dbconnpool.java

1.1 版本的数据库连接池。

package Int.who.database;

/* 
 * The contents of this file are subject to the Mozilla Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/MPL/
 * 
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 * 
 * The Original Code is "The Database Driven Frequently Asked Questions Project of Alex Muc".
 * 
 * The Initial Developer of the Original Code is <a href="mailto:[e-mail]">Alex Muc</a>.
 * Portions created by <a href="mailto:[e-mail]">Alex Muc</a>
 * are Copyright (C) 2000 <a href="mailto:[e-mail]">Alex Muc</a>.
 * All Rights Reserved.
 * 
 * Contributor(s): Alex Muc, Claudia Plesa
 */


import java.sql.*;
import java.util.*;
/**
 * A class which implements a general database connection pool for handling
 * multiple concurrent database connections.  This class is sufficiently general
 * to be able to handle any number of connections to any number of databases.
 * <br><br>
 * Warning:  It is imperative that users of this class call close(ResultSet,
 * ConnectionInfo) when they are done with their RresultSet objects.  This
 * is necessary for cleaning up the database connection.
 * <br><br>
 * This class can handle closing connections to the database to clean
 * itself up.  However, limitations with the FreeTDS (www.freetds.org) driver
 * will mean that it doesn't properly close connections (especially if there has
 * been a network error.  This will confuse things.  The best possible solution
 * is with a single call to DROPALL() which will drop all references to
 * database connections and re-establish all links.
 * <br><br>
 * This class should work quite well, but there is still room for improvement.
 * Particularly in the close connection methods.
 * Creation date: (8/31/2000 1:51:39 PM)
 * @author: Alex Muc [e-mail]
 */
public class DBConnPool {
	public static Vector ResultSets = new Vector();
	public static Vector Connections = new Vector();
	public static Vector Statements = new Vector();
	public static Vector Queries = new Vector();
	public static Vector ConnInfos = new Vector();
	

	/* Stores the number of updates to the database since the last server restart */
	public static int updates;
	/* Stores the number of queries on the database since the last server restart */
	public static int queries;

/**
 * DBConnPool constructor comment.
 */
public DBConnPool() {
	super();
}
/**
 * Close all database connections.
 * This method is not synchronized, so it will kill even active connections.
 * It attempts to play nice and drop it's connection with the database server.
 * These attempts may not work in cases with the FreeTDS driver and network errors.
 * Creation date: (7/18/2000 12:05:54 PM)
 */
public static void close() throws SQLException {
System.out.println("in close");

	
	Iterator conns = Connections.iterator();
	Connection c;
	while (conns.hasNext()) {
		c = (Connection) conns.next();
		c.close();
	}

	conns = Connections.iterator();
	int i = 0;
	Vector indices = new Vector();
	while (conns.hasNext()) {
		c = (Connection) conns.next();
		if (c.isClosed()) {
			indices.addElement(new Integer(i));
		}
		i ++;
	}

	Iterator is = indices.iterator();
	int subtract = 0;
	while (is.hasNext()) {
		i = ((Integer) is.next()).intValue();
		Queries.removeElementAt(i - subtract);
		ResultSets.removeElementAt(i - subtract);
		Statements.removeElementAt(i - subtract);
		Connections.removeElementAt(i - subtract);
		ConnInfos.removeElementAt(i - subtract);
		subtract ++;
	}

}
/**
 * Close all database connections for a give ConnectionInfo object.
 * This method is not synchronized, so it will kill even active connections.
 * Creation date: (7/18/2000 12:05:54 PM)
 */
public static void close(ConnectionInfo ci) throws SQLException {
System.out.println("in close");

	
	Iterator conns = Connections.iterator();
	Iterator cis = ConnInfos.iterator();
	Connection c;
	ConnectionInfo cie;
	while (conns.hasNext()) {
		cie = (ConnectionInfo) cis.next();
		c = (Connection) conns.next();
		if (cie.equals(ci)) {
			c.close();
		}
	}

	conns = Connections.iterator();
	int i = 0;
	Vector indices = new Vector();
	while (conns.hasNext()) {
		c = (Connection) conns.next();
		if (c.isClosed()) {
			indices.addElement(new Integer(i));
		}
		i ++;
	}

	Iterator is = indices.iterator();
	int subtract = 0;
	while (is.hasNext()) {
		i = ((Integer) is.next()).intValue();
		Queries.removeElementAt(i - subtract);
		ResultSets.removeElementAt(i - subtract);
		Statements.removeElementAt(i - subtract);
		Connections.removeElementAt(i - subtract);
		ConnInfos.removeElementAt(i - subtract);
		subtract ++;
	}

}
/**
 * Close a given result set.  This does not close the database connection, but
 * indicates the connection can be re-used.
 * Creation date: (7/18/2000 11:42:29 AM)
 * @param rs java.sql.ResultSet
 */
public synchronized static void close(ResultSet rs, ConnectionInfo ci) throws SQLException {
	
	Iterator rss = ResultSets.iterator();
	Iterator stmts = Statements.iterator();
	java.sql.ResultSet curr;
	int i = 0;
	while (rss.hasNext()) {
		Object o = rss.next();
		if (o instanceof java.sql.ResultSet) {
			curr = (java.sql.ResultSet) o;
			if (curr.equals(rs)) {
				break;
			}
		}
		i ++;
	}

	rs.close();
	ResultSets.setElementAt(null, i);	
	Queries.setElementAt("", i);
}
/**
 * Close a given Statement.  This does not close the database connection, but
 * indicates the connection can be re-used.
 * Creation date: (7/18/2000 11:42:29 AM)
 * @param rs java.sql.ResultSet
 */
private synchronized static void close(java.sql.Statement s) throws SQLException {
	
	Iterator rss = ResultSets.iterator();
	Iterator stmts = Statements.iterator();
	java.sql.Statement curr;
	int i = 0;
	while (stmts.hasNext()) {
		curr = (java.sql.Statement) stmts.next();
		if (curr.equals(s)) {
			break;
		}
		i ++;
	}

//	ResultSet rs = (ResultSet) ResultSets.elementAt(i);
//	rs.close();
	ResultSets.setElementAt(null, i);	
	Queries.setElementAt("", i);
}
/**
 * Drops all references to a given statement.  This is a dirty way to drop
 * a database connection.
 * Creation date: (7/18/2000 11:42:29 AM)
 * @param rs java.sql.ResultSet
 */
private synchronized static void drop(java.sql.Statement s) throws SQLException {
	
	Iterator rss = ResultSets.iterator();
	Iterator stmts = Statements.iterator();
	java.sql.Statement curr;
	int i = 0;
	while (stmts.hasNext()) {
		curr = (java.sql.Statement) stmts.next();
		if (curr.equals(s)) {
			break;
		}
		i ++;
	}

//	ResultSet rs = (ResultSet) ResultSets.elementAt(i);
//	rs.close();
	Connections.removeElementAt(i);
	Statements.removeElementAt(i);
	ResultSets.removeElementAt(i);	
	Queries.removeElementAt(i);
	ConnInfos.removeElementAt(i);
}
/**
 * Completely drops all references to all database connections.  This does not
 * try to clean them up, but only drop all references to them.
 *
 * Note:  For the FreeTDS driver (www.freetds.org) calling this method may still
 * not be enough for re-initializing the database connections due to its poor
 * handling of broken database connections.  In this case a VM restart is the only
 * other option.
 * Creation date: (8/31/2000 5:16:27 PM)
 */
public void DROPALL() {
	
	ResultSets = new Vector();
	Connections = new Vector();
	Statements = new Vector();
	Queries = new Vector();
	ConnInfos = new Vector();
	
}
/**
 * Because the database system treats single-quotes, "'", specially they must be escaped by
 * replacing a single single-quote with two single-quotes (ie. "'" --> "''").  This method
 * handles the escaping of strings.
 * Creation date: (1/26/00 4:35:15 PM)
 * @return java.lang.String The single-quote escaped string.
 * @param query java.lang.String The string to be escaped.
 */
public static String escape(String query) {
	if (query == null)
		return null;
	StringBuffer result = new StringBuffer();
	if (query.indexOf('\'') != -1) {
		for (int i = 0; i < query.length(); i ++){
			if (query.charAt(i) == '\''){
				result.append("''");
			}
			else {
				result.append(query.charAt(i));
			}
		}
		return result.toString();
	}
	return query;
}
/**
 * Centralized method from which all queries to the database are run.  This ensures that the
 * database connection is still active.  It also handles some concurrency issues.  For
 * update queries call executeUpdate(...).
 * Creation date: (1/23/00 5:57:12 PM)
 * @return ResultSet The result of the query from the JDBC call.
 * @param query java.lang.String The query string to execute, can ONLY be query.
 */
public synchronized static ResultSet executeQuery(String query, ConnectionInfo ci) throws SQLException {
	java.sql.Statement s;
	try { 
		s = getStatement(ci);
	} catch (Exception e) {
System.out.println(e);
//		reconnect();
		try {
			s = getStatement(ci);
		} catch (Exception f) {