UDF函数 

UDF函数可以直接应用于select语句，对查询结构做格式化处理输出内容。自定义UDF需要继承org.apache.hadoop.hive.ql.UDF,实现evaluate函数。
自定义udf函数步骤：
  1.继承UDF类
  2.重写evaluate方法
  3.把项目打成jar包
  4.hive中执行命令add jar /home/jrjt/dwetl/PUB/UDF/udf/GetProperty.jar;
  5.创建函数create temporary function get_pro as 'jd.Get_Property'//jd.jd.Get_Property为类路径;
永久udf函数创建：
  1、hdfs dfs -put udftimestamp.jar /udf/
  2、add jar hdfs://nameservice1:8020/udf/udftimestamp.jar;
  3、CREATE FUNCTION dm_lots.udftimestamp AS 'mytimestamp.MyUDFTimestamp' using jar 'hdfs://nameservice1:8020/udf/udftimestamp.jar';
删除udf函数
drop function dm_lots.udftimestamp;
查看udf函数
show functions
例1：日志切割

import org.apache.hadoop.hive.ql.exec.UDF;import org.apache.hadoop.io.Text;public class SalaryUDF extends UDF{public Text evaluate(Text salaryText){//1.if salary is nullif (salaryText == null) {return null;}String salaryStr = salaryText.toString();//2.if salary is not double typedouble salary = 0.0;try {salary = Double.valueOf(salaryStr);} catch (NumberFormatException e) {e.printStackTrace();return null;}Text text = new Text();//3.panduan salary return string if (salary > 10000) {text.set("you are rich");return text;}else if (salary <= 10000 && salary > 5000) {text.set("income is normal");return text;}else {text.set("income is pool");return text;}}}

例2：日期转化

package com.rainbow.udf;import java.text.SimpleDateFormat;import java.util.Date;import org.apache.hadoop.hive.ql.exec.UDF;import org.apache.hadoop.io.Text;public class TestDate extends UDF{  private SimpleDateFormat inputdateFormat = new SimpleDateFormat("dd/MM/yyyy:HH:mm:ss",locale.ENLISH);  private SimpleDateFormat outputdateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");   public Text exvaluate(Text input){     Text output = new Text();   if(null==input){     return null;}   if(null==input.toString()){     return null;}   try {      String inputDate=input.toString().trim();      Date perseDate = inputdateFormat.parse(inputDate);      String outputDate = outputdateFormat.format(perseDate);      output.set(outputDate);}catch(Exception e){    e.printStackTrace();    return output;}       return output;}}

打jar包 
上传到hdfs
CREATE FUNCTION [db_name.]function_name AS class_name [USING JAR|FILE|ARCHIVE'file_uri' [, JAR|FILE|ARCHIVE'file_uri'] ];