seedgenerator.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

/**
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "Exolab" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Exoffice Technologies.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "Exolab"
 *    nor may "Exolab" appear in their names without prior written
 *    permission of Exoffice Technologies. Exolab is a registered
 *    trademark of Exoffice Technologies.
 *
 * 5. Due credit should be given to the Exolab Project
 *    (http://www.exolab.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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 * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 2000-2004 (C) Exoffice Technologies Inc. All Rights Reserved.
 */

package org.exolab.jms.persistence;


import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import javax.sql.DataSource;


/**
 * This class generates seeds
 *
 * @version     $Revision: 1.6 $ $Date: 2004/01/11 02:35:45 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 *
 **/
public class SeedGenerator {

    /**
     * Caches the singleton instance of this class
     */
    private static SeedGenerator _instance;

    /**
     * Monitor used to synchronize the initialization of the
     * singleton class instance
     */
    private static final Object _block = new Object();


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

    /**
     * Initialise the seed generator
     *
     * @return      SeedGenerator       the singleton instance
     */
    public static SeedGenerator initialise() {
        if (_instance == null) {
            synchronized (_block) {
                if (_instance == null) {
                    _instance = new SeedGenerator();
                }
            }
        }

        return _instance;
    }

    /**
     * Return the next seed value for the given name
     *
     * @param connection - the connection used
     * @param seed - the name of the seed
     * @return long - the next seed value
     * @exception PersistenceException - if the seed cannot be retrieved
     */
    public synchronized long next(Connection connection, String name)
        throws PersistenceException {

        PreparedStatement select = null;
        PreparedStatement update = null;
        PreparedStatement insert = null;
        ResultSet result = null;
        long value = 0;

        boolean successful = false;
        try {
            select = connection.prepareStatement(
                "select * from seeds where name=?");
            select.setString(1, name);

            result = select.executeQuery();
            if (result.next()) {
                value = result.getLong("seed");
                value++;
                update = connection.prepareStatement(
                    "update seeds set seed=? where name=?");
                update.setLong(1, value);
                update.setString(2, name);
                update.executeUpdate();
            } else {
                value = 1;
                insert = connection.prepareStatement(
                    "insert into seeds values (?,?)");
                insert.setString(1, name);
                insert.setLong(2, value);
                insert.executeUpdate();
            }
        } catch (Exception exception) {
            throw new PersistenceException("next " + exception.getMessage());
        } finally {
            SQLHelper.close(select);
            SQLHelper.close(update);
            SQLHelper.close(insert);
            SQLHelper.close(result);
        }

        return value;
    }

    /**
     * Remove all seeds.
     *
     * @param connection - the connection to use
     * @exception PersistenceException - is thrown if the request does not
     *                                   complete
     */
    public void removeAll(Connection connection)
        throws PersistenceException {

        PreparedStatement delete = null;
        try {
            delete = connection.prepareStatement("delete from seeds");
            delete.executeUpdate();
        } catch (Exception error) {
            throw new PersistenceException("Failed in removeAll with " +
                error.toString());
        } finally {
            SQLHelper.close(delete);
        }
    }

    /**
     * Issue a close, which in this case invalidates the singleton
     * TODO: do we really need this
     */
    public void close() {
        _instance = null;
    }

    /**
     * Constructor
     *
     * @param       connectionPool      the connection pool
     * @param       manager             the transaction manager
     */
    protected SeedGenerator() {
    }
}