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DBPool.java

package edu.virtualschool.jwaa.dbms;

import java.io.File;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.Vector;

import edu.virtualschool.jwaa.Config;

public class DBPool
{
  boolean isInitialized = false;
  final String url;
  final String password;
  final String user;
  final int maxConnections;
  final String[] driverList;
  final Vector pooledConnections = new Vector();
  public int numberBusyConnections;
  
  public DBPool(String path) throws Config.Fault, Fault
  {
    this(Config.loadFile(path));
  }
  public DBPool(File path) throws  Config.Fault, Fault
  {
    this(Config.loadFile(path));
  }
  public DBPool(Config config) throws  Config.Fault, Fault
  {
    this(
      config.get("url"),
      config.get("user"),
      config.get("pass"),
      config.get("connections"),
      new String[] { config.get("driver") }
    );
  }
  public DBPool(
    String url,
    String user,
    String password,
    String maxConnections,
    String[] driverList
  ) throws Fault
  {
    this.driverList = driverList;
    if (driverList == null)
      throw new Fault("driverList may not be null");
    if (driverList.length <= 0)
      throw new Fault("driverList length may not be zero");

    this.url = url;
    if ( url == null)
      throw new Fault("url may not be null");

    this.user = user;
    if (user == null)
      throw new Fault("user may not be null");

    this.password = password;
    if (password == null)
      throw new Fault("password may not be null");

    this.numberBusyConnections = 0;
    this.isInitialized = false;

    if (maxConnections == null)
      throw new Fault("maxConnections may not be null");
    try
    {
      this.maxConnections = Integer.parseInt(maxConnections);
    }
    catch (NumberFormatException e1)
    {
      throw new Fault(maxConnections+" is not an integer");
    }
  }
  public Connection checkout() throws Fault { return checkout(10*1000); }
  public synchronized Connection checkout(long timeout) throws Fault
  {
    long startTime = System.currentTimeMillis();
    Connection connection = null;
    while((connection = getConnection()) == null)
    {
      try 
      {
        super.wait(timeout); 
      }
      catch (InterruptedException e)
      {
        e.printStackTrace(); 
      }
      if ((System.currentTimeMillis() - startTime) >= timeout)
        throw new Fault("Connection pool timeout: " + timeout, null);
    }
    numberBusyConnections++;
    try
    {
      connection.setAutoCommit(false);
      connection.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);
    }
    catch (SQLException e)
    {
      throw new DBPool.Fault
        ("Fault setting up connection #"+numberBusyConnections, e);
    }
    return connection;
  }
  public synchronized void checkin(Connection connection)
  {
    if (connection != null) // paranoia
    {
      pooledConnections.add(connection);
      numberBusyConnections--;
      super.notifyAll();
    }
  }
  public final String toString() { return url; }
  public final int getMaxConnections() { return maxConnections; }
  public final int getNumberBusyConnections() { return numberBusyConnections; }
  public final int getNumberPooledConnections() { return pooledConnections.size(); }

  private Connection getConnection() throws Fault
  {
    Connection connection = null;
    while (pooledConnections.size() > 0 && connection == null)
    {
      connection = (Connection) pooledConnections.firstElement();
      pooledConnections.removeElementAt(0);
      try 
      { 
        if (connection.isClosed()) 
          connection = null; 
      }
      catch (SQLException e)
      { 
        throw new Fault(e, e);
      }
    }
    if (connection == null)
    {
      if (maxConnections == 0 || numberBusyConnections < maxConnections)
        connection = addConnection();
    }
    return connection;
  }
  private Connection addConnection() throws Fault
  {
    if (!isInitialized) 
      initialize();
    Connection connection = null;
    try
    {
      if (user == null || password == null) 
        connection =DriverManager.getConnection(url);
      else 
        connection = DriverManager.getConnection(url, user, password);

      if (connection == null)
        throw new Fault("DriverManager.getConnection("+url+") fault");

      return connection;
    }
    catch (SQLException e)
    { throw new Fault(e, e); }
  }
  private final void initialize() throws Fault
  {
    for (int i = 0; i < driverList.length; i++)
    {
      String driverClassName = driverList[i];
      try
      {
        Driver driver = (Driver)Class.forName(driverClassName).newInstance();
        DriverManager.registerDriver(driver);
      }
      catch (Exception e)
      { throw new Fault("Couldn't register: " + driverClassName, e); }
    }
    isInitialized = true;
  }
  public synchronized void releaseAllConnections() throws Fault
  {
    for (Enumeration e = pooledConnections.elements(); e.hasMoreElements(); )
    {
      Connection c = (Connection) e.nextElement();
      try { c.close(); }
      catch (SQLException ex)
      { throw new Fault(ex, ex); }
    }
    pooledConnections.removeAllElements();
  }
  public final static class Fault extends edu.virtualschool.jwaa.Fault
  {
    public Fault(Object m, Throwable e) { super(m, e); }
    public Fault(Object m) { super(m, null); }
    public Fault(Throwable e) { super(e, e); }
  }
}