Java tutorial
package com.abel.hwfs.custom.output; /** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import java.io.IOException; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.SQLException; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.JobContext; import org.apache.hadoop.mapreduce.OutputCommitter; import org.apache.hadoop.mapreduce.OutputFormat; import org.apache.hadoop.mapreduce.RecordWriter; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.mapreduce.lib.db.DBWritable; import org.apache.hadoop.mapreduce.lib.output.FileOutputCommitter; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.util.StringUtils; /** * A OutputFormat that sends the reduce output to a SQL table. * <p> * {@link MyDBOutputFormat} accepts <key,value> pairs, where * key has a type extending DBWritable. Returned {@link RecordWriter} * writes <b>only the key</b> to the database with a batch SQL query. * */ @InterfaceAudience.Public @InterfaceStability.Stable public class SetSizeDBOutputFormat<K extends DBWritable, V> extends OutputFormat<K, V> { private static final Log LOG = LogFactory.getLog(SetSizeDBOutputFormat.class); @Override public void checkOutputSpecs(JobContext context) throws IOException, InterruptedException { } @Override public OutputCommitter getOutputCommitter(TaskAttemptContext context) throws IOException, InterruptedException { return new FileOutputCommitter(FileOutputFormat.getOutputPath(context), context); } /** * A RecordWriter that writes the reduce output to a SQL table */ @InterfaceStability.Evolving public class DBRecordWriter extends RecordWriter<K, V> { private Connection connection; private PreparedStatement statement; /** * By default, buffer spills are disabled; everything is spilled * only in close(). */ static final int DEFAULT_MAX_BUFFER_SIZE = 1024; /** Number of statements in the current execution batch. */ private int numBufferedStatements; /** * Number of statements after which a db spill will be triggered. * Set to zero to disable intermediate spills. */ private int maxBufferedStatements; public DBRecordWriter() throws SQLException { this(null, null); } public DBRecordWriter(Connection connection, PreparedStatement statement) throws SQLException { this(connection, statement, DEFAULT_MAX_BUFFER_SIZE); } public DBRecordWriter(Connection connection, PreparedStatement statement, int maxBuffer) throws SQLException { this.connection = connection; this.statement = statement; if (null != this.connection) { this.connection.setAutoCommit(false); } this.numBufferedStatements = 0; if (maxBuffer < 0) { this.maxBufferedStatements = DEFAULT_MAX_BUFFER_SIZE; LOG.warn("Max buffer size of " + maxBuffer + " is invalid; setting to " + DEFAULT_MAX_BUFFER_SIZE); } else { this.maxBufferedStatements = maxBuffer; } } public Connection getConnection() { return connection; } public PreparedStatement getStatement() { return statement; } /** * Cause the current buffer of prepared statements to be sent * to the database. */ protected void spill() throws IOException { LOG.debug("Spilling " + this.numBufferedStatements + " records to database."); try { statement.executeBatch(); connection.commit(); statement.clearBatch(); numBufferedStatements = 0; } catch (SQLException e) { try { connection.rollback(); } catch (SQLException ex) { LOG.warn(StringUtils.stringifyException(ex)); } throw new IOException(e.getMessage()); } LOG.debug("Spill complete."); } /** Trigger a spill if our buffer is oversize. */ protected void maybeSpill() throws IOException { if (maxBufferedStatements != 0 && numBufferedStatements > maxBufferedStatements) { spill(); } } /** {@inheritDoc} */ @Override public void close(TaskAttemptContext context) throws IOException { try { spill(); } finally { try { statement.close(); connection.close(); } catch (SQLException ex) { throw new IOException(ex.getMessage()); } } } /** {@inheritDoc} */ @Override public void write(K key, V value) throws IOException { try { key.write(statement); statement.addBatch(); numBufferedStatements++; maybeSpill(); } catch (SQLException e) { e.printStackTrace(); } } } /** * Constructs the query used as the prepared statement to insert data. * * @param table * the table to insert into * @param fieldNames * the fields to insert into. If field names are unknown, supply an * array of nulls. */ public String constructQuery(String table, String[] fieldNames) { if (fieldNames == null) { throw new IllegalArgumentException("Field names may not be null"); } StringBuilder query = new StringBuilder(); query.append("INSERT INTO ").append(table); if (fieldNames.length > 0 && fieldNames[0] != null) { query.append(" ("); for (int i = 0; i < fieldNames.length; i++) { query.append(fieldNames[i]); if (i != fieldNames.length - 1) { query.append(","); } } query.append(")"); } query.append(" VALUES ("); for (int i = 0; i < fieldNames.length; i++) { query.append("?"); if (i != fieldNames.length - 1) { query.append(","); } } query.append(");"); return query.toString(); } /** {@inheritDoc} */ @Override public RecordWriter<K, V> getRecordWriter(TaskAttemptContext context) throws IOException { MyDBConfiguration dbConf = new MyDBConfiguration(context.getConfiguration()); String tableName = dbConf.getOutputTableName(); String[] fieldNames = dbConf.getOutputFieldNames(); int maxBufferSize = dbConf.getOutputBufferLimit(); if (fieldNames == null) { fieldNames = new String[dbConf.getOutputFieldCount()]; } try { Connection connection = dbConf.getConnection(); PreparedStatement statement = null; statement = connection.prepareStatement(constructQuery(tableName, fieldNames)); return new DBRecordWriter(connection, statement, maxBufferSize); } catch (Exception ex) { throw new IOException(ex.getMessage()); } } /** * Initializes the reduce-part of the job with * the appropriate output settings * * @param job The job * @param tableName The table to insert data into * @param fieldNames The field names in the table. */ public static void setOutput(Job job, String tableName, String... fieldNames) throws IOException { if (fieldNames.length > 0 && fieldNames[0] != null) { MyDBConfiguration dbConf = setOutput(job, tableName); dbConf.setOutputFieldNames(fieldNames); } else { if (fieldNames.length > 0) { setOutput(job, tableName, fieldNames.length); } else { throw new IllegalArgumentException("Field names must be greater than 0"); } } } /** * Initializes the reduce-part of the job * with the appropriate output settings * * @param job The job * @param tableName The table to insert data into * @param fieldCount the number of fields in the table. */ public static void setOutput(Job job, String tableName, int fieldCount) throws IOException { MyDBConfiguration dbConf = setOutput(job, tableName); dbConf.setOutputFieldCount(fieldCount); } private static MyDBConfiguration setOutput(Job job, String tableName) throws IOException { job.setOutputFormatClass(SetSizeDBOutputFormat.class); job.setReduceSpeculativeExecution(false); MyDBConfiguration dbConf = new MyDBConfiguration(job.getConfiguration()); dbConf.setOutputTableName(tableName); return dbConf; } }