pooledconnection.java

一个论坛程序的简单实现

/*
 * Copyright (c) 2003, Rafael Steil
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, 
 * with or without modification, are permitted provided 
 * that the following conditions are met:
 * 
 * 1) Redistributions of source code must retain the above 
 * copyright notice, this list of conditions and the 
 * following  disclaimer.
 * 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) Neither the name of "Rafael Steil" nor 
 * the names of its contributors may be used to endorse 
 * or promote products derived from this software without 
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT 
 * HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, 
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 
 * THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, 
 * OR PROFITS; OR BUSINESS INTERRUPTION) 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
 * 
 * This file creation date: Mar 3, 2003 / 14:43:35 AM
 * The JForum Project
 * http://www.jforum.net
 */

package net.jforum;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Date;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Timer;
import java.util.TimerTask;

import net.jforum.util.preferences.ConfigKeys;
import net.jforum.util.preferences.SystemGlobals;

import org.apache.log4j.Logger;

/** 
 * Every query and connection come from here.
 * Before you can get some connection from the pool, you must
 * call init() to initialize the connections. After that, 
 * to get a conneciton, simple use
 *
 * <blockquote><pre>
 * 		Connection con = PooledConnection.getConnection();
 * </pre></blockquote>
 *
 * The name of the query is associated with a Prepared Statement string, which is inside 
 * of a properties file, called [dbtype].sql, where the type is specified inside of 
 * database.properties.<br>
 * <br>
 * Also manages the connection to the database. The configuration is a config file which
 * is read at the first <code>init()</code> call. You must init it before using the pool.<p>
 *
 * <code>PooledConnection</code> is for now a singleton.
 *
 * @author Paulo Silveira
 * @author Rafael Steil
 * @version $Id: PooledConnection.java,v 1.10 2004/09/22 23:18:23 rafaelsteil Exp $
 * */

public class PooledConnection extends DBConnection
{
	private static PooledConnection pool;
	
	private int minConnections, maxConnections, timeout;
	private String connectionString;
	
	private static final Logger logger = Logger.getLogger(PooledConnection.class);

	/**
	* It is the connection pool
	*/
	private static LinkedList connections = new LinkedList();
    
	/**
	 * It has all the connections, even the ones in use.
	 * This way, the garbage collector does not get them.
	 */
	private static LinkedList allConnections = new LinkedList();

	// for sinalizing a release
	private Object releaseSignal = new Object();
	
	private static final boolean debug = false;
	
	/**
	 * Private constructor that loads the driver and set the configuration from
	 * the properties file. It will also initialize the Database driver.
	 * 
	 * @param dbConfigFile The full path plus the filename to the file which contains database specifc parameters
	 * @throws IOException
	 * @throws Exception
	*/
	public PooledConnection() {}

    /**
     * Inits ConnectionPool. 
     * If the pool was already initialized, this action will take no effect.
	 *
	 * @throws Exception
     */
    public void init() throws Exception
    {
		String driver = SystemGlobals.getValue(ConfigKeys.DATABASE_CONNECTION_DRIVER);
		
		try {
			Class.forName(driver);
			
			this.minConnections = SystemGlobals.getIntValue("database.connection.pool.min");
			this.maxConnections = SystemGlobals.getIntValue("database.connection.pool.max");
			this.timeout = SystemGlobals.getIntValue("database.connection.pool.timeout");

			this.connectionString = SystemGlobals.getValue(ConfigKeys.DATABASE_CONNECTION_STRING);
			
			if (debug) {
				logger.info("*********************************************");
				logger.info("******** STARTING CONNECTION POOL ***********");
				logger.info("*********************************************");
				logger.info("database.connection.driver = "+ driver);
				logger.info("minConnections = "+ this.minConnections);
				logger.info("maxConnections = "+ this.maxConnections);
				logger.info("timeout = "+ this.timeout);
				logger.info("*********************************************");
			}

			for (int i = 0; i < this.minConnections; i++) {
				Connection conn = DriverManager.getConnection(this.connectionString);
				connections.addLast(conn);
				allConnections.add(conn);
				
				if (debug) {
					Date now = new Date();
					logger.info(now.toString() + " opening connection "+ (i + 1));
				}
			}
			
			this.isDatabaseUp = true;
		}
		catch (ClassNotFoundException e) {
			this.isDatabaseUp = false;
			
			logger.error("Ouch... Cannot find database driver: "+ driver);
			throw new IOException("Ouch... Cannot find database driver: "+ driver);
		}
		
		this.enableConnectionPinging();
    }

	/**
	 * Gets a connection to the database.<p> 
	 * 
	 * So you need to release it, after use. It will not be a huge problem if you do not
	 * release it, but this way you will get a better performance.<p>
	 * Thread safe.
	 *
	 * @return <code>Connection</code> object
	 * @throws java.sql.SQLException	 
	 */
	public synchronized Connection getConnection() throws SQLException 
	{
		Connection conn = null;

		// if there is enought Connections
		if (connections.size() != 0) {
			synchronized (connections) {
				conn = (Connection) connections.removeFirst();
			}

			// take a look if the connection has died!
			try {
				if (conn.isClosed()) {
					synchronized (allConnections) {
						allConnections.remove(conn);
						conn = DriverManager.getConnection(this.connectionString);
						allConnections.add(conn);
					}
				}
			}
			catch (SQLException e) {
				if (debug) {
					logger.warn("Cannot reconnect a closed connection:" + this.connectionString + e);
				}
				
				throw e;
			}

			return conn;
		}
        // Otherwise, create a new one if the Pool is now full
		else {
			if (allConnections.size() < this.maxConnections) {
				try {
					conn = DriverManager.getConnection(this.connectionString);
				}
				catch (SQLException e) {
					if (debug) {
						logger.warn("Cannot stabilish a NEW connection to the database:" + this.connectionString + e);
					}
					
                    throw e;
				}
				
				// registering the new connection
				synchronized (allConnections) {
					allConnections.add(conn);
				}
				
				return conn;
			}
		}

        /*
         * Trying to get some Connections stuck inside some Queries.
         * The Query.finalize method will release them.
         * We need to wait sometime, so the GC will get the Connections for us
         */
		System.gc();

		synchronized (this.releaseSignal) {
			/*
			 * Not inside a while, since we are giving it a maximum timeout, 
			 * and this method is already SYNC, there is no way that we will loose
			 * the state if we receive a signal
			 */
			if (connections.size() == 0) {
				try {
					this.releaseSignal.wait(this.timeout);
				}
				catch (InterruptedException e) {
					if (debug)
						logger.warn("Problems while waiting for connection. "+ e);
				}
			}

			if (connections.size() == 0) {
				// TIMED OUT!!!!
				if (debug) {
					logger.warn( "Pool is empty, and th waiting for one timed out!"
						+ "If this is happening too much, your code is probably not releasing the Connections."
						+ "If you cant solve this, set your 'database.connection.pool.timeout' to a bigger number.");
				}
			}
			else {
				synchronized (connections) {
					conn = (Connection) connections.removeFirst();
				}
				
				return conn;
			}
		}
		
		return conn;
	}
	
	private void pingConnections() {
		try {
			this.realReleaseAllConnections();
		} catch (Exception e) { e.printStackTrace(); }
		
		try {
			this.init();
		}
		catch (Exception e) { e.printStackTrace(); }
	} 
	
	public void enableConnectionPinging() {
		new Timer(true).schedule(new TimerTask() {
			public void run() {
				pingConnections();
			}
		}, Long.parseLong(SystemGlobals.getValue(ConfigKeys.DATABASE_PING_DELAY)));
	} 
	
	/** 
	 * @see net.jforum.DBConnection#realReleaseAllConnections()
	 */
	public void realReleaseAllConnections() throws Exception 
	{
		if (allConnections == null || allConnections.size() == 0) {
			return;	
		}

		synchronized (allConnections) {
			for (Iterator iter = allConnections.iterator(); iter.hasNext();) {
				try {
					Connection conn = (Connection)iter.next();
					connections.remove(conn);
					conn.close();
					iter.remove();
					
					logger.info("Real closing connection...");
				}
				catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
		
		allConnections = new LinkedList();
		connections = new LinkedList();
	}

	/**
	 * Releases a connection, making it available to the pool once more.
	 *
	 * @param conn <code>Connection</code> object to release
	 * @throws java.sql.SQLException
	 */
	public void releaseConnection(Connection conn) throws SQLException 
	{
		if (conn == null) {
			if (debug) {
				logger.warn("Cannot release a NULL connection!");
			}
				
			return;
		}

		// Sync because collection.contains() uses the fail fast iterator!
		synchronized (allConnections) {
			if (!allConnections.contains(conn) && debug) {
				logger.warn("Cannot release a connection that is not from this pool!");
				
				return;
			}
			
			try {
				if (conn.isClosed()) {
					allConnections.remove(conn);
					
					return;
				}
			}
			catch (SQLException e) {
				if (debug) {
					logger.warn("Cannot get info about the conn: "+ e);
				}
			}
		}
		
		synchronized (this.releaseSignal) {
			synchronized (connections) {
				connections.addLast(conn);
			}
			
			this.releaseSignal.notify();
		}
	}

	/**
	 * Returns the status
	 * 
	 * @return The status
	 */
	public synchronized String getStatus() 
	{
		StringBuffer status = new StringBuffer();
		int i = 0;

		Iterator it = allConnections.iterator();
		while (it.hasNext()) {
			i++;
			status.append("Connection " + i + ": ");

			Connection c = (Connection) it.next();
			if (c != null) {
				try {
                    status.append(c + " closed: " + c.isClosed());
				}
				catch (SQLException e) {
                    status.append(e);
				}
			}
			else {
				status.append("NULL!!!");
			}

			status.append("\n");
		}

		status.append("\nPOOL:\n\n");
		i = 0;

		it = connections.iterator();
		while (it.hasNext()) {
			i++;
			status.append("Connection " + i + ": ");

			Connection c = (Connection) it.next();
			if (c != null) {
				try {
					status.append(c + " closed: " + c.isClosed());
				}
				catch (SQLException e) {
					status.append(e);
				}
			}
			else
				status.append("NULL!!!");

			status.append("\n");
		}
        
		return status.toString();
	}
}