ResultHandler.java

/*
 * Copyright (c) 2004, PostgreSQL Global Development Group
 * See the LICENSE file in the project root for more information.
 */
// Copyright (c) 2004, Open Cloud Limited.

package org.postgresql.core;

import java.sql.SQLException;
import java.sql.SQLWarning;
import java.util.List;

/**
 * Callback interface for passing query results from the protocol-specific layer to the
 * protocol-independent JDBC implementation code.
 * <p>
 * In general, a single query execution will consist of a number of calls to handleResultRows,
 * handleCommandStatus, handleWarning, and handleError, followed by a single call to
 * handleCompletion when query execution is complete. If the caller wants to throw SQLException,
 * this can be done in handleCompletion.
 * <p>
 * Each executed query ends with a call to handleResultRows, handleCommandStatus, or handleError. If
 * an error occurs, subsequent queries won't generate callbacks.
 *
 * @author Oliver Jowett (oliver@opencloud.com)
 */
public interface ResultHandler {
  /**
   * Called when result rows are received from a query.
   *
   * @param fromQuery the underlying query that generated these results; this may not be very
   *        specific (e.g. it may be a query that includes multiple statements).
   * @param fields column metadata for the resultset; might be <code>null</code> if
   *        Query.QUERY_NO_METADATA was specified.
   * @param tuples the actual data
   * @param cursor a cursor to use to fetch additional data; <code>null</code> if no further results
   *        are present.
   */
  void handleResultRows(Query fromQuery, Field[] fields, List<byte[][]> tuples,
      ResultCursor cursor);

  /**
   * Called when a query that did not return a resultset completes.
   *
   * @param status the command status string (e.g. "SELECT") returned by the backend
   * @param updateCount the number of rows affected by an INSERT, UPDATE, DELETE, FETCH, or MOVE
   *        command; -1 if not available.
   * @param insertOID for a single-row INSERT query, the OID of the newly inserted row; 0 if not
   *        available.
   */
  void handleCommandStatus(String status, int updateCount, long insertOID);

  /**
   * Called when a warning is emitted.
   *
   * @param warning the warning that occurred.
   */
  void handleWarning(SQLWarning warning);

  /**
   * Called when an error occurs. Subsequent queries are abandoned; in general the only calls
   * between a handleError call and a subsequent handleCompletion call are handleError or
   * handleWarning.
   *
   * @param error the error that occurred
   */
  void handleError(SQLException error);

  /**
   * Called before a QueryExecutor method returns. This method may throw a SQLException if desired;
   * if it does, the QueryExecutor method will propagate that exception to the original caller.
   *
   * @throws SQLException if the handler wishes the original method to throw an exception.
   */
  void handleCompletion() throws SQLException;

  /**
   * Callback for batch statements. In case batch statement is executed in autocommit==true mode,
   * the executor might commit "as it this it is best", so the result handler should track which
   * statements are executed successfully and which are not.
   */
  void secureProgress();

  /**
   * Returns the first encountered exception. The rest are chained via {@link SQLException#setNextException(SQLException)}
   * @return the first encountered exception
   */
  SQLException getException();

  /**
   * Returns the first encountered warning. The rest are chained via {@link SQLException#setNextException(SQLException)}
   * @return the first encountered warning
   */
  SQLWarning getWarning();
}