messageleasehelper.java

实现了Jms的服务器源码,支持多种适配器,DB,FTP,支持多种数据库

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 * Copyright 2000-2003 (C) Exoffice Technologies Inc. All Rights Reserved.
 */

package org.exolab.jms.messagemgr;


import java.sql.Connection;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Vector;

import javax.jms.JMSException;
import javax.jms.Message;
import javax.transaction.TransactionManager;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.exolab.jms.lease.BaseLease;
import org.exolab.jms.lease.LeaseEventListenerIfc;
import org.exolab.jms.lease.LeaseManager;
import org.exolab.jms.lease.MessageLease;
import org.exolab.jms.message.MessageHandle;
import org.exolab.jms.message.MessageImpl;
import org.exolab.jms.persistence.DatabaseService;
import org.exolab.jms.persistence.PersistenceException;
import org.exolab.jms.persistence.SQLHelper;


/**
 * This is a helper class for registering leases for messages with
 * LeaseManager. The lease is based on the JMSExpiration property of the
 * message. <br>
 * When the lease expires, the listener's onLeaseExpired() method is invoked
 * with a MessageHandle object passed as the argument. <br>
 * If JMSExpiration is 0, the message never expires. <br>
 *
 * @version     $Revision: 1.16 $ $Date: 2003/08/17 01:32:24 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 * @see         MessageHandle
 * @see         LeaseManager
 * @see         LeaseEventListenerIfc
 */
public class MessageLeaseHelper implements LeaseEventListenerIfc {

    /**
     * The listener to notify when a lease expires
     */
    private LeaseEventListenerIfc _listener;

    /**
     * A map of MessageId -> MessageLease objects, representing
     * the active leases
     */
    private HashMap _leases = new HashMap();

    /**
     * A reference to the LeaseManager
     */
    private LeaseManager _leaseMgr;

    /**
     * The logger
     */
    private static final Log _log =
        LogFactory.getLog(MessageLeaseHelper.class);


    /**
     * Construct a helper for the specified destination cache.
     *
     * @param listener the object to notify when a lease expires
     * @throws PersistenceException if the destination is administered
     * and the set of non-expired messages cannot be determined
     */
    public MessageLeaseHelper(DestinationCache listener)
        throws PersistenceException {
        _listener = listener;
        _leaseMgr = LeaseManager.instance();

        Connection connection = null;

        try {
            connection = DatabaseService.getConnection();

            // initialise with the specified connection
            init(listener, connection);

            // commit the transactions
            connection.commit();
        } catch (PersistenceException exception) {
            SQLHelper.rollback(connection);
            throw exception;
        } catch (SQLException exception) {
            SQLHelper.rollback(connection);
            throw new PersistenceException(exception);
        } finally {
            SQLHelper.close(connection);
        }
    }

    /**
     * Construct a helper for the specified destination cache.
     * <p>
     * This method is only called during cache init time and is used to
     * retrieve persistent messages with leases.
     *
     * @param connection the connection to use to retrieve persistent messages
     * with leases
     * @param listener the object to notify when a lease expires
     * @throws PersistenceException if the destination is administered
     * and the set of non-expired messages cannot be determined
     */
    public MessageLeaseHelper(Connection connection, DestinationCache listener)
        throws PersistenceException {
        _listener = listener;
        _leaseMgr = LeaseManager.instance();

        init(listener, connection);
    }

    /**
     * Add a lease for message to notify listener when message expires.
     * The lease uses JMSExpiration property of the message. If this
     * is unset or 0, then no lease is registered. If non-zero, a
     * MessageHandle object is registered with LeaseManager, and
     * the listener will be notified with this object when the lease expires.
     *
     * @param message the message to add a lease for
     */
    public void addLease(MessageImpl message) {
        synchronized (_leases) {
            // ensure that a lease for this message does not already exist
            if (!_leases.containsKey(message.getMessageId())) {
                try {
                    long expiry = message.getJMSExpiration();
                    if (expiry > 0) {
                        // create an associated message handle and use it to
                        // create a
                        // lease for the message
                        MessageHandle handle =
                            MessageHandleFactory.getHandle(message);
                        long duration = expiry - System.currentTimeMillis();
                        MessageLease lease = _leaseMgr.createMessageLease(
                            handle, (duration <= 0 ? 1 : duration), this);
                        _leases.put(handle.getMessageId(), lease);
                    }
                } catch (JMSException exception) {
                    _log.error("Failed to create lease", exception);
                }
            }
        }
    }

    /**
     * Add a lease for the handle to notify listener when message expires.
     * The lease uses JMSExpiration property of the message. If this
     * is unset or 0, then no lease is registered. If non-zero, a
     * MessageHandle object is registered with LeaseManager, and
     * the listener will be notified with this object when the lease expires.
     *
     * @param handle message handle to add
     */
    public void addLease(MessageHandle handle) {
        synchronized (_leases) {
            // ensure that a lease for this message does not already exist.
            if (!_leases.containsKey(handle.getMessageId())) {
                long expiry = handle.getExpiryTime();
                if (expiry != 0) {
                    long duration = expiry - System.currentTimeMillis();
                    MessageLease lease = _leaseMgr.createMessageLease(
                        handle, (duration <= 0 ? 1 : duration), this);
                    _leases.put(handle.getMessageId(), lease);
                }
            }
        }
    }

    /**
     * Remove a lease for a message
     *
     * @param message the message to remove the lease for
     */
    public void removeLease(MessageImpl message) {
        try {
            MessageHandle handle = MessageHandleFactory.getHandle(message);
            if (handle != null) {
                synchronized (_leases) {
                    _leases.remove(handle.getMessageId());
                }
            }
        } catch (JMSException exception) {
            _log.error("Failed to remove lease", exception);
        }
    }

    /**
     * Clears all leases
     */
    public void clear() {
        Object[] leases = null;
        synchronized (_leases) {
            leases = _leases.values().toArray();
            _leases.clear();
        }

        for (int i = 0; i < leases.length; ++i) {
            BaseLease lease = (BaseLease) leases[i];
            _leaseMgr.removeLease(lease);
        }
    }

    /**
     * Invoked when a lease has expired.
     * <br>
     * It removes the local lease, and notifies the listener.
     *
     * @param       handle              An instance of MessageHandle
     */
    public void onLeaseExpired(Object handle) {
        synchronized (_leases) {
            _leases.remove(((MessageHandle) handle).getMessageId());
        }

        _listener.onLeaseExpired(handle);
    }

    /**
     * This method is used for all common initialization code. It basically
     * retrieves all non-expired messages and places them in the memory
     *
     * @param listener the cache listening for expired leases.
     * @param connection the persistent connection to use
     * @throws PersistenceException if the destination is administered
     * and the set of non-expired messages cannot be determined
     */
    protected void init(DestinationCache listener, Connection connection)
        throws PersistenceException {

        // if the destination is administered then retrieve a list of
        // nonexpired messages for this destination and add them to the
        // lease manager
        if (DatabaseService.getAdapter().checkDestination(
            connection, listener.getDestinationByName())) {
            Vector handles =
                DatabaseService.getAdapter().getNonExpiredMessages(
                    connection, listener.getDestination());
            if (handles != null) {
                Enumeration iter = handles.elements();
                while (iter.hasMoreElements()) {
                    PersistentMessageHandle handle =
                        (PersistentMessageHandle) iter.nextElement();
                    addLease(handle);
                }
            }
        }
    }

} //-- MessageLeaseHelper