session = new ThreadLocal();
 
    /** 
     * 获取当前线程中的Session 
     * @return Session 
     * @throws HibernateException 
     */ 
    public static Session currentSession() throws HibernateException { 
        Session s = (Session) session.get(); 
        // 如果Session还没有打开，则新开一个Session 
        if (s == null) { 
            s = sessionFactory.openSession(); 
            session.set(s);         //将新开的Session保存到线程局部变量中 
        } 
        return s; 
    }
 
    public static void closeSession() throws HibernateException { 
        //获取线程局部变量，并强制转换为Session类型 
        Session s = (Session) session.get(); 
        session.set(null); 
        if (s != null) 
            s.close(); 
    } 
}

/** 
 * Created by IntelliJ IDEA. 
 * User: leizhimin 
 * Date: 2007-11-23 
 * Time: 10:45:02 
 * 学生 
 */ 
public class Student { 
    private int age = 0;   //年龄
 
    public int getAge() { 
        return this.age; 
    }
 
    public void setAge(int age) { 
        this.age = age; 
    } 
}
 
/** 
 * Created by IntelliJ IDEA. 
 * User: leizhimin 
 * Date: 2007-11-23 
 * Time: 10:53:33 
 * 多线程下测试程序 
 */ 
public class ThreadLocalDemo implements Runnable { 
    //创建线程局部变量studentLocal，在后面你会发现用来保存Student对象 
    private final static ThreadLocal studentLocal = new ThreadLocal();
 
    public static void main(String[] agrs) { 
        ThreadLocalDemo td = new ThreadLocalDemo(); 
        Thread t1 = new Thread(td, "a"); 
        Thread t2 = new Thread(td, "b"); 
        t1.start(); 
        t2.start(); 
    }
 
    public void run() { 
        accessStudent(); 
    }
 
    /** 
     * 示例业务方法，用来测试 
     */ 
    public void accessStudent() { 
        //获取当前线程的名字 
        String currentThreadName = Thread.currentThread().getName(); 
        System.out.println(currentThreadName + " is running!");
        //产生一个随机数并打印 
        Random random = new Random(); 
        int age = random.nextInt(100); 
        System.out.println("thread " + currentThreadName + " set age to:" + age);
        //获取一个Student对象，并将随机数年龄插入到对象属性中 
        Student student = getStudent(); 
        student.setAge(age); 
        System.out.println("thread " + currentThreadName + " first read age is:" + student.getAge()); 
        try { 
            Thread.sleep(500); 
        } 
        catch (InterruptedException ex) { 
            ex.printStackTrace(); 
        } 
        System.out.println("thread " + currentThreadName + " second read age is:" + student.getAge()); 
    }
 
    protected Student getStudent() { 
        //获取本地线程变量并强制转换为Student类型 
        Student student = (Student) studentLocal.get(); 
        //线程首次执行此方法的时候，studentLocal.get()肯定为null 
        if (student == null) { 
            //创建一个Student对象，并保存到本地线程变量studentLocal中 
            student = new Student(); 
            studentLocal.set(student); 
        } 
        return student; 
    } 
}