DB transaction or Java DAO's method synchronization?

Question

I have Java-based web server, and I also have DAO singleton object with method, whose SQL operations\' logic must be synchronized in some way in order to guarantee data integri

Answer 1

Depends deeply in what is what you want to synchronize, synchronization is about resources, if you have more than one database in your code, and the data integrity problem is distributed, you need a transaction context, not only declaring it but knowing how to manage it properly. Assuming you have a single database and assuming your problem is integrity caused by a possible inconsistency of a SELECT clause with a UPDATE or INSERT clause happening later in the method, The right solution would be a DB transaction and the use of a SELECT FOR UPDATE clause. If your problem is about UPDATE/INSERT of different tables in the same operation you may have two resources, one is including CONSTRAINTS, this is the preferred method, but in some cases is not possible. In the case that a CONTRAINT is not possible, consider a redesign of your DATAMODEL as managing this kind of problems synchronyzing app code is the worst solution, but even so is a solution.