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JDBC connection pooling utility, supporting time-based expiry, statement caching, connection validation, and easy configuration using a pool manager.
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/*
  ---------------------------------------------------------------------------
  DBPool : Java Database Connection Pooling 
  Copyright (c) 2001-2013 Giles Winstanley. All Rights Reserved.

  This is file is part of the DBPool project, which is licensed under
  the BSD-style licence terms shown below.
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  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice,
  this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

  3. The name of the author may not be used to endorse or promote products
  derived from this software without specific prior written permission.

  4. Redistributions of modified versions of the source code, must be
  accompanied by documentation detailing which parts of the code are not part
  of the original software.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER "AS IS" AND ANY EXPRESS OR
  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
  OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
package snaq.db;

import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * {@link ConnectionValidator} implementation that validates database
 * connections by issuing a SQL query, and simply checking if the query
 * succeeded or failed.
 * By default it does not check if any results are returned.
 * This class is provided as a convenience for providing
 * connection validation.
 *
 * @author Giles Winstanley
 */
public class SimpleQueryValidator extends QueryValidator
{
  /** SQL query string to be issued to the database for connection validation. */
  private String query = null;
  /** Flag determining whether to check for returned results. */
  private boolean checkHasResults = false;

  /**
   * Creates a new {@code SimpleQueryValidator} instance using the
   * specified SQL query string. The created instance will not check for
   * existence of returned results, only that the query succeeded.
   * @param query SQL query to issue for validation
   */
  public SimpleQueryValidator(final String query)
  {
    this.query = query;
  }

  /**
   * Creates a new {@code SimpleQueryValidator} instance using the
   * specified SQL query string.
   * @param query SQL query to issue for validation
   * @param checkHasResults whether to check if any results are returned
   */
  public SimpleQueryValidator(String query, boolean checkHasResults)
  {
    this.query = query;
    this.checkHasResults = checkHasResults;
  }

  /**
   * Returns the SQL query string to be issued to the database.
   * @return query string in SQL syntax
   */
  @Override
  public String getQueryString()
  {
    return query;
  }

  /**
   * Checks the results of the SQL query to see if it indicates a valid connection.
   * This implementation simply comprises:
   *    *     return checkHasResults ? results.next() : true;
   * 
   * such that if results-checking was specified when the instance was created
   * then the connection is only validated if some results are returned,
   * otherwise the simply fact of the statement being executed successfully
   * is used for validation.
   * @param results {@code ResultSet} instance produced from SQL query
   * @return boolean indicating whether checked results indicated a valid connection
   * @throws SQLException if checking the results throws such an exception
   */
  @Override
  public boolean checkResults(ResultSet results) throws SQLException
  {
    return checkHasResults ? results.next() : true;
  }
}