|
What this is
Other links
The source code/* * $Header: /cvsroot/mvnforum/myvietnam/src/net/myvietnam/mvncore/db/DBConnectionManager.java,v 1.13 2005/01/26 04:54:26 minhnn Exp $ * $Author: minhnn $ * $Revision: 1.13 $ * $Date: 2005/01/26 04:54:26 $ * * ==================================================================== * * Copyright (C) 2002-2005 by MyVietnam.net * * 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 any later version. * * All copyright notices regarding MyVietnam and MyVietnam CoreLib * MUST remain intact in the scripts and source code. * * 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. * * Correspondence and Marketing Questions can be sent to: * info@MyVietnam.net * * @author: Minh Nguyen minhnn@MyVietnam.net * @author: Mai Nguyen mai.nh@MyVietnam.net */ package net.myvietnam.mvncore.db; import java.sql.*; import java.util.Enumeration; import java.util.Vector; import net.myvietnam.mvncore.MVNCoreConfig; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * This class is a Singleton that provides access to the * connection pool. A client gets access to the single * instance through the static getInstance() method * and can then check-out and check-in connections from a pool. * When the client shuts down it should call the release() method * to close all opened connections and do other clean up. */ class DBConnectionManager { private static Log log = LogFactory.getLog(DBConnectionManager.class); private static final int TIME_BETWEEN_RETRIES = 500; // O.5 second // static variable static private DBConnectionManager instance = null; // The single instance // instance variable private DBConnectionPool pool = null;// please be careful if u want to make this variable static /** * A private constructor since this is a Singleton * Note: This constructor is lightweight since DBConnectionPool is lightweight, * so no connection is created until the first time getConnection() is called */ private DBConnectionManager(DBOptions option) { try { Class.forName(option.driverClassName).newInstance(); } catch (Exception e) { log.fatal("DBConnectionManager: Unable to load driver = " + option.driverClassName); } //always new the pool because pool is an instance variable pool = new DBConnectionPool(option.databaseURL, option.databaseUser, option.databasePassword, option.maxConnection); } private DBConnectionManager() { String driverClassName = MVNCoreConfig.getDriverClassName(); try { Class.forName(driverClassName).newInstance(); } catch (Exception e) { log.fatal("DBConnectionManager: Unable to load driver = " + driverClassName); } String url = MVNCoreConfig.getDatabaseURL(); String user = MVNCoreConfig.getDatabaseUser(); String password = MVNCoreConfig.getDatabasePassword(); int maxConnection = MVNCoreConfig.getMaxConnection(); //always new the pool because pool is an instance variable pool = new DBConnectionPool(url, user, password, maxConnection); } /** * Returns the single instance, creating one if it's the * first time this method is called. * * @return DBConnectionManager The single instance. */ /* public static synchronized DBConnectionManager getInstance() { if (instance == null) { DBOptions option = new DBOptions(); instance = new DBConnectionManager(option); } return instance; }*/ /** * Returns the single instance, creating one if it's the * first time this method is called. * * @return DBConnectionManager The single instance. */ /* private static synchronized DBConnectionManager getInstance(DBOptions option) { if (instance == null) { if (option == null) { option = new DBOptions(); } instance = new DBConnectionManager(option); } return instance; }*/ public static synchronized DBConnectionManager getInstance(boolean useConfig) { if (instance == null) { instance = new DBConnectionManager(); } return instance; } /** * Returns a connection to the pool. * * @param con The Connection */ void freeConnection(Connection con) { pool.freeConnection(con); } /** * Returns an open connection. If no one is available, and the max * number of connections has not been reached, a new connection is * created. * * @return Connection The connection or null */ Connection getConnection() { return pool.getConnection(); } /** * Returns an open connection. If no one is available, and the max * number of connections has not been reached, a new connection is * created. If the max number has been reached, waits until one * is available or the specified time has elapsed. * * @param time The number of milliseconds to wait * @return Connection The connection or null */ Connection getConnection(long time) { return pool.getConnection(time); } /** * Closes all open connections. * @return true if the pool is empty and balance * false if the pool has returned some connection to outside */ boolean release() { return pool.release(); } /** * This inner class represents a connection pool. It creates new * connections on demand, up to a max number if specified. * It also checks to make sure that the connection is still open * before it is returned to a client. */ class DBConnectionPool { private int checkedOut = 0;//NOTE: this variable should be changed in synchronized method only private Vector freeConnections = new Vector(); private int maxConn = 0; private String password = null; private String URL = null; private String user = null; /** * Creates new connection pool. * NOTE: new an instance of this class is lightweight since it does not create any connections * * @param URL The JDBC URL for the database * @param user The database user, or null * @param password The database user password, or null * @param maxConn The maximal number of connections, or 0 for no limit */ public DBConnectionPool(String URL, String user, String password, int maxConn) { this.URL = URL; this.user = user; this.password = password; this.maxConn = maxConn; } /** * Checks in a connection to the pool. Notify other Threads that * may be waiting for a connection. * * @todo: Maybe we dont need notifyAll(); ??? * * @param con The connection to check in */ synchronized void freeConnection(Connection con) { // Put the connection at the end of the Vector if (con != null) {//make sure that the connection is not null if (checkedOut <= 0) { // this means that connection is open too much // There are 2 cases: // 1. Not get from this connection pool (maybe get directly) // 2. this connection is gotten and then the whole pool is released // In these case, just close the connection try { log.debug("DBConnectionManager: about to close the orphan connection."); con.close(); } catch (SQLException ex) { } } else { // Return this connection to the pool // note that we dont have to check if the connection is not connected // this will be check in the getConnection method freeConnections.addElement(con); // FIXME: posible negative value // NOTE: checkOut should never be negative here checkedOut--; // NOTE: this number can be negative (in case connection does not come from the pool) notifyAll(); // can I remove it ??? } } } /** * Checks out a connection from the pool. If no free connection * is available, a new connection is created unless the max * number of connections has been reached. If a free connection * has been closed by the database, it's removed from the pool * and this method is called again recursively. */ synchronized Connection getConnection() { Connection con = null; while ( (freeConnections.size() > 0) && (con == null) ) { // Pick the first Connection in the Vector // to get round-robin usage con = (Connection) freeConnections.firstElement(); freeConnections.removeElementAt(0); try { if (con.isClosed()) { log.info("Removed bad connection in DBConnectionPool."); con = null; // to make the while loop to continue } } catch (SQLException e) { con = null; // to make the while loop to continue } } // while if (con == null) {// cannot get any connection from the pool if (maxConn == 0 || checkedOut < maxConn) {// maxConn = 0 means unlimited connections con = newConnection(); } } if (con != null) { checkedOut++; } return con; } /** * Checks out a connection from the pool. If no free connection * is available, a new connection is created unless the max * number of connections has been reached. If a free connection * has been closed by the database, it's removed from the pool * and this method is called again recursively. * <P> * If no connection is available and the max number has been * reached, this method waits the specified time for one to be * checked in. * * @param timeout The timeout value in milliseconds */ /** * Note that this method is not synchronized since it relies on the getConnection(void) method * I also believe that this method SHOULD NOT synchronized because I use #sleep() method * @todo: check if we should synchronize this method and use wait instead of sleep ??? */ Connection getConnection(long timeout) { long startTime = System.currentTimeMillis(); Connection con; while ((con = getConnection()) == null) { long elapsedTime = System.currentTimeMillis() - startTime; if (elapsedTime >= timeout) { // Timeout has expired return null; } long timeToWait = timeout - elapsedTime; if (timeToWait > TIME_BETWEEN_RETRIES) timeToWait = TIME_BETWEEN_RETRIES;// we dont want to wait for more than TIME_BETWEEN_RETRIES second each time try { Thread.sleep(timeToWait); } catch (InterruptedException e) {} } return con; } /** * Closes all available connections. * @return true if the pool is empty and balance * false if the pool has returned some connection to outside */ synchronized boolean release() { boolean retValue = true; Enumeration allConnections = freeConnections.elements(); while (allConnections.hasMoreElements()) { Connection con = (Connection) allConnections.nextElement(); try { con.close(); } catch (SQLException e) { log.error("Cannot close connection in DBConnectionPool."); } } freeConnections.removeAllElements(); if (checkedOut != 0) { retValue = false; log.warn("DBConnectionManager: the built-in connection pool is not balanced."); } checkedOut = 0; return retValue; } /** * Creates a new connection, using a userid and password * if specified. * @todo: check if this method need synchronized */ private Connection newConnection() { Connection con = null; try { if (user == null) { con = DriverManager.getConnection(URL); } else { con = DriverManager.getConnection(URL, user, password); } con.setAutoCommit(true);//thread 804 by trulore } catch (SQLException e) { log.error("Cannot create a new connection in DBConnectionPool. URL = " + URL, e); return null; } return con; } } } |
... this post is sponsored by my books ... | |
#1 New Release! |
FP Best Seller |
Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.
A percentage of advertising revenue from
pages under the /java/jwarehouse
URI on this website is
paid back to open source projects.