Hadoop基础教程-第12章 Hive：进阶（12.2 自定义函数）（草稿）

第12章 Hive：进阶

12.2 自定义函数

12.2.1 UDP

使用Eclipse编写UDP函数，可以通过maven下载需要的jar包，pom.xml文件如下。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0</modelVersion>    <groupId>cn.hadron</groupId>    <artifactId>hiveFun</artifactId>    <version>0.0.1-SNAPSHOT</version>    <packaging>jar</packaging>    <name>hiveFun</name>    <url>http://maven.apache.org</url>    <properties>        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>    </properties>    <dependencies>        <dependency>            <groupId>junit</groupId>            <artifactId>junit</artifactId>            <version>3.8.1</version>            <scope>test</scope>        </dependency>        <!-- https://mvnrepository.com/artifact/org.apache.hive/hive-exec -->        <dependency>            <groupId>org.apache.hive</groupId>            <artifactId>hive-exec</artifactId>            <version>2.1.1</version>        </dependency>        <dependency>            <groupId>jdk.tools</groupId>            <artifactId>jdk.tools</artifactId>            <version>1.8</version>            <scope>system</scope>            <systemPath>${JAVA_HOME}/lib/tools.jar</systemPath>        </dependency>    </dependencies>    <repositories>    <repository>      <id>central</id>      <name>Central Repository</name>      <url>http://maven.aliyun.com/nexus/content/repositories/central</url>      <layout>default</layout>      <snapshots>        <enabled>false</enabled>      </snapshots>    </repository>  </repositories></project>

package cn.hadron.hiveFun;import org.apache.hadoop.hive.ql.exec.UDF;import org.apache.hadoop.io.Text;import org.apache.hadoop.io.DoubleWritable;public class LevelUDF extends UDF{     public Text evaluate(double sal){         if(sal<1500){             return new Text("穷人");         }else if(sal<2000){             return new Text("温饱");         }else if(sal<3000){             return new Text("低产");         }else if(sal<6000){             return new Text("中产");         }else if(sal<8000){             return new Text("高产");         }else{             return new Text("富人");         }     }}

导出jar包

hive> add jar /root/hiveFun.jar;Added [/root/hiveFun.jar] to class pathAdded resources: [/root/hiveFun.jar]hive> create temporary function level_sal as 'cn.hadron.hiveFun.LevelUDF';OKTime taken: 1.06 secondshive>

hive> select ename,level_sal(sal) from emp;OKCLARK   低产KING    中产MILLER  穷人SMITH   穷人JONES   低产FORD    中产ALLEN   温饱WARD    穷人MARTIN  穷人BLAKE   低产TURNER  温饱JAMES   穷人HADRON  高产Time taken: 0.181 seconds, Fetched: 13 row(s)hive> 

12.2.2 UDAF

UDAF是用户自定义聚合函数。
要实现UDAF，我们需要实现下面的类：
org.apache.hadoop.hive.ql.udf.generic.AbstractGenericUDAFResolver
org.apache.hadoop.hive.ql.udf.generic.GenericUDAFEvaluator
AbstractGenericUDAFResolver检查输入参数，并且指定使用哪个resolver。

GenericUDAFResolver类已经过时弃用了，现在是实现GenericUDAFResolver2接口