Metacat

/**

 *  '$RCSfile$'

 *    Purpose: A class represent a DBConnection pool. Another user can use the

 *    object to initial a connection pool, get db connection or return it. 

 *  Copyright: 2000 Regents of the University of California and the

 *             National Center for Ecological Analysis and Synthesis

 *    Authors: Jing Tao

 *    Release: @release@

 *

 *   '$Author$'

 *     '$Date$'

 * '$Revision$'

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

package edu.ucsb.nceas.metacat;

import java.io.*;

import java.util.Vector;

import java.util.zip.*;

import java.net.URL;

import java.net.MalformedURLException;

import java.sql.*;

import java.util.Stack;

import java.util.Hashtable;

import java.util.Enumeration;

/** 

 * A class represent a DBConnection pool. Another user can use the

 * object to initial a connection pool, get db connection or return it.

 * This a singleton class, this means only one instance of this class could

 * be in the program at one time. 

 */

public class DBConnectionPool

{

  private String DBDriver;

  private String DBConnectedJDBC;

  private String userName;

  private String passWord;

  private int currentConnectionNumber;

  //static attributes

  private static DBConnectionPool instance;

  private static Vector connectionPool;

  final static int maximumConnectionNumber=

                  Integer.parseInt(MetaCatUtil.getOption("maximumConnections"));

  final static int initialConnectionNumber=

                  Integer.parseInt(MetaCatUtil.getOption("initialConnections"));

  /**

   * Returns the single instance, creating one if it's the

   * first time this method is called.

   */

  static synchronized public DBConnectionPool getInstance()

                                 throws SQLException, ClassNotFoundException 

  {

    if (instance == null) 

    {

      instance = new DBConnectionPool();

    }

    return instance;

  }//getInstance

  /**

   * This is a private constructor since it is singleton

   */

  private DBConnectionPool()  throws SQLException, ClassNotFoundException 

  {

    DBDriver=MetaCatUtil.getOption("dbDriver");

    DBConnectedJDBC=MetaCatUtil.getOption("defaultDB");

    userName=MetaCatUtil.getOption("user");

    passWord=MetaCatUtil.getOption("password");

  }//DBConnection

  /** 

   * Method to establish a JDBC database connection 

   */

  private Connection openConnection()

                  throws SQLException, ClassNotFoundException 

  {

    return openConnection(DBDriver, DBConnectedJDBC, userName, passWord);

  }//openDBConnection

  /** 

   * Method to establish a JDBC database connection 

   *

   * @param dbDriver the string representing the database driver

   * @param connection the string representing the database connectin parameters

   * @param user name of the user to use for database connection

   * @param password password for the user to use for database connection

   */

  private Connection openConnection(String dbDriver, String connection,

                String user, String password)

                throws SQLException, ClassNotFoundException 

 {

     // Load the Oracle JDBC driver

     Class.forName (dbDriver);

     // Connect to the database

     Connection conn = DriverManager.getConnection( connection, user, password);

     return conn;

  }//OpenDBConnection

  /**

   * Method to initial a pool of DBConnection objects 

   */

  public Vector initialDBConnectionPool()

                throws SQLException, ClassNotFoundException 

 {

    Connection conn = null;

    DBConnection dbConn = null;

    for ( int i = 0; i < initialConnectionNumber; i++ ) 

    {

      //open a connection to db

      conn = openConnection();

      //create a new object of DBConnection

      dbConn = new DBConnection();

      //set connetion to DBConnection

      dbConn.setDBConnection(conn);

      //put DBConnection into vetor

      connectionPool.add(dbConn);

    }    

    return connectionPool;

  }

}//DBConnectionPool