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Hive, mail # user - Using Reflect: A thread for ideas


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Using Reflect: A thread for ideas
John Omernik 2013-02-14, 04:38
I stumbled across the little documented reflect function today. I've always
known about it, but java scares me if it's not in a cup so I didn't dig.
 Well today I dug, and found an awesome use case for reflect (for me) and
wanted to share.  I also thought it would be nice to validate some thoughts
I had on reflect, and how we could possibly share ideas on reflect so that
folks could get more use out of this great feature of hive.

Here's my example: A simple URL decode function:

select url, reflect('java.net.URLDecoder', 'decode', url, 'utf-8') as
decoded_url from logs
Basically I am using the decode function of the java.net.URLDecoder class.
 Pretty awesome, works great, no files to distribute either.  Even works
through JDBC!

Ok that being said, I realized now that the function I am trying to call
has to return data in a simple data type.  For example, I struggle to come
up with a simple reflect() for making an Hex MD5 out of a string because
the built in function return an object, which have methods that can return
what I am looking for. Which is great, but then I have to compile java
code, distribute a jar, and then run the code. I am looking for simple like
the URLDecoding function.

I love this reflect feature, but I think it's probably underutilized due to
the perceived usability issues for beginners.  So that leads me to my next
thought. What if we brain storm here handy functions in Java that are not
included in the standard hive language, that make the transition to hive
well using the reflect function and the show an example of it's use? I went
first with my URLDecode, and obviously will be looking for more, but have
you seen some examples that we neat and worked well for you? Can you share?
Perhaps if we get enough examples we could roll some of these into a wiki
page on the hive wiki that folks can use to get over the "perceived"
complexity of using java reflect?

Thanks to those who have worked hard to implement features like this, it is
truly awesome.