org.apache.hadoop.mapreduce.lib.output.LazyOutputFormat.java Source code

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Here is the source code for org.apache.hadoop.mapreduce.lib.output.LazyOutputFormat.java

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/**
 * 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.hadoop.mapreduce.lib.output;

import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
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.util.ReflectionUtils;

/**
 * A Convenience class that creates output lazily.
 * Use in conjuction with org.apache.hadoop.mapreduce.lib.output.MultipleOutputs to recreate the
 * behaviour of org.apache.hadoop.mapred.lib.MultipleTextOutputFormat (etc) of the old Hadoop API.
 * See {@link MultipleOutputs} documentation for more information.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class LazyOutputFormat<K, V> extends FilterOutputFormat<K, V> {
    public static String OUTPUT_FORMAT = "mapreduce.output.lazyoutputformat.outputformat";

    /**
     * Set the underlying output format for LazyOutputFormat.
     * @param job the {@link Job} to modify
     * @param theClass the underlying class
     */
    @SuppressWarnings("unchecked")
    public static void setOutputFormatClass(Job job, Class<? extends OutputFormat> theClass) {
        job.setOutputFormatClass(LazyOutputFormat.class);
        job.getConfiguration().setClass(OUTPUT_FORMAT, theClass, OutputFormat.class);
    }

    @SuppressWarnings("unchecked")
    private void getBaseOutputFormat(Configuration conf) throws IOException {
        baseOut = ((OutputFormat<K, V>) ReflectionUtils.newInstance(conf.getClass(OUTPUT_FORMAT, null), conf));
        if (baseOut == null) {
            throw new IOException("Output Format not set for LazyOutputFormat");
        }
    }

    @Override
    public RecordWriter<K, V> getRecordWriter(TaskAttemptContext context) throws IOException, InterruptedException {
        if (baseOut == null) {
            getBaseOutputFormat(context.getConfiguration());
        }
        return new LazyRecordWriter<K, V>(baseOut, context);
    }

    @Override
    public void checkOutputSpecs(JobContext context) throws IOException, InterruptedException {
        if (baseOut == null) {
            getBaseOutputFormat(context.getConfiguration());
        }
        super.checkOutputSpecs(context);
    }

    @Override
    public OutputCommitter getOutputCommitter(TaskAttemptContext context) throws IOException, InterruptedException {
        if (baseOut == null) {
            getBaseOutputFormat(context.getConfiguration());
        }
        return super.getOutputCommitter(context);
    }

    /**
     * A convenience class to be used with LazyOutputFormat
     */
    private static class LazyRecordWriter<K, V> extends FilterRecordWriter<K, V> {

        final OutputFormat<K, V> outputFormat;
        final TaskAttemptContext taskContext;

        public LazyRecordWriter(OutputFormat<K, V> out, TaskAttemptContext taskContext)
                throws IOException, InterruptedException {
            this.outputFormat = out;
            this.taskContext = taskContext;
        }

        @Override
        public void write(K key, V value) throws IOException, InterruptedException {
            if (rawWriter == null) {
                rawWriter = outputFormat.getRecordWriter(taskContext);
            }
            rawWriter.write(key, value);
        }

        @Override
        public void close(TaskAttemptContext context) throws IOException, InterruptedException {
            if (rawWriter != null) {
                rawWriter.close(context);
            }
        }

    }
}