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Apache Hadoop MapReduce Streaming

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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.streaming.io;

import java.io.DataInput;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.streaming.PipeMapRed;
import org.apache.hadoop.util.LineReader;

/**
 * OutputReader that reads the client's output as text, interpreting each line
 * as a key and outputting NullWritables for values.
 */
public class KeyOnlyTextOutputReader extends OutputReader {

  private LineReader lineReader;
  private byte[] bytes;
  private DataInput clientIn;
  private Configuration conf;
  private Text key;
  private Text line;
  
  @Override
  public void initialize(PipeMapRed pipeMapRed) throws IOException {
    super.initialize(pipeMapRed);
    clientIn = pipeMapRed.getClientInput();
    conf = pipeMapRed.getConfiguration();
    lineReader = new LineReader((InputStream)clientIn, conf);
    key = new Text();
    line = new Text();
  }
  
  @Override
  public boolean readKeyValue() throws IOException {
    if (lineReader.readLine(line) <= 0) {
      return false;
    }
    bytes = line.getBytes();
    key.set(bytes, 0, line.getLength());

    line.clear();
    return true;
  }
  
  @Override
  public Text getCurrentKey() throws IOException {
    return key;
  }
  
  @Override
  public NullWritable getCurrentValue() throws IOException {
    return NullWritable.get();
  }

  @Override
  public String getLastOutput() {
    if (bytes != null) {
      try {
        return new String(bytes, "UTF-8");
      } catch (UnsupportedEncodingException e) {
        return "";
      }
    } else {
      return null;
    }
  }
  
}