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Reflect (Generic) UDF

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.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.

Note that Reflect UDF is non-deterministic since there is no guarantee what a specific method will return given the same parameters. So be cautious when using Reflect on the WHERE clause because that may invalidate Predicate Pushdown optimization.

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