Bean with singleton scope and with states

I know there are already tons of questions on this. But they don't clarify my doubts.

It is recommended here that to achieve thread safety, design your beans stateless. I don't understand it.

If I have a service class and it has only one state in it (and no other instance variables).

@Service
class MyService

@Autowired
MyRepository repository;

//business method that call repository methods




MyRepository has a default singleton scope. It has org.springframework.data.mongodb.core.MongoTemplate autowired. And that's the only instance variable I have in MyReporitory.

MyRepository

org.springframework.data.mongodb.core.MongoTemplate

MyReporitory

@Repository
class MyRepository
@Autowired
MongoTemplate mongo;
//methods that use MongoTemplate reference



So what is the deal here? Is service/repository thread safe?

1 Answer
1

If your repository reference is immutable (only autowired once, or set during service object construction) then your service bean is thread-safe.

Generally speaking, when multiple threads access the state of a bean simultaneously and that state is mutable (can change) you have potential threading issues. If the state is immutable and it's being read by multiple threads you need not worry about multi-threading issues.

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