consumers.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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package org.exolab.jms.persistence;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Vector;

import javax.jms.JMSException;
import javax.sql.DataSource;

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

import org.exolab.jms.client.JmsDestination;
import org.exolab.jms.client.JmsTopic;


/**
 * This class provides persistency for ConsumerState objects
 * in an RDBMS database
 *
 * @version     $Revision: 1.9 $ $Date: 2003/08/07 13:33:06 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 * @see         org.exolab.jms.persistence.ConsumerState
 * @see         org.exolab.jms.persistence.RDBMSAdapter
 */
class Consumers {

    /**
     * A cache for all durable consumers
     */
    private HashMap _consumers;

    /**
     * A refernce to the singleton instance of this class
     */
    private static Consumers _instance;

    /**
     * Monitor used to synchronize access to the initialization of
     * the singleton
     */
    private static final Boolean block = new Boolean(true);

    /**
     * The name of the column that uniquely identifies the consumer
     */
    private static final String CONSUMER_ID_SEED = "consumerId";

    /**
     * The name of the table that maintains a list of message handles
     * per consumer
     */
    private static final String CONSUMER_MESSAGE = "message_handles";

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


    /**
     * Returns the singleton instance.
     *
     * Note that initialise() must have been invoked first for this
     * to return a valid instance.
     *
     * @return      Consumers           the singleton instance
     */
    public static Consumers instance() {
        return _instance;
    }

    /**
     * Initialise the singleton instance
     *
     * @param Connection - the connection to use
     * @return Consumers -  singleton instance
     * @throws PersistenceException - if the call cannot complete
     */
    public static Consumers initialise(Connection connection)
        throws PersistenceException {

        if (_instance == null) {
            synchronized (block) {
                if (_instance == null) {
                    _instance = new Consumers();
                    _instance.load(connection);
                }
            }
        }
        return _instance;
    }

    /**
     * Add a new durable consumer to the database if it does not already
     * exist. A durable consumer is specified by a destination name and
     * a consumer name.
     * <p>
     * The destination must resolve to a valid JmsDestination object
     *
     * @param connection - the database connection to use
     * @param destination - the name of the destination
     * @param consumer - the name of the consumer
     * @throws PersistenceException - if the consumer cannot be added
     */
    public synchronized void add(Connection connection, String dest,
                                 String consumer)
        throws PersistenceException {

        JmsDestination destination = null;
        Destinations singleton = Destinations.instance();
        long destinationId = 0;

        synchronized (singleton) {
            destination = singleton.get(dest);
            if (destination == null) {
                raise("add", consumer, dest, "destination is invalid");
            }
            destinationId = singleton.getId(dest);
        }

        // check that for a topic the consumer name is not the same as the
        // destination name
        if ((destination instanceof JmsTopic) &&
            (consumer.equals(dest))) {
            raise("add", consumer, dest,
                "The consumer name and destination name cannot be the same");
        }

        // get the next id from the seed table
        long consumerId = SeedGenerator.instance().next(connection,
            CONSUMER_ID_SEED);

        PreparedStatement insert = null;
        try {
            insert = connection.prepareStatement(
                "insert into consumers values (?,?,?,?)");

            long created = (new Date()).getTime();
            insert.setString(1, consumer);
            insert.setLong(2, destinationId);
            insert.setLong(3, consumerId);
            insert.setLong(4, created);
            insert.executeUpdate();

            Consumer map = new Consumer(consumer, consumerId,
                destinationId, created);

            // check to see if the durable consumer already exists. If it
            // does then do not add it but signal and error
            if (!_consumers.containsKey(consumer)) {
                _consumers.put(consumer, map);
            } else {
                _log.error("Durable consumer with name " + consumer
                    + " already exists.");
            }
        } catch (Exception exception) {
            throw new PersistenceException(
                "Failed to add consumer, destination=" + dest +
                ", name=" + consumer, exception);
        } finally {
            SQLHelper.close(insert);
        }
    }

    /**
     * Remove a consumer from the database. If the destination is of
     * type queue then the destination name and the consumer name are
     * identical.
     *
     * @param connection - the connection to use
     * @param name - the consumer name
     * @throws PersistenceException - if the consumer cannot be removed
     */
    public synchronized void remove(Connection connection, String name)
        throws PersistenceException {

        PreparedStatement delete = null;

        // locate the consumer
        Consumer map = (Consumer) _consumers.get(name);
        if (map == null) {
            raise("remove", name, "consumer does not exist");
        }

        try {
            delete = connection.prepareStatement(
                "delete from consumers where name=?");
            delete.setString(1, name);
            delete.executeUpdate();

            // now delete all the corresponding handles in the consumer
            // message table
            remove(CONSUMER_MESSAGE, map.consumerId, connection);

            // remove the consumer from the local cache
            _consumers.remove(name);
        } catch (SQLException exception) {
            throw new PersistenceException(
                "Failed to remove consumer=" + name, exception);
        } finally {
            SQLHelper.close(delete);
        }