public   class  DBConnectionPool  implements  ConnectionPool {
	
	 private  String url;
	 private  String user;
	 private  String pass;
	 private   static  DBConnectionPool instance =  null ;
	 private  ArrayList freeConnections =  null ;


	 private  DBConnectionPool(String url, String user, String pass,  int  conNumber) {
		 this .url = url;
		 this .user = user;
		 this .pass = pass;
		loadDriver();
		freeConnections =  new  ArrayList(conNumber);
		 for  ( int  i= 0 ; i<conNumber; i++) {
			Connection conn =  null ;
			 try  {
				conn = newConnection();
				conn.setAutoCommit(false);
			}  catch  (Exception e) {
				e.printStackTrace();
			} //try
			freeConnections.add(conn);
		} //for
	}


	 private   void  loadDriver() {
		 try  {
			Driver driver = (Driver) Class .forName("oracle.jdbc.driver.OracleDriver").newInstance();
			DriverManager.registerDriver(driver);
		}  catch  (Exception e) {
			e.printStackTrace();
		} //try
	}


	 public   static   synchronized  DBConnectionPool getInstance(String url, String user, String pass,  int  conNumber) {
		 if  (instance ==  null ) {
			instance =  new  DBConnectionPool(url, user, pass, conNumber);
		}
		 return  instance;
	};


	 public   synchronized  Connection getConnection() {
		Connection conn =  null ;
		 if  (!freeConnections.isEmpty()) {
			conn = (Connection)freeConnections.get(freeConnections.size() -  1 );			
			freeConnections.remove(conn);
			 try  {
				 if  (conn.isClosed()) {
					conn = getConnection();
				}
			}  catch  (Exception e) {
				conn = getConnection();
			} //try
		}  else  {
			conn = newConnection();
		}
		 return  conn;
	}


	 private  Connection newConnection() {
		Connection conn =  null ;
		 try  {
			conn = DriverManager.getConnection(url, user, pass);
		}  catch  (Exception e) {
			e.printStackTrace();
			 return   null ;
		} //try
		 return  conn;
	}


	 public   synchronized   void  freeConnection(Connection conn) {
		 if  (conn !=  null ) {
			 try  {
				conn.commit();
			}  catch  (Exception e) {
			} //try
			freeConnections.add(conn);
		}
	}


	 public   synchronized   void  release() {
		Iterator i = freeConnections.iterator();
		 while  (i.hasNext()) {
			Connection conn = (Connection)i.next();
			 try  {
				conn.close(); conn =  null ;
			}  catch  (Exception e) {
				e.printStackTrace();
			} //try
		} // while
		freeConnections.clear();
	}
};