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hibernate3學習筆記(六) Session管理

編輯：關於JAVA

請注意，在hibernate中SessionFactory是被設計成線程安全(Thread-safe)的,遺憾的是，Session卻線程不安全。

這就意味著:有可能多個線程共享並操作同一個Session從而很容易使數據混亂。

解決的辦法如下：（其實hibernate的文檔中早已經提過了）

新建HibernateUtil類：

1.import org.apache.commons.logging.Log;
2.import org.apache.commons.logging.LogFactory;
3.import org.hibernate.*;
4.import org.hibernate.cfg.*;
5.
6.public class HibernateUtil {
7.    private static Log log = LogFactory.getLog(HibernateUtil.class);
8.    private static final SessionFactory sessionFactory;
9.
10.    static {
11.        try {
12.            // Create the SessionFactory
13.            sessionFactory = new Configuration().configure()
14.                                                .buildSessionFactory();
15.        } catch (Throwable ex) {
16.            // Make sure you log the exception, as it might be swallowed
17.            log.error("Initial SessionFactory creation failed.", ex);
18.            throw new ExceptionInInitializerError(ex);
19.        }
20.    }
21.
22.    public static final ThreadLocal session = new ThreadLocal();
23.
24.    public static Session currentSession() {
25.        Session s = (Session) session.get();
26.
27.        // Open a new Session, if this Thread has none yet
28.        if (s == null) {
29.            s = sessionFactory.openSession();
30.            session.set(s);
31.        }
32.
33.        return s;
34.    }
35.
36.    public static void closeSession() {
37.        Session s = (Session) session.get();
38.
39.        if (s != null) {
40.            s.close();
41.        }
42.
43.        session.set(null);
44.    }
45.}

這樣，在程序中可這樣調用：

1.Session session = HibernateUtil.currentSession();
2.User user = (User) session.load(User.class, new Integer(1));
3.System.out.println(user.getName());
4.HibernateUtil.closeSession();

在web應用中，可以借由Filter來進行session管理。在需要session的時候開啟session，在request結束之後關閉session。

HibernateSessionUtil.java

1.import java.io.Serializable;
2.
3.import net.sf.hibernate.HibernateException;
4.import net.sf.hibernate.Session;
5.import net.sf.hibernate.SessionFactory;
6.import net.sf.hibernate.Transaction;
7.
8.public class HibernateSessionUtil implements Serializable
9.{
10.    public static final ThreadLocal tLocalsess = new ThreadLocal();
11.
12.    public static final ThreadLocal tLocaltx = new ThreadLocal();
13.
14.    /*
15.     * getting the thread-safe session for using
16.     */17.    public static Session currentSession(){
18.        Session session = (Session) tLocalsess.get();
19.
20.        //open a new one, if none can be found.
21.        try{
22.            if (session == null){
23.                session = openSession();
24.                tLocalsess.set(session);
25.            }
26.        }catch (HibernateException e){
27.            throw new InfrastructureException(e);
28.        }
29.        return session;
30.    }
31.
32.    /*
33.     * closing the thread-safe session
34.     */
35.    public static void closeSession(){
36.
37.        Session session = (Session) tLocalsess.get();
38.        tLocalsess.set(null);
39.        try{
40.            if (session != null && session.isOpen()){
41.                session.close();
42.            }
43.
44.        }catch (HibernateException e){
45.            throw new InfrastructureException(e);
46.        }
47.    }
48.
49.    /*
50.     * begin the transaction
51.     */
52.    public static void beginTransaction(){
53.        Transaction tx = (Transaction) tLocaltx.get();
54.        try{
55.            if (tx == null){
56.                tx = currentSession().beginTransaction();
57.                tLocaltx.set(tx);
58.            }
59.        }catch (HibernateException e){
60.            throw new InfrastructureException(e);
61.        }
62.    }
63.
64.    /*
65.     * close the transaction
66.     */
67.    public static void commitTransaction(){
68.        Transaction tx = (Transaction) tLocaltx.get();
69.        try{
70.            if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack())
71.                tx.commit();
72.            tLocaltx.set(null);
73.        }catch (HibernateException e){
74.            throw new InfrastructureException(e);
75.        }
76.    }
77.
78.    /*
79.     * for rollbacking
80.     */
81.    public static void rollbackTransaction(){
82.        Transaction tx = (Transaction) tLocaltx.get();
83.        try{
84.            tLocaltx.set(null);
85.            if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()){
86.                tx.rollback();
87.            }
88.        }catch (HibernateException e){
89.            throw new InfrastructureException(e);
90.        }
91.    }
92.
93.    private static Session openSession() throws HibernateException{
94.        return getSessionFactory().openSession();
95.    }
96.
97.    private static SessionFactory getSessionFactory() throws HibernateException{
98.        return SingletonSessionFactory.getInstance();
99.    }
100.}

filter中則：

1.public class HibernateSessionCloser implements Filter{
2.
3.    protected FilterConfig filterConfig = null;
4.
5.    public void init(FilterConfig filterConfig)throws ServletException{
6.    this.filterConfig = filterConfig;
7.    }
8.    
9.    public void destroy(){
10.        this.filterConfig = null;
11.    }    
12.
13.    public void doFilter(ServletRequest request, ServletResponse response,
14.                         FilterChain chain)
15.    throws IOException, ServletException {
16.        try{
17.            chain.doFilter(request, response);
18.        }
19.        finally{
20.            try{
21.                HibernateSessionUtil.commitTransaction();
22.            }catch (InfrastructureException e){
23.                HibernateSessionUtil.rollbackTransaction();
24.            }finally{
25.                HibernateSessionUtil.closeSession();
26.            }   
27.        }
28.
29.    }
30.}