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    
019    package org.apache.hadoop.mapred.lib;
020    
021    import java.io.IOException;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    import org.apache.hadoop.fs.FileSystem;
026    import org.apache.hadoop.mapred.JobConf;
027    import org.apache.hadoop.mapred.OutputFormat;
028    import org.apache.hadoop.mapred.RecordWriter;
029    import org.apache.hadoop.mapred.Reporter;
030    import org.apache.hadoop.util.Progressable;
031    import org.apache.hadoop.util.ReflectionUtils;
032    
033    /**
034     * A Convenience class that creates output lazily. 
035     */
036    @InterfaceAudience.Public
037    @InterfaceStability.Stable
038    public class LazyOutputFormat<K, V> extends FilterOutputFormat<K, V> {
039      /**
040       * Set the underlying output format for LazyOutputFormat.
041       * @param job the {@link JobConf} to modify
042       * @param theClass the underlying class
043       */
044      @SuppressWarnings("unchecked")
045      public static void  setOutputFormatClass(JobConf job, 
046          Class<? extends OutputFormat> theClass) {
047          job.setOutputFormat(LazyOutputFormat.class);
048          job.setClass("mapreduce.output.lazyoutputformat.outputformat", theClass, OutputFormat.class);
049      }
050    
051      @Override
052      public RecordWriter<K, V> getRecordWriter(FileSystem ignored, JobConf job, 
053          String name, Progressable progress) throws IOException {
054        if (baseOut == null) {
055          getBaseOutputFormat(job);
056        }
057        return new LazyRecordWriter<K, V>(job, baseOut, name, progress);
058      }
059    
060      @Override
061      public void checkOutputSpecs(FileSystem ignored, JobConf job) 
062      throws IOException {
063        if (baseOut == null) {
064          getBaseOutputFormat(job);
065        }
066        super.checkOutputSpecs(ignored, job);
067      }
068    
069      @SuppressWarnings("unchecked")
070      private void getBaseOutputFormat(JobConf job) throws IOException {
071        baseOut = ReflectionUtils.newInstance(
072            job.getClass("mapreduce.output.lazyoutputformat.outputformat", null, OutputFormat.class), 
073            job); 
074        if (baseOut == null) {
075          throw new IOException("Ouput format not set for LazyOutputFormat");
076        }
077      }
078      
079      /**
080       * <code>LazyRecordWriter</code> is a convenience 
081       * class that works with LazyOutputFormat.
082       */
083    
084      private static class LazyRecordWriter<K,V> extends FilterRecordWriter<K,V> {
085    
086        final OutputFormat of;
087        final String name;
088        final Progressable progress;
089        final JobConf job;
090    
091        public LazyRecordWriter(JobConf job, OutputFormat of, String name,
092            Progressable progress)  throws IOException {
093          this.of = of;
094          this.job = job;
095          this.name = name;
096          this.progress = progress;
097        }
098    
099        @Override
100        public void close(Reporter reporter) throws IOException {
101          if (rawWriter != null) {
102            rawWriter.close(reporter);
103          }
104        }
105    
106        @Override
107        public void write(K key, V value) throws IOException {
108          if (rawWriter == null) {
109            createRecordWriter();
110          }
111          super.write(key, value);
112        }
113    
114        @SuppressWarnings("unchecked")
115        private void createRecordWriter() throws IOException {
116          FileSystem fs = FileSystem.get(job);
117          rawWriter = of.getRecordWriter(fs, job, name, progress);
118        }  
119      }
120    }