connectionpool.java

JAVA平台下优秀的CHART开源代码,可以实现类似EXCEL中的二维或三维的饼图/椎图功能.

/**
 * Copyright (C) 2003  Manfred Andres
 * 
 * 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 freecs.auth.sqlConnectionPool;

import freecs.Server;
import java.sql.*;
import java.util.Properties;
import java.util.Vector;
import java.util.Enumeration;

public class ConnectionPool {
   String url, user, password;
   Properties props;
   PoolElement pool[];
   int p = 0, size =0, idCnt=0, maxStatements;
   long validity;

   public ConnectionPool (int size, String url, String user, String password, int maxStatements, long validity) throws Exception {
      this.url = url;
      this.size = size;
      this.user = user;
      this.password = password;
      this.maxStatements = maxStatements;
      this.validity = validity;
      pool = new PoolElement[size];
   }

	/**
	 * close every connection to the jdbc-source and throw an exception if there was an error
	 * @throws Exception
	 */
   public void shutdown () throws Exception {
      for (int i = 0; i < pool.length; i++) {
         if (pool[i] == null) continue;
         pool[i].cleanup ();
      }
   }

	/**
	 * creates an connectionpool-element
	 * @return the PoolElement connected to the jdbc-datasource
	 * @throws Exception
	 */
   private PoolElement createPoolElement () throws Exception {
      idCnt++;
      if (idCnt == Integer.MAX_VALUE) idCnt = 0;
      Connection con = DriverManager.getConnection (url, user, password);
      return new PoolElement (con, maxStatements, validity, idCnt);
   }

	/**
	 * Gets the next available and valid poolelement or tryes to create a new one
	 * (after connectionpool-size tryes we will throw an exception and login will fail because
	 * of technical error)
	 * @return the valid and available PoolElement
	 * @throws Exception
	 */
	public PoolElement getPoolElement () throws Exception {
		int c = 0, fc = 0;
		if (p >= size) p = 0;
		PoolElement el = null;
		Vector v = new Vector ();
		synchronized (pool) {
			while (el == null) {
				for ( ; c < size; c++, p++) {
					if (p >= size) {
						p = 0;
					}
					el = pool[p];
					if (el == null || !el.isValid ()) try {
						pool[p] = el = createPoolElement ();
					} catch (Exception e) {
						if (!v.contains (e.toString ())) v.addElement (e.toString ());
						continue;
					} else if (el.isActive ()) {
						continue;
					}
					break;
				}
				if (el != null && el.isValid ()) 
					break;
				// if there is an invalid element, we will call cleanup on this poolelement
				// freeing resources and making it possible to reestablis a new PoolElement
				if (el != null) try {
					el.cleanup ();
					el = null;
				} catch (Exception e) {
					Server.debug ("ConnectionPool.getPoolElement: error during cleaning up invalid PoolElement", e, Server.MSG_ERROR, Server.LVL_MAJOR);
					return null;
				}
				fc++;
				if (fc > size) {
					StringBuffer sb = new StringBuffer ("Got no available connection during last ").append (size).append (" runs. The exceptions are as follows:\r\n     ");
					for (Enumeration e = v.elements (); e.hasMoreElements (); ) {
						String ex = (String) e.nextElement ();
						sb.append ("\r\n     ").append (ex);
					}
					throw new Exception (sb.toString ());
				}
			}
			el.setActive ();
			return el;
		}
	}
}