/**
 * Creates a {@link JobConf} for one of the Maps or Reduce in the chain.
 * <p/>
 * It creates a new JobConf using the chain job's JobConf as base and adds to
 * it the configuration properties for the chain element. The keys of the
 * chain element jobConf have precedence over the given JobConf.
 *
 * @param jobConf the chain job's JobConf.
 * @param confKey the key for chain element configuration serialized in the
 *                chain job's JobConf.
 * @return a new JobConf aggregating the chain job's JobConf with the chain
 *         element configuration properties.
 */
private static JobConf getChainElementConf(JobConf jobConf, String confKey) {
  JobConf conf;
  try {
    Stringifier<JobConf> stringifier =
      new DefaultStringifier<JobConf>(jobConf, JobConf.class);
    conf = stringifier.fromString(jobConf.get(confKey, null));
  } catch (IOException ioex) {
    throw new RuntimeException(ioex);
  }
  // we have to do this because the Writable desearialization clears all
  // values set in the conf making not possible do do a new JobConf(jobConf)
  // in the creation of the conf above
  jobConf = new JobConf(jobConf);

  for(Map.Entry<String, String> entry : conf) {
    jobConf.set(entry.getKey(), entry.getValue());
  }
  return jobConf;
}
 

/**
 * Creates a {@link JobConf} for one of the Maps or Reduce in the chain.
 * <p/>
 * It creates a new JobConf using the chain job's JobConf as base and adds to
 * it the configuration properties for the chain element. The keys of the
 * chain element jobConf have precedence over the given JobConf.
 *
 * @param jobConf the chain job's JobConf.
 * @param confKey the key for chain element configuration serialized in the
 *                chain job's JobConf.
 * @return a new JobConf aggregating the chain job's JobConf with the chain
 *         element configuration properties.
 */
private static JobConf getChainElementConf(JobConf jobConf, String confKey) {
  JobConf conf;
  try {
    Stringifier<JobConf> stringifier =
      new DefaultStringifier<JobConf>(jobConf, JobConf.class);
    conf = stringifier.fromString(jobConf.get(confKey, null));
  } catch (IOException ioex) {
    throw new RuntimeException(ioex);
  }
  // we have to do this because the Writable desearialization clears all
  // values set in the conf making not possible do do a new JobConf(jobConf)
  // in the creation of the conf above
  jobConf = new JobConf(jobConf);

  for(Map.Entry<String, String> entry : conf) {
    jobConf.set(entry.getKey(), entry.getValue());
  }
  return jobConf;
}
 

/**
 * Sets the Reducer class to the chain job's JobConf.
 * <p/>
 * The configuration properties of the chain job have precedence over the
 * configuration properties of the Reducer.
 *
 * @param jobConf              chain job's JobConf to add the Reducer class.
 * @param klass            the Reducer class to add.
 * @param inputKeyClass    reducer input key class.
 * @param inputValueClass  reducer input value class.
 * @param outputKeyClass   reducer output key class.
 * @param outputValueClass reducer output value class.
 * @param byValue          indicates if key/values should be passed by value
 * to the next Mapper in the chain, if any.
 * @param reducerConf      a JobConf with the configuration for the Reducer
 * class. It is recommended to use a JobConf without default values using the
 * <code>JobConf(boolean loadDefaults)</code> constructor with FALSE.
 */
public static <K1, V1, K2, V2> void setReducer(JobConf jobConf,
                        Class<? extends Reducer<K1, V1, K2, V2>> klass,
                        Class<? extends K1> inputKeyClass,
                        Class<? extends V1> inputValueClass,
                        Class<? extends K2> outputKeyClass,
                        Class<? extends V2> outputValueClass,
                        boolean byValue, JobConf reducerConf) {
  String prefix = getPrefix(false);

  if (jobConf.getClass(prefix + CHAIN_REDUCER_CLASS, null) != null) {
    throw new IllegalStateException("Reducer has been already set");
  }

  jobConf.setClass(prefix + CHAIN_REDUCER_CLASS, klass, Reducer.class);

  // if the Reducer does not have a private JobConf create an empty one
  if (reducerConf == null) {
    // using a JobConf without defaults to make it lightweight.
    // still the chain JobConf may have all defaults and this conf is
    // overlapped to the chain JobConf one.
    reducerConf = new JobConf(false);
  }

  // store in the private reducer conf the input/output classes of the reducer
  // and if it works by value or by reference
  reducerConf.setBoolean(MAPPER_BY_VALUE, byValue);
  reducerConf.setClass(REDUCER_INPUT_KEY_CLASS, inputKeyClass, Object.class);
  reducerConf.setClass(REDUCER_INPUT_VALUE_CLASS, inputValueClass,
                       Object.class);
  reducerConf.setClass(REDUCER_OUTPUT_KEY_CLASS, outputKeyClass,
                       Object.class);
  reducerConf.setClass(REDUCER_OUTPUT_VALUE_CLASS, outputValueClass,
                       Object.class);

  // serialize the private mapper jobconf in the chain jobconf.
  Stringifier<JobConf> stringifier =
    new DefaultStringifier<JobConf>(jobConf, JobConf.class);
  try {
    jobConf.set(prefix + CHAIN_REDUCER_CONFIG,
                stringifier.toString(new JobConf(reducerConf)));
  }
  catch (IOException ioEx) {
    throw new RuntimeException(ioEx);
  }
}
 

/**
 * Sets the Reducer class to the chain job's JobConf.
 * <p/>
 * The configuration properties of the chain job have precedence over the
 * configuration properties of the Reducer.
 *
 * @param jobConf              chain job's JobConf to add the Reducer class.
 * @param klass            the Reducer class to add.
 * @param inputKeyClass    reducer input key class.
 * @param inputValueClass  reducer input value class.
 * @param outputKeyClass   reducer output key class.
 * @param outputValueClass reducer output value class.
 * @param byValue          indicates if key/values should be passed by value
 * to the next Mapper in the chain, if any.
 * @param reducerConf      a JobConf with the configuration for the Reducer
 * class. It is recommended to use a JobConf without default values using the
 * <code>JobConf(boolean loadDefaults)</code> constructor with FALSE.
 */
public static <K1, V1, K2, V2> void setReducer(JobConf jobConf,
                        Class<? extends Reducer<K1, V1, K2, V2>> klass,
                        Class<? extends K1> inputKeyClass,
                        Class<? extends V1> inputValueClass,
                        Class<? extends K2> outputKeyClass,
                        Class<? extends V2> outputValueClass,
                        boolean byValue, JobConf reducerConf) {
  String prefix = getPrefix(false);

  if (jobConf.getClass(prefix + CHAIN_REDUCER_CLASS, null) != null) {
    throw new IllegalStateException("Reducer has been already set");
  }

  jobConf.setClass(prefix + CHAIN_REDUCER_CLASS, klass, Reducer.class);

  // if the Reducer does not have a private JobConf create an empty one
  if (reducerConf == null) {
    // using a JobConf without defaults to make it lightweight.
    // still the chain JobConf may have all defaults and this conf is
    // overlapped to the chain JobConf one.
    reducerConf = new JobConf(false);
  }

  // store in the private reducer conf the input/output classes of the reducer
  // and if it works by value or by reference
  reducerConf.setBoolean(MAPPER_BY_VALUE, byValue);
  reducerConf.setClass(REDUCER_INPUT_KEY_CLASS, inputKeyClass, Object.class);
  reducerConf.setClass(REDUCER_INPUT_VALUE_CLASS, inputValueClass,
                       Object.class);
  reducerConf.setClass(REDUCER_OUTPUT_KEY_CLASS, outputKeyClass,
                       Object.class);
  reducerConf.setClass(REDUCER_OUTPUT_VALUE_CLASS, outputValueClass,
                       Object.class);

  // serialize the private mapper jobconf in the chain jobconf.
  Stringifier<JobConf> stringifier =
    new DefaultStringifier<JobConf>(jobConf, JobConf.class);
  try {
    jobConf.set(prefix + CHAIN_REDUCER_CONFIG,
                stringifier.toString(new JobConf(reducerConf)));
  }
  catch (IOException ioEx) {
    throw new RuntimeException(ioEx);
  }
}