Java tutorial
/** * 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. */ package org.apache.avro.mapred; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.util.Map; import java.net.URLDecoder; import org.apache.hadoop.io.NullWritable; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.mapred.JobConf; import org.apache.hadoop.mapred.Reporter; import org.apache.hadoop.mapred.FileOutputFormat; import org.apache.hadoop.mapred.RecordWriter; import org.apache.hadoop.util.Progressable; import org.apache.avro.Schema; import org.apache.avro.file.DataFileWriter; import org.apache.avro.file.CodecFactory; import org.apache.avro.generic.GenericData; import org.apache.avro.hadoop.file.HadoopCodecFactory; import static org.apache.avro.file.DataFileConstants.DEFAULT_SYNC_INTERVAL; import static org.apache.avro.file.DataFileConstants.DEFLATE_CODEC; /** * An {@link org.apache.hadoop.mapred.OutputFormat} for Avro data files. * <p/> * You can specify various options using Job Configuration properties. * Look at the fields in {@link AvroJob} as well as this class to get * an overview of the supported options. */ public class AvroOutputFormat<T> extends FileOutputFormat<AvroWrapper<T>, NullWritable> { /** The file name extension for avro data files. */ public final static String EXT = ".avro"; /** The configuration key for Avro deflate level. */ public static final String DEFLATE_LEVEL_KEY = "avro.mapred.deflate.level"; /** The configuration key for Avro sync interval. */ public static final String SYNC_INTERVAL_KEY = "avro.mapred.sync.interval"; /** The default deflate level. */ public static final int DEFAULT_DEFLATE_LEVEL = 1; /** Enable output compression using the deflate codec and specify its level.*/ public static void setDeflateLevel(JobConf job, int level) { FileOutputFormat.setCompressOutput(job, true); job.setInt(DEFLATE_LEVEL_KEY, level); } /** Set the sync interval to be used by the underlying {@link DataFileWriter}.*/ public static void setSyncInterval(JobConf job, int syncIntervalInBytes) { job.setInt(SYNC_INTERVAL_KEY, syncIntervalInBytes); } static <T> void configureDataFileWriter(DataFileWriter<T> writer, JobConf job) throws UnsupportedEncodingException { CodecFactory factory = getCodecFactory(job); if (factory != null) { writer.setCodec(factory); } writer.setSyncInterval(job.getInt(SYNC_INTERVAL_KEY, DEFAULT_SYNC_INTERVAL)); // copy metadata from job for (Map.Entry<String, String> e : job) { if (e.getKey().startsWith(AvroJob.TEXT_PREFIX)) writer.setMeta(e.getKey().substring(AvroJob.TEXT_PREFIX.length()), e.getValue()); if (e.getKey().startsWith(AvroJob.BINARY_PREFIX)) writer.setMeta(e.getKey().substring(AvroJob.BINARY_PREFIX.length()), URLDecoder.decode(e.getValue(), "ISO-8859-1").getBytes("ISO-8859-1")); } } /** This will select the correct compression codec from the JobConf. * The order of selection is as follows: * <ul> * <li>If mapred.output.compress is true then look for codec otherwise no compression</li> * <li>Use avro.output.codec if populated</li> * <li>Next use mapred.output.compression.codec if populated</li> * <li>If not default to Deflate Codec</li> * </ul> */ static CodecFactory getCodecFactory(JobConf job) { CodecFactory factory = null; if (FileOutputFormat.getCompressOutput(job)) { int level = job.getInt(DEFLATE_LEVEL_KEY, DEFAULT_DEFLATE_LEVEL); String codecName = job.get(AvroJob.OUTPUT_CODEC); if (codecName == null) { String codecClassName = job.get("mapred.output.compression.codec", null); String avroCodecName = HadoopCodecFactory.getAvroCodecName(codecClassName); if (codecClassName != null && avroCodecName != null) { factory = HadoopCodecFactory.fromHadoopString(codecClassName); job.set(AvroJob.OUTPUT_CODEC, avroCodecName); return factory; } else { return CodecFactory.deflateCodec(level); } } else { if (codecName.equals(DEFLATE_CODEC)) { factory = CodecFactory.deflateCodec(level); } else { factory = CodecFactory.fromString(codecName); } } } return factory; } @Override public RecordWriter<AvroWrapper<T>, NullWritable> getRecordWriter(FileSystem ignore, JobConf job, String name, Progressable prog) throws IOException { boolean isMapOnly = job.getNumReduceTasks() == 0; Schema schema = isMapOnly ? AvroJob.getMapOutputSchema(job) : AvroJob.getOutputSchema(job); GenericData dataModel = AvroJob.createDataModel(job); final DataFileWriter<T> writer = new DataFileWriter<T>(dataModel.createDatumWriter(null)); configureDataFileWriter(writer, job); Path path = FileOutputFormat.getTaskOutputPath(job, name + EXT); writer.create(schema, path.getFileSystem(job).create(path)); return new RecordWriter<AvroWrapper<T>, NullWritable>() { public void write(AvroWrapper<T> wrapper, NullWritable ignore) throws IOException { writer.append(wrapper.datum()); } public void close(Reporter reporter) throws IOException { writer.close(); } }; } }