UDTFExplodeMap.java

package com.facebook.hive.udf;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDTF;
import org.apache.hadoop.hive.serde2.objectinspector.MapObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;

import java.util.ArrayList;
import java.util.Map;

/**
 * GenericUDTFExplodeMap.
 *
 */
@Description(name = "explode_map",
             value = "_FUNC_(a) - separates the elements of map a into multiple rows ")
public class UDTFExplodeMap extends GenericUDTF {

  private MapObjectInspector mapOI = null;

  @Override
  public void close() throws HiveException {
  }

  @Override
  public StructObjectInspector initialize(ObjectInspector[] args) throws UDFArgumentException {
    if (args.length != 1) {
      throw new UDFArgumentException("explode_map() takes only one argument");
    }

    if (args[0].getCategory() != ObjectInspector.Category.MAP) {
      throw new UDFArgumentException("explode_map() takes a map as a parameter");
    }
    mapOI = (MapObjectInspector) args[0];

    ArrayList<String> fieldNames = new ArrayList<String>();
    ArrayList<ObjectInspector> fieldOIs = new ArrayList<ObjectInspector>();
    fieldNames.add("col1");
    fieldNames.add("col2");
    fieldOIs.add(mapOI.getMapKeyObjectInspector());
    fieldOIs.add(mapOI.getMapValueObjectInspector());
    return ObjectInspectorFactory.getStandardStructObjectInspector(fieldNames,
                                                                   fieldOIs);
  }

  private final Object[] forwardObj = new Object[2];

  @Override
  public void process(Object[] o) throws HiveException {
    Map<?, ?> map = mapOI.getMap(o[0]);
    if (map == null) {
      return;
    }
    for (Map.Entry entry : map.entrySet()) {
      forwardObj[0] = entry.getKey();
      forwardObj[1] = entry.getValue();
      forward(forwardObj);
    }
  }

  @Override
  public String toString() {
    return "explode_map";
  }
}