Hive 自定义函数编程

Hive 自定义函数编程

Hive中的自定义函数简介

(1) 在类中创建自定义函数。自定义UDF需要继承'org.apache.hadoop.hive.ql.exec.UDF',实现evaluate函数,evaluate函数支持重载。

package demo.udf;

import org.apache.hadoop.hive.ql.exec.UDF;

import org.apache.hadoop.io.Text;

public class ConcatString extends UDF {

// string can not translation in hadoop

public Text evaluate(Text a, Text b) {

    return new Text(a.toString() + "*******" + b.toString());

}

}

(2) 将该类所在的包导出成jar包，放入linux目录下。如 jar包名为 concatstring.jar

(3) 进入hive客户端，删除旧的jar包

hive> delete jar /dir/concatstring.jar;

(4) 添加新的jar包

hive> add jar /dir/concatstring.jar

(5) 创建临时函数，指向jar包中的类:.语法  create temporary function <函数名> as 'java类名';

hive> create temporary function myconcat as 'demo.udf.ConcatString';

(6) 使用临时函数

select myconcat (''Hello','World');

drop temporary function  myconcat;

hive> delete jar /root/pl62716/hive/contactString.jar;

Deleted [/root/pl62716/hive/contactString.jar] from class path

hive> add jar /root/pl62716/hive/contactString.jar;

Added [/root/pl62716/hive/contactString.jar] to class path

Added resources: [/root/pl62716/hive/contactString.jar]

hive> create temporary function myconcat as 'demo.udf.ConcatString';

OK

Time taken: 2.747 seconds

hive> select myconcat('HELLO','world');

OK

Hello*******world

Time taken: 0.598 seconds, Fetched: 1 row(s