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https://issues.apache.org/jira/browse/PIG-1678?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Olga Natkovich updated PIG-1678:
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Fix Version/s: (was: 0.9.0)
> Need a easy way to bind to external Java library functions that require
> object constructors such as Apache Commons Math library
> -------------------------------------------------------------------------------------------------------------------------------
>
> Key: PIG-1678
> URL: https://issues.apache.org/jira/browse/PIG-1678
> Project: Pig
> Issue Type: New Feature
> Reporter: David Ciemiewicz
>
> I would like to have a trivial way to bind and invoke Java library functions
> from within Pig without creating wrapper functions in Java. In particular,
> there is need to do this for dynamic (non-static) class methods which first
> require creation of a class instance object to invoke the method.
> Note that the new Pig 0.8 built-in function Invoker only works for static
> class methods and does not support instantiation of class objects and
> subsequent dynamic method invocation.
> For instance, I need functions out of the Apache Commons Math library
> (http://commons.apache.org/math/) such as
> BetaDistributionImpl.cumulativeProbability.
>
> http://commons.apache.org/math/apidocs/org/apache/commons/math/distribution/BetaDistributionImpl.html
> To use this class, I must first create a new object with a parameterized
> constructor -- BetaDistributionImpl(alpha,beta) and then I can invoke a
> method. This two stage process of object instantiation and then method
> invocation is a bit clumsy, necessitating a wrapper function.
> I would like to be able to do a simple Pig definition to declare a binding to
> and instantiate instances of a Java class and invoke methods on these
> instances. In the case of Apache Commons Math distribution
> BetaDistributionImpl, I must parameterize the objection creation with values
> from my data I am processing with Pig followed by an invocation of a method
> with a third parameter.
> {code}
> register commons-math-2.1.jar;
> define (new
> org.apache.commons.math.distribution.BetaDistributionImpl((double) alpha,
> (double) beta))
> . cumulativeProbability((double) x) BetaIncomplete(x, alpha, beta)
> {code}
> Writing a Pig Eval<Double> wrapper function that does the same thing requires
> about 100 lines of Java code to implement the binding to do all the necessary
> comments, imports, parameter coercions, exception handling and output scheme
> declarations. And that's just one wrapper for one method. The class has on
> the order of 10-20 methods and there are on the order of 100-200 classes.
> And alternate form to consider is if I could just say something like:
> {code}
> register commons-math-2.1.jar;
> import org.apache.commons.math.distribution.BetaDistributionImpl as BetaDist;
> B = foreach A as
> alpha,
> beta,
> x,
> BetaDist(alpha,beta).cumulativeProbability(x) as prob;
> {code}
> Ideally I'd be able to register or include a list of all the bindings to the
> library.
> Of course in the case, Pig should automatically coerce all parameters to
> their corresponding implementation types e.g. a double parameter in the Java
> function would dictate that Pig coerce int, long, float, double, chararray,
> and bytearray to double automagically (albeit some compiler warning might be
> warranted).
> One question about this proposal is how to handle methods that throw
> exceptions such as:
> {code}
> public double cumulativeProbability(double x) throws MathException
> {code}
> I think I would propose that Pig provide a means for handling the exception
> case such as a simple annotation in the declaration:
> {code}
> register commons-math-2.1.jar;
> import org.apache.commons.math.distribution.BetaDistributionImpl as BetaDist,
> return null on (MathException, Exception);
> {code}
> Or we could get even more fancy and permit wholesale default handling for
> every method that might throw an exception:
> {code}
> register commons-math-2.1.jar as ApacheMathCommons;
> ApacheMathCommons warn and return null on (MathException, AnyException);
> import org.apache.commons.math.distribution.BetaDistributionImpl as BetaDist;
> {code}
> I'm sure if people think about it, there are probably potentially cleaner
> ways to import the bindings and handle exceptions cases.
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