public void testBeginTransaction() throws TransactionException,SQLException {
        Transaction tx = null;
        try {
            tx = ConnectionManager.beginTransaction();
            
            assertEquals("aaa",findProduct16());
            
            updateProduct16();
            assertEquals("萝卜",findProduct16());
            
            assertEquals("Alice Mutton",findProduct17());
            updateProduct17();
            //assertEquals("白菜",findProduct17());
            
            tx.commit();
            assertTrue(tx.wasCommitted());
            /*
            tx.commit();
            assertTrue(tx.wasCommitted());
            assertEquals("萝卜",findProduct16());
            */
            
            /*
            tx.rollback();
            assertTrue(tx.wasRolledBack());
            assertEquals("aaa",findProduct16());
            assertEquals("Alice Mutton",findProduct17());
            */
            
        } catch (TransactionException e) {
            tx.rollback();
            assertTrue(tx.wasRolledBack());
            throw e;
        } catch (SQLException e) {
            tx.rollback();
            assertTrue(tx.wasRolledBack());
            //throw new TransactionException(e);
        }
        
        assertTrue(ConnectionManager.currentConnection().getAutoCommit());
    }

public class ConnectionManager {
    private static final ThreadLocal connection = new ThreadLocal();
    private static ConnectionFactory factory;
    private static boolean initialized = false;
    private static final Log log = LogFactory.getLog(ConnectionManager.class);

    private ConnectionManager() {
        super();
    }

    private synchronized static void initialize() {
        try {
            factory = new Configuration().configure().buildConnectionFactory();
        } catch (ConfigureException e) {
            log.fatal(e);
        }
        log.info("ConnectionManager initialize success");
        initialized = true;
    }

    public static Connection currentConnection() throws SQLException {
        if(!initialized) {
            initialize();
        }
        Connection conn = (Connection)connection.get();
        if(conn == null) {
            conn = factory.openConnection();
            connection.set(conn);
        }
        return conn;
    }

    public static void closeConnection() throws SQLException {
        Connection conn = (Connection)connection.get();
        connection.set(null);
        if(conn != null) {
            conn.close();
        }
    }

    public static Transaction beginTransaction() throws TransactionException{
        Connection conn = null;
        try {
            conn = currentConnection();
        } catch (SQLException e) {
            log.error("Can't get current connection with SQLException:",e);
            throw new TransactionException("Begin tracsaction fail with SQLException:", e);
        }
        
        return new TransactionFactory().beginTransaction(conn);
    }
}

在ThreadLocal类中有一个Map，用于存储每一个线程的变量的副本。