Hive面试题(5)UDF,UDTF（二）UDTF

1.udtf介绍及编写

1.1.介绍

HIVE中udtf可以将一行转成一行多列，也可以将一行转成多行多列，使用频率较高。本篇文章通过实际案例剖析udtf的编写及使用方法和原理。阅读本篇文章前请先阅读UDF编写

测试数据

drop table if exists test;
  create table test
  (
    ind int,
    col string,
    col1 string
  ) ;
  insert into test values (1,'a,b,c','1,2');
  insert into test values (2,'j,k',null);
  insert into test values (3,null,null) ;

对第一行需要输出如下结果：

Ind	Key	Value
1	a	1
1	b	2
1	c	Null

其它行都要输出类似数据，如果输入数据为null，则没输出。

1.2udtf编写

编写UDTF(User-Defined Table-Generating Functions)，需要继承GenericUDTF类，类中部分代码如下：

/**
   * A Generic User-defined Table Generating Function (UDTF)
   *
   * Generates a variable number of output rows for a single input row. Useful for
   * explode(array)...
   */
  public abstract class GenericUDTF {
  ​
    public StructObjectInspector initialize(StructObjectInspector argOIs)
          throws UDFArgumentException {
        List<? extends StructField> inputFields = argOIs.getAllStructFieldRefs();
        ObjectInspector[] udtfInputOIs = new ObjectInspector[inputFields.size()];
        for (int i = 0; i < inputFields.size(); i++) {
          udtfInputOIs[i] = inputFields.get(i).getFieldObjectInspector();
        }
        return initialize(udtfInputOIs);
    }
    
    /**
       * Give a set of arguments for the UDTF to process.
       *
       * @param args
       *          object array of arguments
       */
    public abstract void process(Object[] args) throws HiveException;
  ​
    /**
       * Called to notify the UDTF that there are no more rows to process.
       * Clean up code or additional forward() calls can be made here.
       */
    public abstract void close() throws HiveException;
  }

继承GenericUDTF需要实现以上方法，其中initialize方法和UDF中类似，主要是判断输入类型并确定返回的字段类型。process方法对udft函数输入的每一样进行操作，通过调用forward方法返回一行或多行数据。close方法在process调用结束后调用，用于进行其它一些额外操作，只执行一次。

package com.practice.hive.udtf;
  ​
  import java.util.List;
  ​
  import com.google.common.collect.Lists;
  import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
  import org.apache.hadoop.hive.ql.metadata.HiveException;
  import org.apache.hadoop.hive.ql.udf.generic.GenericUDTF;
  import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
  import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
  import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;
  import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
  ​
  /**
   * @author liufeifei
   * @date 2018/06/20
   */
  public class ArrToMapUDTF extends GenericUDTF {
  ​
      private String[] obj = new String[2];
  ​
      /**
       * 返回类型为 String，string
       *
       * @param argOIs
       * @return
       * @throws UDFArgumentException
       */
      @Override
      public StructObjectInspector initialize(StructObjectInspector argOIs) throws UDFArgumentException {
          List<String> colName = Lists.newLinkedList();
          colName.add("key");
          colName.add("value");
          List<ObjectInspector> resType = Lists.newLinkedList();
          resType.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);
          resType.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);
          // 返回分别为列名 和 列类型
          return ObjectInspectorFactory.getStandardStructObjectInspector(colName, resType);
      }
  ​
      @Override
      public void process(Object[] args) throws HiveException {
          if(args[0] == null) {
              return;
          }
          String arg1 = args[0].toString();
  ​
          String[] arr1 = arg1.split(",");
          String[] arr2 = null;
          if(args[1] != null) {
              arr2 = args[1].toString().split(",");
          }
  ​
          for(int i = 0; i < arr1.length ; i++ ) {
              obj[0] = arr1[i];
              if(arr2 != null && arr2.length > i) {
                  obj[1] = arr2[i];
              } else {
                  obj[1] = null;
              }
              forward(obj);
          }
      }
  ​
      @Override
      public void close() throws HiveException {
      }
  }