hive UDF 编程

<dependency>
            <groupId>org.apache.hive</groupId>
            <artifactId>hive-exec</artifactId>
            <version>2.3.0</version>
</dependency>

public abstract class GenericUDF implements Closeable {
     ...
     /* 实例化后initialize方法只会调用一次
        - 参数arguments即udf接收的参数列表对应的objectinspector
        - 返回的ObjectInspector对象就是udf返回值的对应的objectinspector
      initialize方法中往往做的工作是检查一下arguments是否和你udf需要的参数个数以及类型是否匹配。
     */
     
     public abstract ObjectInspector initialize(ObjectInspector[] arguments)
      throws UDFArgumentException;
     ...
      // 真正的udf逻辑在这里实现
      // - 参数arguments即udf函数输入数据，这个数组的长度和initialize的参数长度一样
      // 
      public abstract Object evaluate(DeferredObject[] arguments)
      throws HiveException;
}

public class DateFeaker extends GenericUDF{
    private static final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    
      private transient ObjectInspectorConverters.Converter[] converters;

      @Override
      public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
        if (arguments.length != 2) {
          throw new UDFArgumentLengthException(
              "The function date_util(startdate,enddate) takes exactly 2 arguments.");
        }

        converters = new ObjectInspectorConverters.Converter[arguments.length];
        for (int i = 0; i < arguments.length; i++) {
          converters[i] = ObjectInspectorConverters.getConverter(arguments[i],
              PrimitiveObjectInspectorFactory.writableStringObjectInspector);
        }

        return ObjectInspectorFactory
            .getStandardListObjectInspector(PrimitiveObjectInspectorFactory
                .writableStringObjectInspector);
      }
      


    @Override
    public Object evaluate(DeferredObject[] arguments) throws HiveException {
        if (arguments.length != 2) {
              throw new UDFArgumentLengthException(
                  "The function date_util(startdate,enddate) takes exactly 2 arguments.");
            }
        
        ArrayList<Text> temp = new ArrayList<Text>();
        
        if (arguments[0].get() == null || arguments[1].get() == null) {
            return null;
         }
        System.out.println(converters[0].getClass().getName());
        System.out.println(arguments[0].getClass().getName());
        Text startDate = (Text) converters[0].convert(arguments[0].get());
        Text endDate = (Text) converters[1].convert(arguments[1].get());
        Date start;
        try {
            start = sdf.parse(startDate.toString());
        } catch (ParseException e) {
            e.printStackTrace();
            throw new UDFArgumentException(
                    "The First Argument does not match the parttern yyyy-MM-dd "+arguments[0].get());
        }
        Date end;
        try {
            end = sdf.parse(endDate.toString());
        } catch (ParseException e) {
            e.printStackTrace();
            throw new UDFArgumentException(
                    "The Second Argument does not match the parttern yyyy-MM-dd "+arguments[1].get());
        }
        Calendar  c = Calendar.getInstance();
        while(start.getTime()<=end.getTime()){
            temp.add(new Text(sdf.format(start)));
            c.setTime(start);
            c.add(Calendar.DATE, 1);
            start = c.getTime();
        }
        return temp;
    }

    @Override
    public String getDisplayString(String[] children) {
        assert (children.length == 2);
        return getStandardDisplayString("date_util", children);
    }

[hadoop@hadoop001 lib]$hadoop fs -put  g6-hadoop-1.0.jar hdfs://chd:8020/user

hive> add jar /home/hadoop/data/hive/g6-hadoop-1.0.jar;

CREATE TEMPORARY FUNCTION function_name AS class_name;   

function_name函数名                        

*******class_name 类路径，包名+类名*********   这里就是你写的UDF函数的第一行的package后边的东西然后在加个点加个类的名字

CREATE TEMPORARY FUNCTION function_name AS class_name USING JAR path;

function_name函数名                        

class_name 类路径，

包名+类名 

path jar包hdfs路径

CREATE FUNCTION HelloUDF AS ‘org.apache.hadoop.hive.ql.udf.HelloUDF‘

USING JAR ‘hdfs://hadoop001:9000/lib/g6-hadoop-1.0.jar‘;

#测试 hive> select HelloUDF("17") ;

OK hello:17