Hive调用Java类ReflectUDF

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关于Hive调用Java类的方法，Hive的官方描述如下：

ReflectUDF

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• Created by Lefty Leverenz, last modified on Jul 21, 2014

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Reflect (Generic) UDF：必须是静态方法

A Java class and method often exists to handle the exact function a user would like to use in Hive. Rather than having to write a wrapper UDF to call this method, the majority of these methods can be called using reflect UDF. Reflect uses Java reflection to instantiate and call methods of objects; it can also call static functions. The method must return a primitive type or a type that Hive knows how to serialize.

SELECT reflect( "java.lang.String" ,  "valueOf" ,  1 ),        reflect("java.util.UUID", "randomUUID"),         reflect( "java.lang.String" ,  "isEmpty" ),         reflect( "java.lang.Math" ,  "max" ,  2 ,  3 ),         reflect( "java.lang.Math" ,  "min" ,  2 ,  3 ),         reflect( "java.lang.Math" ,  "round" ,  2.5 ),         reflect( "java.lang.Math" ,  "exp" ,  1.0 ),         reflect( "java.lang.Math" ,  "floor" ,  1.9 ) FROM src LIMIT  1 ;     1    true     3    2    3    2.7182818284590455   1.0

Version information

As of Hive 0.9.0, java_method() is a synonym for reflect(). See Misc. Functions in Hive Operators and UDFs.

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1. Lefty Leverenz

   This doc comes from the Hive xdocs, with minor edits. It is included here because the xdocs are currently unavailable (Feb. 2013).