hive自定义函数，

hive自定义函数，

1.创建类，继承UDF
  package com.hivedemo.udf;   import org.apache.hadoop.hive.ql.exec.Description;
  import org.apache.hadoop.hive.ql.exec.UDF;   /**
   * 自定义hive函数
   */
  @Description(name = "myadd",
    value = "myadd(int a , int b) ==> return a + b ",
    extended = "Example:\n"
      + " myadd(1,1) ==> 2 \n"
      + " myadd(1,2,3) ==> 6;")
  public class AddUDF extends UDF {    public int evaluate(int a ,int b) {
    return a + b ;
   }    public int evaluate(int a ,int b , int c) {
    return a + b + c;
   }
  }
 2.打成jar包。
  cmd>cd {classes所在目录}
  cmd>jar cvf HiveDemo.jar -C x/x/x/x/classes/ .
 3.添加jar包到hive的类路径
  //添加jar到类路径
  $>cp /mnt/hgfs/downloads/bigdata/data/HiveDemo.jar /soft/hive/lib
 
 3.重进入hive
  $>....  4.创建临时函数
  //
  CREATE TEMPORARY FUNCTION myadd AS 'com.it18zhang.hivedemo.udf.AddUDF';  5.在查询中使用自定义函数
  $hive>select myadd(1,2)  ;
 
 6.定义日期函数
  1)定义类
  public class ToCharUDF extends UDF {
   /**
    * 取出服务器的当前系统时间 2017/3/21 16:53:55
    */
   public String evaluate() {
    Date date = new Date();
    SimpleDateFormat sdf = new SimpleDateFormat();
    sdf.applyPattern("yyyy/MM/dd hh:mm:ss");
    return sdf.format(date) ;
   }
   public String evaluate(Date date) {
    SimpleDateFormat sdf = new SimpleDateFormat();
    sdf.applyPattern("yyyy/MM/dd hh:mm:ss");
    return sdf.format(date) ;
   }    public String evaluate(Date date,String frt) {
    SimpleDateFormat sdf = new SimpleDateFormat();
    sdf.applyPattern(frt);
    return sdf.format(date) ;
   }
  }   2)导出jar包，通过命令添加到hive的类路径(不需要重进hive)。
   $hive>add jar /mnt/hgfs/downloads/bigdata/data/HiveDemo-1.0-SNAPSHOT.jar
  
  3)注册函数
   $hive>CREATE TEMPORARY FUNCTION to_char AS 'com.it18zhang.hivedemo.udf.ToCharUDF';
   $hive>CREATE TEMPORARY FUNCTION to_date AS 'com.it18zhang.hivedemo.udf.ToDateUDF';