How to create temporary procedures in MySQL?

I don't think you can. My recommendation would be to create the "stored procedure" in Java. Write a method that takes your inputs, performs queries and calculations, then returns the dataset.

I guess you are looking for anonymous code blocks / anonymous procedures. Unfortunately it isn't supported in MySQL (it is supported in "big" RDBMSs such as Oracle or Sybase)

I would consider using some ORM framework, but I am not a Java developer, so I can't recommend any of them.