I have one usecase where i need to do some computation on rows which are usecase specific. i want to write custom transformations in java and register it as UDF in BigQuery. so that with BigQuery SQL i can use it like function.
How i can do it? anybody knows the process to register java code with BigQuery?
Unfortunately not possible. You can use only JavaScript as you can see here.
As mentioned by @guillaumeblaquiere, you could try using remote functions with cloud functions in Java