ValueAggregatorCombiner.java 文件源码

/** Combines values for a given key.  
 * @param key the key is expected to be a Text object, whose prefix indicates
 * the type of aggregation to aggregate the values. 
 * @param values the values to combine
 * @param context to collect combined values
 */
public void reduce(Text key, Iterable<Text> values, Context context) 
    throws IOException, InterruptedException {
  String keyStr = key.toString();
  int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR);
  String type = keyStr.substring(0, pos);
  long uniqCount = context.getConfiguration().
    getLong(UniqValueCount.MAX_NUM_UNIQUE_VALUES, Long.MAX_VALUE);
  ValueAggregator aggregator = ValueAggregatorBaseDescriptor
    .generateValueAggregator(type, uniqCount);
  for (Text val : values) {
    aggregator.addNextValue(val);
  }
  Iterator<?> outputs = aggregator.getCombinerOutput().iterator();

  while (outputs.hasNext()) {
    Object v = outputs.next();
    if (v instanceof Text) {
      context.write(key, (Text)v);
    } else {
      context.write(key, new Text(v.toString()));
    }
  }
}