001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.mapreduce.lib.db;
019    
020    import java.sql.PreparedStatement;
021    import java.sql.ResultSet;
022    import java.sql.SQLException;
023    
024    import org.apache.hadoop.classification.InterfaceAudience;
025    import org.apache.hadoop.classification.InterfaceStability;
026    import org.apache.hadoop.io.Writable;
027    
028    /**
029     * Objects that are read from/written to a database should implement
030     * <code>DBWritable</code>. DBWritable, is similar to {@link Writable} 
031     * except that the {@link #write(PreparedStatement)} method takes a 
032     * {@link PreparedStatement}, and {@link #readFields(ResultSet)} 
033     * takes a {@link ResultSet}. 
034     * <p>
035     * Implementations are responsible for writing the fields of the object 
036     * to PreparedStatement, and reading the fields of the object from the 
037     * ResultSet. 
038     * 
039     * <p>Example:</p>
040     * If we have the following table in the database :
041     * <pre>
042     * CREATE TABLE MyTable (
043     *   counter        INTEGER NOT NULL,
044     *   timestamp      BIGINT  NOT NULL,
045     * );
046     * </pre>
047     * then we can read/write the tuples from/to the table with :
048     * <p><pre>
049     * public class MyWritable implements Writable, DBWritable {
050     *   // Some data     
051     *   private int counter;
052     *   private long timestamp;
053     *       
054     *   //Writable#write() implementation
055     *   public void write(DataOutput out) throws IOException {
056     *     out.writeInt(counter);
057     *     out.writeLong(timestamp);
058     *   }
059     *       
060     *   //Writable#readFields() implementation
061     *   public void readFields(DataInput in) throws IOException {
062     *     counter = in.readInt();
063     *     timestamp = in.readLong();
064     *   }
065     *       
066     *   public void write(PreparedStatement statement) throws SQLException {
067     *     statement.setInt(1, counter);
068     *     statement.setLong(2, timestamp);
069     *   }
070     *       
071     *   public void readFields(ResultSet resultSet) throws SQLException {
072     *     counter = resultSet.getInt(1);
073     *     timestamp = resultSet.getLong(2);
074     *   } 
075     * }
076     * </pre></p>
077     */
078    @InterfaceAudience.Public
079    @InterfaceStability.Stable
080    public interface DBWritable {
081    
082      /**
083       * Sets the fields of the object in the {@link PreparedStatement}.
084       * @param statement the statement that the fields are put into.
085       * @throws SQLException
086       */
087            public void write(PreparedStatement statement) throws SQLException;
088            
089            /**
090             * Reads the fields of the object from the {@link ResultSet}. 
091             * @param resultSet the {@link ResultSet} to get the fields from.
092             * @throws SQLException
093             */
094            public void readFields(ResultSet resultSet) throws SQLException ; 
095    }