Chain.java 文件源码

/**
 * Creates a {@link Configuration} for the Map or Reduce in the chain.
 * 
 * <p>
 * It creates a new Configuration using the chain job's Configuration as base
 * and adds to it the configuration properties for the chain element. The keys
 * of the chain element Configuration have precedence over the given
 * Configuration.
 * </p>
 * 
 * @param jobConf
 *          the chain job's Configuration.
 * @param confKey
 *          the key for chain element configuration serialized in the chain
 *          job's Configuration.
 * @return a new Configuration aggregating the chain job's Configuration with
 *         the chain element configuration properties.
 */
protected static Configuration getChainElementConf(Configuration jobConf,
    String confKey) {
  Configuration conf = null;
  try {
    Stringifier<Configuration> stringifier = 
      new DefaultStringifier<Configuration>(jobConf, Configuration.class);
    String confString = jobConf.get(confKey, null);
    if (confString != null) {
      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 a
  // new Configuration(jobConf) in the creation of the conf above
  jobConf = new Configuration(jobConf);

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