[PIG-2151] Add annotation to specify output schema in Java UDFs - ASF JIRA

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Release Note:

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An EvalFunc can annotated with an @OutputSchema annotation to
tell Pig what the expected output is. This can be used in place
of EvalFunc.outputSchema(Schema inpSchema)

The default implementation of EvalFunc.outputSchema(Schema inpSchema) will look at this annotation and return an interpreted schema, if the annotation is present.

Implementing a custom EvalFunc.outputSchema(Schema inpSchema) will override the annotation (unless you deal with it explicitly, or by calling super.outputSchema(schema))

Here's an example of a complex schema declared in an annotation:
@OutputSchema("y:bag{t:tuple(len:int,word:chararray)}")

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An EvalFunc can annotated with an @OutputSchema annotation to tell Pig what the expected output is. This can be used in place of EvalFunc.outputSchema(Schema inpSchema) The default implementation of EvalFunc.outputSchema(Schema inpSchema) will look at this annotation and return an interpreted schema, if the annotation is present. Implementing a custom EvalFunc.outputSchema(Schema inpSchema) will override the annotation (unless you deal with it explicitly, or by calling super.outputSchema(schema)) Here's an example of a complex schema declared in an annotation: @OutputSchema("y:bag{t:tuple(len:int,word:chararray)}")

In Python udfs, the output schema of an eval func is specified via an @OutputSchema annotation.

We should do the same for Java udfs instead of making people write the cumbersome outputSchema functions.