Hive UDAF开发

Hive进行UDAF开发，相对要比UDF复杂一些，不过也不是很难。

请看一个例子

package org.hrj.hive.udf;

import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;
import org.apache.hadoop.hive.serde2.io.DoubleWritable;



public class UDAFSum_Sample extends NumericUDAF {
         public static class Evaluator implements UDAFEvaluator {
                 private boolean mEmpty;
                 private double mSum;
                 public Evaluator() {
                         super();
                        init();
                }

                 public void init() {
                        mSum = 0;
                        mEmpty = true;
                }

                 public boolean iterate(DoubleWritable o) {
                         if (o != null) {
                                mSum += o.get();
                                mEmpty = false;
                        }
                         return true;
                }

                 public DoubleWritable terminatePartial() {
                         // This is SQL standard - sum of zero items should be null.
                         return mEmpty ? null : new DoubleWritable(mSum);
                }

                 public boolean merge(DoubleWritable o) {
                         if (o != null) {
                                mSum += o.get();
                                mEmpty = false;
                        }
                         return true;
                }

                 public DoubleWritable terminate() {
                         // This is SQL standard - sum of zero items should be null.
                         return mEmpty ? null : new DoubleWritable(mSum);
                }
        }
}

1. 将java文件编译成Sum_Sample.jar
2. 进入hive

hive> add jar Sum_sample.jar;

hive> create temporary function sum_test as 'com.hrj.hive.udf.UDAFSum_Sample';

hive> select sum_test(t.num) from t;

hive> drop temporary function sum_test;

hive> quit;

关于UDAF开发注意点：

1. 需要import org.apache.hadoop.hive.ql.exec.UDAF以及org.apache.hadoop.hive.ql.exec.UDAFEvaluator,这两个包都是必须的
2. 函数类需要继承UDAF类，内部类Evaluator实现UDAFEvaluator接口
3. Evaluator需要实现 init、iterate、terminatePartial、merge、terminate这几个函数
1. init函数类似于构造函数，用于UDAF的初始化
2. iterate接收传入的参数，并进行内部的轮转。其返回类型为boolean
3. terminatePartial无参数，其为iterate函数轮转结束后，返回乱转数据，iterate和terminatePartial类似于hadoop的Combiner
4. merge接收terminatePartial的返回结果，进行数据merge操作，其返回类型为boolean
5. terminate返回最终的聚集函数结果