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当Hive提供的内置函数不能满足查询需求时，用户可以根据自己业务编写自定义函数（User Defined Functions, UDF), 然后在HiveQL中调用。

例如有这样一个需求：为了保护用户隐私，当查询数据的时候，需要将用户手机号的中间四位用*号代替，比如手机号18001292688需要显示为180****2688。这时候就可以写一个自定义函数实现这个需求。

新建项目MyUDF,添加Maven依赖

<?xml version="1.0" encoding="UTF-8"?>
<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>org.example</groupId><artifactId>MyUDF</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><hive.version>2.1.1-cdh6.1.0</hive.version></properties><dependencies><dependency><groupId>jdk.tools</groupId><artifactId>jdk.tools</artifactId><version>1.8</version><scope>system</scope><systemPath>${JAVA_HOME}/lib/tools.jar</systemPath></dependency><!--Hadoop common包--><!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-common --><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-common</artifactId><version>2.10.2</version></dependency><!-- https://mvnrepository.com/artifact/org.apache.hive/hive-exec --><dependency><groupId>org.apache.hive</groupId><artifactId>hive-exec</artifactId><version>${hive.version}</version></dependency></dependencies><!--添加CDH的仓库--><repositories><repository><id>nexus-aliyun</id><url>http://maven.aliyun.com/nexus/content/groups/public</url></repository><repository><id>cloudera</id><url>https://repository.cloudera.com/artifactory/cloudera-repos</url></repository></repositories><build><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.6.0</version><configuration><source>1.8</source><target>1.8</target><encoding>UTF-8</encoding></configuration></plugin></plugins></build></project>

新建类hive.demo.MyUDF

package hive.demo;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.Text;/*** Hive自定义函数类*/
public class MyUDF extends UDF{/*** @param text* 调用函数时需要传入的参数* @return 隐藏后的手机号码* 自定义函数类需要一个名为evaluate()的方法，Hive将调用该方法*/public String evaluate(Text text){String result = "手机号码错误！";if(text != null && text.getLength() == 11){String inputStr = text.toString();StringBuffer sb = new StringBuffer();sb.append(inputStr.substring(0,3));sb.append("****");sb.append(inputStr.substring(7));result = sb.toString();}return result;}
}

 打包MyUDF.jar上传至路径，比如/home/hadoop/

在Hive CLI中执行

hive>add jar /home/hadoop/MyUDF.jar;

创建函数名称

CREATE TEMPORARY FUNCTION formatPhone AS 'hive.demo.MyUDF';

新建一个表测试一下这个自定义的函数

CREATE TABLE t_user(id INT, phone STRING);
INSERT INTO TABLE t_user 
SELECT 1, '13123567589'
UNION ALL SELECT 2, '15898705673'
UNION ALL SELECT 3, '18001292688';