Chain.java 文件源码

/**
 * 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;
}