分组查找出现最多的元素hive自定义UDAF

import org.apache.hadoop.hive.ql.udf.generic.*;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.parse.SemanticException;
import org.apache.hadoop.hive.serde2.io.DoubleWritable;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorUtils;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StandardListObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StructField;
import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.DoubleObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.LongObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorUtils;
import org.apache.hadoop.hive.serde2.typeinfo.PrimitiveTypeInfo;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.util.StringUtils;
import org.apache.hadoop.hive.serde2.objectinspector.*;

import java.util.Map;
import java.util.HashMap;

@Description(name = "mostOccrItem", value = "_FUNC_(x) - Returns a object that occures most. "
 + "CAUTION will easily cause Out Of Memmory Exception on large data sets")
/**  *   * @author houzhizhen  * create temporary function mostOccrItem as com.letv.bigdata.hive.udaf.MostOccuItem  *   *    public static enum Mode {    * PARTIAL1: from original data to partial aggregation data: iterate() and  * terminatePartial() will be called.    PARTIAL1,    * PARTIAL2: from partial aggregation data to partial aggregation data:  * merge() and terminatePartial() will be called.    PARTIAL2,    * FINAL: from partial aggregation to full aggregation: merge() and  * terminate() will be called.    FINAL,    * COMPLETE: from original data directly to full aggregation: iterate() and  * terminate() will be called.    COMPLETE  };   */
public class MostOccuItem extends AbstractGenericUDAFResolver {
 static final Log LOG = LogFactory
 .getLog(MostOccuItem.class.getName());

 public MostOccuItem() {
 }

 @Override
 public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
 throws SemanticException {
 if (parameters.length != 1) {
 throw new UDFArgumentTypeException(parameters.length - 1,
 "Exactly one argument is expected.");
 }
 if (parameters[0].getCategory() != ObjectInspector.Category.PRIMITIVE) {
 throw new UDFArgumentTypeException(0,
 "Only primitive type arguments are accepted but "
 + parameters[0].getTypeName()
 + " was passed as parameter 1.");
 }
 return new GenericUDAFMkListEvaluator();
 }

 public static class GenericUDAFMkListEvaluator extends GenericUDAFEvaluator {
 // private PrimitiveObjectInspector inputOI;

 private StandardMapObjectInspector mapOI ;

 @Override
 public ObjectInspector init(Mode m, ObjectInspector[] parameters)
 throws HiveException {
 super.init(m, parameters);
 if (m == Mode.PARTIAL1 ) {
 //inputOI = (PrimitiveObjectInspector) parameters[0];
 return ObjectInspectorFactory
 .getStandardMapObjectInspector((PrimitiveObjectInspector) ObjectInspectorUtils
 .getStandardObjectInspector(PrimitiveObjectInspectorFactory.javaStringObjectInspector),PrimitiveObjectInspectorFactory.javaIntObjectInspector);
 }else if (m == Mode.PARTIAL2) {
 mapOI = (StandardMapObjectInspector) parameters[0];
 return ObjectInspectorFactory
 .getStandardMapObjectInspector(PrimitiveObjectInspectorFactory.javaStringObjectInspector,PrimitiveObjectInspectorFactory.javaIntObjectInspector);
 }else if(m == Mode.FINAL){
 mapOI = (StandardMapObjectInspector) parameters[0];
 return PrimitiveObjectInspectorFactory.javaStringObjectInspector;
 }else if(m == Mode.COMPLETE){
 return PrimitiveObjectInspectorFactory.javaStringObjectInspector;
 }else {
 throw new RuntimeException("no such mode Exception");
 }
 }

 static class MkArrayAggregationBuffer implements AggregationBuffer {
 Map<String,Integer> container;
 }

 @Override
 public void reset(AggregationBuffer agg) throws HiveException {
 ((MkArrayAggregationBuffer) agg).container = new HashMap<String,Integer>();
 }

 @Override
 public AggregationBuffer getNewAggregationBuffer() throws HiveException {
 MkArrayAggregationBuffer ret = new MkArrayAggregationBuffer();
 reset(ret);
 return ret;
 }

 // Mapside
 @Override
 public void iterate(AggregationBuffer agg, Object[] parameters)
 throws HiveException {
 assert (parameters.length == 1);
 Object p = parameters[0];

 if (p != null) {
 MkArrayAggregationBuffer myagg = (MkArrayAggregationBuffer) agg;
 putIntoMap(p.toString(), myagg, 1);
 }
 }

 // Mapside
 @Override
 public Object terminatePartial(AggregationBuffer agg)
 throws HiveException {
 MkArrayAggregationBuffer myagg = (MkArrayAggregationBuffer) agg;
 Map<String,Integer> ret = new HashMap<String,Integer>(
 myagg.container);
 
 return ret;
 }

 @Override
 public void merge(AggregationBuffer agg, Object partial)
 throws HiveException {
 MkArrayAggregationBuffer myagg = (MkArrayAggregationBuffer) agg;
 
 Map partialResult = mapOI.getMap(partial) ;
 
 for(Object key : partialResult.keySet()){
 
 putIntoMap(key.toString(),myagg,Integer.valueOf(partialResult.get(key).toString()) );
 }
 }

 @Override
 public String terminate(AggregationBuffer agg) throws HiveException {
 Map<Object,Integer> map = new HashMap<Object,Integer>();
 MkArrayAggregationBuffer myagg = (MkArrayAggregationBuffer) agg;
 int num = Integer.MIN_VALUE;
 String key = null;
 for(Map.Entry<String,Integer> entry :myagg.container.entrySet()){
 if(num < entry.getValue()) {
 num = entry.getValue();
 key = entry.getKey();
 }
 }
 return key;
 }
 
 private void putIntoMap(String p, MkArrayAggregationBuffer myagg,int num) {
 // Object pCopy = ObjectInspectorUtils.copyToStandardObject(p,this.inputOI);
 Integer i = myagg.container.get(p);
 if(i==null) {
 i = num;
 }else{
 i = i + num;
 }
 myagg.container.put(p, i);
 }
 }
}