dbconnection.java

Town是一个100% 纯Java API

package com.workingdogs.town;

import java.io.*;
import java.sql.*;
import java.util.*;

import com.javaexchange.dbConnectionBroker.*;

/*
Town, a Java JDBC abstraction layer
Copyright (C) 1999  Serge Knystautas, Jon Stevens

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.

This library 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA  02111-1307, USA.
*/

/**
 * This base class handles connection management, creating Connection objects from connection
 * strings (using the connection pooler), and closing connections when complete.  Both the abstract
 * DateSet class extends this, as well as the simple ExecuteStatement class.
 * @author Serge Knystautas <a href="mailto:[e-mail]">[e-mail]</a>
 * @version 1.0
 */
public abstract class DBConnection
{
    /** the Statement for this DBConnection */
    protected Statement stmt = null;
    /** this DBConnection's connection object */
    protected Connection dbconn = null;

    /** flag of whether this DataSet has been closed */
    private boolean closed = false;
    /** this is the connection's driver */
    private String driver = null;
    /** this is the connection's JDBC connection string */
    private String connString = null;
    /** this is the connection's username */
    private String username = null;
    /** this is the connection's password */
    private String password = null;
    /** this is the broker object for this driver, connString, username, and password */
    private DbConnectionBroker broker = null;

    private static Hashtable brokers = new Hashtable ();
    /**
     * DBConnection constructor comment.
     */
    public DBConnection(String driver,
            String connString) throws DataSetException, ConnectionException
    {
        this (driver, connString, null, null);
    }
    /**
      * DBConnection constructor comment.
      */
    public DBConnection(String driver, String connString,
            String username, String password) throws DataSetException,
    ConnectionException
    {
        this.driver = driver;
        this.connString = connString;
        this.username = username;
        this.password = password;

        if (driver == null)
            throw new DataSetException ("You need to specify a valid driver!");

        if (connString == null)
            throw new DataSetException ("You need to specify a valid JDBC connection string!");

        String key = (driver + '\t' + connString).toLowerCase ();

        if (username != null)
            key += '\t' + username.toLowerCase ();
        if (password != null)
            key += '\t' + password.toLowerCase ();

        //	synchronized (brokers)
        //	{
        if (brokers.get (key) != null)
            broker = (DbConnectionBroker) brokers.get (key);
        else
        {
            // The below statement sets up a Broker with a minimun pool size of 2 connections
            // and a maximum of 5.  The log file will be created in
            // D:\JavaWebServer1.1\DCB_Example.log and the pool connections will be
            // restarted once a day.
            try
            {
                broker = new DbConnectionBroker(driver, connString,
                        username, password, 2, 6, "db_pool.log", 1);
            }
            catch (IOException ioe)
            {
                throw new ConnectionException (ioe);
            }
            brokers.put (key, broker);
        }
        //	}

        dbconn = broker.getConnection ();
    }
    /**
       * Releases the records, closes the ResultSet and the Statement and nulls the schema
       *
       * @exception   ConnectionException
       * @exception   DataSetException
       */
    public void close() throws ConnectionException, DataSetException
    {
        try
        {
            this.stmt.close();

        }
        catch (SQLException sqle)
        {
            throw new ConnectionException (sqle);
        }
        catch (NullPointerException npe)
            {}
        finally { broker.freeConnection (dbconn);
            closed = true;
        } }
    /**
       * Gets the current database connection
       *
       * @return     a database connection
       * @exception   ConnectionException
       */
    protected Connection connection() throws ConnectionException
    {
        return dbconn;
    }
    /**
      * This method was created in VisualAge.
      */
    protected void finalize () throws Throwable
    {
        if (!closed)
            close ();
    }
}