HIVE中UDTF使用说明

1. UDTF介绍

UDTF(User-Defined Table-Generating Functions)  用来解决 输入一行输出多行(On-to-many maping) 的需求。

2. 编写自己需要的UDTF

• 继承org.apache.hadoop.hive.ql.udf.generic.GenericUDTF。
• 实现initialize, process, close三个方法
• UDTF首先会调用initialize方法，此方法返回UDTF的返回行的信息（返回个数，类型）。初始化完成后，会调用process方法，对传入的参数进行处理，可以通过forword()方法把结果返回。最后close()方法调用，对需要清理的方法进行清理。

下面是我写的一个用来切分”key:value;key:value;”这种字符串，返回结果为key, value两个字段。供参考：

 1: import java.util.ArrayList;

 2:

 3: import org.apache.hadoop.hive.ql.udf.generic.GenericUDTF;

 4: import org.apache.hadoop.hive.ql.exec.UDFArgumentException;

 5: import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;

 6: import org.apache.hadoop.hive.ql.metadata.HiveException;

 7: import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;

 8: import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;

 9: import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;

 10: import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;

 11:

 12: public class ExplodeMap extends GenericUDTF{

 13:

 14: @Override

 15: public void close() throws HiveException {

 16: // TODO Auto-generated method stub 

 17: }

 18:

 19: @Override

 20: public StructObjectInspector initialize(ObjectInspector[] args)

 21: throws UDFArgumentException {

 22: if (args.length != 1) {

 23: throw new UDFArgumentLengthException("ExplodeMap takes only one argument");

 24: }

 25: if (args[0].getCategory() != ObjectInspector.Category.PRIMITIVE) {

 26: throw new UDFArgumentException("ExplodeMap takes string as a parameter");

 27: }

 28:

 29: ArrayList fieldNames = new ArrayList();

 30: ArrayList fieldOIs = new ArrayList();

 31: fieldNames.add("col1");

 32: fieldOIs.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);

 33: fieldNames.add("col2");

 34: fieldOIs.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);

 35:

 36: return ObjectInspectorFactory.getStandardStructObjectInspector(fieldNames,fieldOIs);

 37: }

 38:

 39: @Override

 40: public void process(Object[] args) throws HiveException {

 41: String input = args[0].toString();

 42: String[] test = input.split(";");

 43: for(int i=0; i
			

				

			
 44: try {
			

				

			
 45: String[] result = test[i].split(":");
			

				

			
 46: forward(result);
			

				

			
 47: } catch (Exception e) {
			

				

			
 48: continue;
			

				

			
 49: }
			

				

			
 50: }
			

				

			
 51: }
			

				

			
 52: }
			

				

			
		

3. 使用方法

UDTF有两种使用方法，一种直接放到select后面，一种和lateral view一起使用。

1：直接select中使用：select explode_map(properties) as (col1,col2) from src;

• 不可以添加其他字段使用：select a, explode_map(properties) as (col1,col2) from src
• 不可以嵌套调用：select explode_map(explode_map(properties)) from src
• 不可以和group by/cluster by/distribute by/sort by一起使用：select explode_map(properties) as (col1,col2) from src group by col1, col2

2：和lateral view一起使用：select src.id, mytable.col1, mytable.col2 from src lateral view explode_map(properties) mytable as col1, col2;

• 此方法更为方便日常使用。执行过程相当于单独执行了两次抽取，然后union到一个表里。