Do I have to create new instance for each instance of Validator?

[Stefan Jankovic]

When validating objects using Validator interface (with supports() and validate() methods) I first make a class that implements Validator and then logically implement those two methods. After that I invoke it inside some controller. Question is related concurrency and thread safety and it is: do I make new instance of Validator each time I am validating something, or I can make Validator instance singleton and simple inject it in my controller? Can something go wrong if I use same instance of Validator for each REST request in controller?

[Rob Spoor]

Stefan Jankovic wrote:Can something go wrong if I use same instance of Validator for each REST request in controller?

If the Validator instance is thread-safe or, even better, immutable, then feel free to create a singleton and inject it. If it isn't, make it request scoped and still inject it. Let Spring worry about instantiating it.

[Tim Holloway]

I cannot speak with full authority on Spring validators specifically, but as a general rule, validators are stateless. Their primary purpose is to accept an input and return judgement with no long-term context. So no. Besides, if the validator is a Spring Bean, Spring Beans are by default singletons anyway.