Java编写UDAF

小鱼儿 2022-06-09 14:17 201阅读 0赞

转载自：http://blog.csdn.net/genghaihua/article/details/43483807

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