Hive3详细教程（九）Hive3自定义UDF函数（IDEA Maven版）

因为Hive本身是Java开发的，所以我们可以使用Java定义函数供Hive SQL使用。
我们通过定义一个将输入字符串转换成反向输出的案例来探究UDF函数的自定义。
在idea中使用maven开发，项目结构如下：

pom.xml:

<?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">
    <parent>
        <artifactId>bigdata</artifactId>
        <groupId>com.alan</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>testHive</artifactId>

    <name>testHive</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.apache.hive/hive-exec -->
        <dependency>
            <groupId>org.apache.hive</groupId>
            <artifactId>hive-exec</artifactId>
            <version>3.1.2</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-common -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>3.3.1</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>com.alan.WordCountDriver</mainClass>
                        </manifest>
                    </archive>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id> <!-- this is used for inheritance merges -->
                        <phase>package</phase> <!-- bind to the packaging phase -->
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

实现一个字符串的反转输出：

Java代码：

package com.alan;

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

@SuppressWarnings("deprecation")
public class RevertString extends UDF {
    
    
    public Text evaluate(Text line) {
    
    
        if (null != line && !line.toString().equals("")) {
    
    
            String str = line.toString();
            char[] rs = new char[str.length()];
            for (int i = str.length() - 1; i >= 0; i--) {
    
    
                rs[str.length() - 1 - i] = str.charAt(i);
            }
            line.set(new String(rs));
            return line;
        }
        line.set("");
        return line;
    }
}

打成包含依赖的jar包:

上传到linux虚拟机中

添加到hive中：

add jar /apps/testHive-v2.jar;

设置函数名，关联类名

create temporary function my_revert_v2 as 'com.alan.RevertString';

测试：

select my_revert_v2('abc');