Can also use checkerframework to statically analyze your code for NPEs. It effectively augments the type system to require you to handle nulls where appropriat

Can also use checkerframework to statically analyze your code for NPEs. It effectively augments the type system to require you to handle nulls where appropriate. It doesn't recognize I/O boundaries for you, you have to make sure those are annotated properly, but after that with sensible defaults, you can be more confident of the NPE-free-ness of your code.