Spring - injection java.util classes

Question

I'm working on java.util classes injection, with Spring.

I wonder, do you register your bean classes like Scanner or Random in Spring's context?

I guess this decision depends on how often you will use it, right?

What is the number of usages when I should consider returning bean instead of creating a new object?

Answer 1

Do you want multiple beans to share a single source of random numbers? If so, then the beans needs to be injected with a random number generator bean.

It is however recommended to use ThreadLocalRandom in a multi-threaded program (for better performance), and it doesn't hurt in a single-threaded program, so general recommendation is to use that, which means Random should never be a Spring bean.

However, if you need to unit test code, using a seeded random number sequence, then code needs to be injected with a random number bean that can be mocked.

Note however, that such random number bean is not the Random class itself, but a wrapper/helper bean.

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Do you want multiple beans to share a single Scanner ?

That question really only makes sense in a command-line program, reading System.in , in which case answer is yes.