UDAFTest

package com.XX.udf;

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.ql.udf.generic.AbstractGenericUDAFResolver;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDAFEvaluator;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;
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.TypeInfo;
import org.apache.hadoop.io.LongWritable;

public class UDAFTest extends AbstractGenericUDAFResolver{
    //判断
    @Override
    public GenericUDAFEvaluator getEvaluator(TypeInfo[] info)//字段的描述信息参数parameters
            throws SemanticException {
        if(info.length !=2){
            throw new UDFArgumentTypeException(info.length-1,
                    "Exactly two argument is expected.");
        }

        //返回处理逻辑的类
        return new GenericEvaluate();
    }

    public static class GenericEvaluate extends GenericUDAFEvaluator{

        private LongWritable result;
        private PrimitiveObjectInspector inputIO1;
        private PrimitiveObjectInspector inputIO2;

        //这个方法map与reduce阶段都需要执行
        /**
         * map阶段：parameters长度与udaf输入的参数个数有关
         * reduce阶段：parameters长度为1
         */
        //初始化
        @Override
        public ObjectInspector init(Mode m, ObjectInspector[] parameters)
                throws HiveException {
            super.init(m, parameters);

            //返回最终的结果
            result = new LongWritable(0);

            inputIO1 = (PrimitiveObjectInspector) parameters[0];
            if (parameters.length>1) {
                inputIO2 = (PrimitiveObjectInspector) parameters[1];
            }

            return PrimitiveObjectInspectorFactory.writableBinaryObjectInspector;
        }

        //map阶段  iterate函数处理读入的行数据
        @Override
        public void iterate(AggregationBuffer agg, Object[] parameters)//agg缓存结果值
                throws HiveException {

            assert(parameters.length==2);

            if(parameters==null || parameters[0]==null ||  parameters[1]==null){
                return;
            }

            double base = PrimitiveObjectInspectorUtils.getDouble(parameters[0], inputIO1);
            double tmp = PrimitiveObjectInspectorUtils.getDouble(parameters[1], inputIO2);

            if(base > tmp){
                ((CountAgg)agg).count++;
            }
        }

        //获得一个聚合的缓冲对象，每个map执行一次
        @Override
        public AggregationBuffer getNewAggregationBuffer() throws HiveException {

            CountAgg agg = new CountAgg();

            reset(agg);

            return agg;
        }

        //自定义类用于计数
        public static class CountAgg implements AggregationBuffer{
            long count;//计数，保存每次临时的结果
        }

        //重置
        @Override
        public void reset(AggregationBuffer countagg) throws HiveException {
            CountAgg agg = (CountAgg)countagg;
            agg.count=0;
        }

        //该方法当做iterate执行后，部分结果返回。  terminatePartial 返回iterate处理的中间结果
        @Override
        public Object terminatePartial(AggregationBuffer agg)
                throws HiveException {

            result.set(((CountAgg)agg).count);

            return result;
        }



        @Override    //合并处理结果
        public void merge(AggregationBuffer agg, Object partial)
                throws HiveException {
            if(partial != null){
                long p = PrimitiveObjectInspectorUtils.getLong(partial, inputIO1);
                ((CountAgg)agg).count += p;
            }
        }

        @Override  //返回最终值
        public Object terminate(AggregationBuffer agg) throws HiveException {
            result.set(((CountAgg)agg).count);
            return result;
        }
    }
}