hive UDF 1.2.2

package com.cc.hiveudf;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDFUtils;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;

@Description(name="nvl",value="_FUNC_(value,defaultValue) -Returns default value if value is null else return value",extended="select _FUNC_(null,val) frm src limit 1;")
public class UdfT1 extends GenericUDF{
	
	private GenericUDFUtils.ReturnObjectInspectorResolver returnObjectInspactorResolver; //通过获取非null值的变量的类型，并通过这个数值，确定返回值的类型
	private ObjectInspector[] argumentOIs;
	
	@Override
	public Object evaluate(DeferredObject[] arg0) throws HiveException {
		//returnObjectInspactorResolver 用户从 DeferredObject 对象数组中获取值，并返回
		Object returnVal = returnObjectInspactorResolver.convertIfNecessary(arg0[0], argumentOIs[0]);
		if(returnVal == null)
		{
			returnVal = returnObjectInspactorResolver.convertIfNecessary(arg0[1], argumentOIs[1]);
		}
		return returnVal;
	}

	//在hadoop task 内部显示调试信息
	@Override
	public String getDisplayString(String[] arg0) {
		StringBuilder sb = new StringBuilder();
		sb.append("if");
		sb.append(arg0[0]);
		sb.append("is null returns"+arg0[1]);
		return sb.toString();
	}
	
	/*
	 * (non-Javadoc)
	 * @see org.apache.hadoop.hive.ql.udf.generic.GenericUDF#initialize(org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector[])
	 * 会被输入的每个参数调用，目标是确定参数的返回类型
	 */
	@Override
	public ObjectInspector initialize(ObjectInspector[] arg0) throws UDFArgumentException {
		
		argumentOIs = arg0;
		if(arg0.length != 2)
		{
			throw new UDFArgumentLengthException("The operate 'nvl' accept 2 arguments!");
		}
		
		returnObjectInspactorResolver = new GenericUDFUtils.ReturnObjectInspectorResolver(true);
		if(!(returnObjectInspactorResolver.update(argumentOIs[0]) && returnObjectInspactorResolver.update(argumentOIs[1])))
		{
			throw new UDFArgumentTypeException(2, "1st and 2nd args of func NVL shoud have same type but 1st type"+argumentOIs[0].getTypeName()+" 2nd type:"+argumentOIs[1].getTypeName());
		}
		return returnObjectInspactorResolver.get();
	}
	
}

添加jar包到classpath

hive> add jar /home/hadoop/funNvl.jar;

hive> create temporary function nvl as 'org.apache.hadoop.hive.ql.udf.generic.UdfT1';

hive> select nvl(null,1) from china limit 1;
OK
1
Time taken: 1.578 seconds, Fetched: 1 row(s)

hive> select nvl(1,"nihao") from china limit 1;
OK
1
Time taken: 0.112 seconds, Fetched: 1 row(s)

包名似乎需要固定写成这个：org.apache.hadoop.hive.ql.udf.generic