DelegatingMapper.java

/**
 * 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.input;

import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.util.ReflectionUtils;

/**
 * An {@link Mapper} that delegates behavior of paths to multiple other
 * mappers.
 * 
 * @see MultipleInputs#addInputPath(Job, Path, Class, Class)
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class DelegatingMapper<K1, V1, K2, V2> extends Mapper<K1, V1, K2, V2> {

  private Mapper<K1, V1, K2, V2> mapper;

  @SuppressWarnings("unchecked")
  protected void setup(Context context)
      throws IOException, InterruptedException {
    // Find the Mapper from the TaggedInputSplit.
    TaggedInputSplit inputSplit = (TaggedInputSplit) context.getInputSplit();
    mapper = (Mapper<K1, V1, K2, V2>) ReflectionUtils.newInstance(inputSplit
       .getMapperClass(), context.getConfiguration());
    
  }

  @SuppressWarnings("unchecked")
  public void run(Context context) 
      throws IOException, InterruptedException {
    setup(context);
    mapper.run(context);
    cleanup(context);
  }
}