前言

老版本编写UDF时，需要继承 org.apache.hadoop.hive.ql.exec.UDF类，然后直接实现evaluate()方法即可。
由于公司hive版本比较高（3.x）,这次编写UDF就采用了新的版本，继承类org.apache.hadoop.hive.ql.udf.generic.GenericUDF，实现三个方法

1. 新建项目

打开IDEA，新建一个项目，基本配置如下，Archetype选择图中所示

2.配置maven依赖

导入编写UDF需要用到的依赖

<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>
      <exclusions>
        <exclusion>
          <groupId>org.apache.commons</groupId>
          <artifactId>commons-compress</artifactId>
        </exclusion>
      </exclusions>
    </dependency>
<build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>8</source>
          <target>8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>

3.编写代码

目录结构可自行定义，这块不影响实际功能，代码整体框架如下
我这里代码传入三列数据，返回一列数据，入参可以判断一下是否传入数据正确，以及数据类型是否匹配
主要实现三个方法，具体内容在代码块中有说明

1. initialize
2. evaluate
3. getDisplayString

public class ComputeUnitPrice extends GenericUDF {
 WritableHiveDecimalObjectInspector  decimalObjectInspector;

    //初始化方法，做一些检查
    @Override
    public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
        // 判断输入参数的个数
        if(arguments.length !=3){
            throw new UDFArgumentLengthException("This UDF Only takes 3 arguments: String, String, Decimal");
        }
        ObjectInspector param1 = arguments[0];
        ObjectInspector param2 = arguments[1];
        ObjectInspector param3 = arguments[2];
        // 判断输入参数的类型
        if(!(param1 instanceof StringObjectInspector)){
            throw new UDFArgumentException("Param1 Type is error,Must be : String");
        }
        if(!(param2 instanceof StringObjectInspector)){
            throw new UDFArgumentException("Param2 Type is error,Must be : String");
        }
//        if(!(param3 instanceof JavaConstantHiveDecimalObjectInspector)){
//            throw new UDFArgumentException("Param3 Type is error,Must be : JavaHiveDecimal");
//        }
        this.decimalObjectInspector = (WritableHiveDecimalObjectInspector ) param3;
        //函数返回值为 Decimal，需要返回 Decimal类型的鉴别器对象
        return PrimitiveObjectInspectorFactory.javaHiveDecimalObjectInspector;
    }
}

    @Override
    public Object evaluate(DeferredObject[] arguments) throws HiveException {
        //计算逻辑编写
    }

	//udf的说明
	@Override
    public String getDisplayString(String[] children) {
        return "ComputeUnitPrice";
    }


    //main方法测试一下数据结果
	public static void main(String[] args) throws HiveException {
        ComputeUnitPrice computeUnitPrice = new ComputeUnitPrice();

        DeferredObject[] param = {new DeferredJavaObject("箱"), new DeferredJavaObject("800g*8袋/箱"), new DeferredJavaObject(100.20)};
        JavaDoubleObjectInspector javaDoubleObjectInspector = PrimitiveObjectInspectorFactory.javaDoubleObjectInspector;

        ObjectInspector stringOi = PrimitiveObjectInspectorFactory.javaStringObjectInspector;
        ObjectInspector doubleOi = PrimitiveObjectInspectorFactory.javaDoubleObjectInspector;
        computeUnitPrice.initialize(new ObjectInspector[]{stringOi, stringOi,doubleOi});
        double res =  javaDoubleObjectInspector.get(computeUnitPrice.evaluate(param));
        System.out.println("res " + res);
       
    }

4.打jar包

将项目打成jar包

mvn clean package

执行完成，target目录下寻找自己的jar包

5.上传服务器

本地上传到机器，再由机器上传到hdfs或者s3等

6.代码中引用

add jars xxxxx/compute_sku_unit_price.jar;
create temporary function compute_sku_unit_price as 'xx.xxx.xxx.xxx.ComputeUnitPrice';
${your_sql};