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Demo

DB.java

package edu.virtualschool.jwaa.dbms;

import java.io.File;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;

import org.apache.log4j.Logger;

import edu.virtualschool.jwaa.Config;

public  final class DB 
{
  private final DBPool pool;
  public Connection connection;
  
  final Logger logger = Logger.getLogger(DB.class.getName());
  
  public DB(File file) throws Config.Fault, DBPool.Fault, DB.Fault
  {
    this(new Config(file));
  }
  public DB(String path) throws Config.Fault, DBPool.Fault, DB.Fault
  {
    this(new Config(path));
  }
  public DB(Config config) throws Config.Fault, DBPool.Fault, DB.Fault
  {
    this(new DBPool(config));
  }
  public DB(DBPool pool)  throws DBPool.Fault, DB.Fault
  {
    this.pool = pool;
    try
    {
      this.connection = pool.checkout();
    }
    catch (DBPool.Fault e)
    {
      logger.error("new DB(pool) failed, retrying...", e);
      try
      {
        this.connection = pool.checkout();
      }
      catch (DBPool.Fault e1)
      {
        logger.error("new DB(pool) retry failed, giving up", e1);
        throw e;
      }
    }
  }
  public  final void commit() throws DB.Fault
  {
    if (connection == null)
      throw new DB.Fault("commit to a null connection");
    try
    {
      connection.commit();
    }
    catch (SQLException e)
    {
      throw new Fault(e, e);
    }
  }
  public  final void rollback() throws DB.Fault
  {
    if (connection == null)
      throw new DB.Fault("rollback to a null connection");
    try
    {
      connection.rollback();
    }
    catch (SQLException e)
    {
      throw new DB.Fault("rollback failed", e);
    }
  }
  public  final void close() throws DB.Fault
  {
    if (connection != null)
    {
      pool.checkin(connection);
      connection = null;
    }
  }
  public final void finalize()
  {
    try
    {
      close();
    }
    catch (Throwable e)
    {
      logger.error(e, e);
    }
  }
  public  final DBQuery query(String sql)
    throws DB.Fault
  {
    return new DBQuery(this, sql);
  }
  public  final DBUpdate update(String sql)
    throws DB.Fault
  {
    return new DBUpdate(this, sql);
  }
  
  public  final void execute(String sql)
    throws DB.Fault
  {
    try
    {
      Statement stmt = connection.createStatement();
      stmt.execute(sql);
      stmt.close();
    }
    catch (SQLException e)
    {
      throw new Fault(sql, e);
    }
  }
  public final void lock(Object[] tables) throws Fault
  {
    final StringBuffer sql = new StringBuffer("lock tables ");
    for (int i = 0; i < tables.length; i++)
      sql.append(tables[i] + " write" + (i < tables.length - 1 ? ", " : ""));
    execute(sql.toString());
  }
  public final void unlock() throws Fault
  {
    execute("unlock tables");
  }
  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); }
  }
}