Hadoop-Hive 自定义函数实现步骤

1. 创建maven java 工程，导入jar包

    <repositories>
        <repository>
            <id>cloudera</id>
     <url>https://repository.cloudera.com/artifactory/cloudera-repos/</url>
        </repository>
    </repositories>
    <dependencies>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.6.0-cdh5.14.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hive</groupId>
            <artifactId>hive-exec</artifactId>
            <version>1.1.0-cdh5.14.0</version>
        </dependency>
    </dependencies>
    <build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.0</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <encoding>UTF-8</encoding>
            </configuration>
        </plugin>
         <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-shade-plugin</artifactId>
             <version>2.2</version>
             <executions>
                 <execution>
                     <phase>package</phase>
                     <goals>
                         <goal>shade</goal>
                     </goals>
                     <configuration>
                         <filters>
                             <filter>
                                 <artifact>*:*</artifact>
                                 <excludes>
                                     <exclude>META-INF/*.SF</exclude>
                                     <exclude>META-INF/*.DSA</exclude>
                                     <exclude>META-INF/*/RSA</exclude>
                                 </excludes>
                             </filter>
                         </filters>
                     </configuration>
                 </execution>
             </executions>
         </plugin>
    </plugins>
    </build>
   

2. 开发java类继承UDF，并重载evaluate 方法

    public class 类名 extends UDF {
    	    public 返回值 evaluate(参数) {
    	       
        }
    }
   

3. 将我们的项目打包，并上传到hive的lib目录下

4. 设置函数与我们的自定义函数关联

    创建临时函数
    create temporary function 函数名 as '类名';
     
    删除临时函数
    drop temporary function 函数名;
    
    
    创建永久函数
    create function  函数名 as '类名';
    删除永久函数
    drop   function 函数名;
   

5. 使用自定义函数

    select 函数名(字段);