Hive调用Java类ReflectUDF

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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   Lefty Leverenz

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