/**
 * Responsible for dynamically determining a @{link PartitionKey}.
 *
 * @param <K> Type of key
 * @param <V> Type of value
 */
public abstract class DynamicPartitioner<K, V> {


  /**
   *  Initializes a DynamicPartitioner.
   *  <p>
   *    This method will be called only once per {@link DynamicPartitioner} instance. It is the first method call
        on that instance.
   *  </p>
   *  @param logicalStartTime see {@link co.cask.cdap.api.mapreduce.MapReduceContext#getLogicalStartTime}
   *
   */
  public void initialize(long logicalStartTime) {
    // do nothing be default
  }


  /**
   *  Destroys a DynamicPartitioner.
   *  <p>
   *    This method will be called only once per {@link DynamicPartitioner} instance. It is the last method call
   *    on that instance.
   *  </p>
   */
  public void destroy() {
    // do nothing by default
  }

  /**
   * Determine the PartitionKey for the key-value pair to be written to.
   *
   * @param key the key to be written
   * @param value the value to be written
   * @return the {@link PartitionKey} for the key-value pair to be written to.
   */
  public abstract PartitionKey getPartitionKey(K key, V value);
}

public static final class CustomDynamicPartitioner extends DynamicPartitioner<byte[], Long> {
  private long logicalStartTime;

  @Override
  public void initialize(long logicalStartTime) {
    this.logicalStartTime = logicalStartTime;
  }

  @Override
  public PartitionKey getPartitionKey(byte[] key, Long value) {
    return PartitionKey.builder().addLongField("time", logicalStartTime).addLongField("other", value).build();
  }
}

public void beforeSubmit(MapReduceContext context) throws Exception {
  // define input and other setup
  // ...

  Map<String, String> outputArgs = new HashMap<>();
  // alternative to setting the PartitionKey, set a DynamicPartitioner class
  PartitionedFileSetArguments.setDynamicPartitioner(outputArgs, CustomDynamicPartitioner.class);
  context.addOutput("outputLines", outputArgs);
}