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 }