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Hibernate ThreadLocal

2018年04月25日 ⁄ 综合 ⁄ 共 1502字 ⁄ 字号 评论关闭

Hibernate有很多值得学习的地方,这里我们主要介绍Hibernate ThreadLocal,包括介绍Hibernate官方开发手册标准示例等方面。

Hibernate ThreadLocal

它会为每个线程维护一个私有的变量空间。实际上, 其实现原理是在JVM 中维护一个Map,这个Map的key 就是当前的线程对象,而value则是 线程通过Hibernate ThreadLocal.set方法保存的对象实例。当线程调用Hibernate ThreadLocal.get方法时, Hibernate ThreadLocal会根据当前线程对象的引用,取出Map中对应的对象返回。

这样,Hibernate ThreadLocal通过以各个线程对象的引用作为区分,从而将不同线程的变量隔离开来。

Hibernate官方开发手册标准示例:

    public class HibernateUtil {   
    private static SessionFactory sessionFactory;  
    static {   
    try {   
    // Create the SessionFactory sessionFactory = new Configuration().
    configure().buildSessionFactory();  
    }   
    catch (HibernateException ex) {   
    throw new RuntimeException( "Configuration problem: " + ex.getMessage(), ex );  
    }   
    }   
    public static final ThreadLocal session = new ThreadLocal();  
    public static Session currentSession() throws HibernateException {   
    Session s = (Session) session.get();  
    // Open a new Session, if this Thread has none yet if (s == null) {   
    s = sessionFactory.openSession();  
    session.set(s);  
    }   
    return s;  
    }   
    public static void closeSession() throws HibernateException {   
    Session s = (Session) session.get();  
    session.set(null);  
    if (s != null) s.close();  
    }   
    } 

通过filter实现session的重用:

    public class PersistenceFilter implements Filter {   
    protected static ThreadLocal hibernateHolder = new ThreadLocal();  
    public void doFilter(ServletRequest request, 
    ServletResponse response, FilterChain chain) 
    throws IOException,ServletException {   
    hibernateHolder.set(getSession());  
    try {   
    ……   
    chain.doFilter(request, response);  
    ……   
    }   
    finally {   
    Session sess = (Session)hibernateHolder.get();  
    if (sess != null) { hibernateHolder.set(null);  
    try { sess.close(); } catch (HibernateException ex) {   
    throw new ServletException(ex);  
    }   
    }   
    }   
    }   
    ……  
    } 

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