How spring single tone bean works

We have a back end application with Spring IOC with jersey rest. All the spring bean we defended is as default , I mean single tone.

This application is DB eccentric application and number of user is also huge. Now my question is that how spring single note bean manage the concurrency over this application. None of the method in service classes are defined as synchronized but we never get any issue with user data synchronization. Ever thing looks perfectly ok.

I think I am missing something to understand the spring single tone bean or how spring handle multiple request with single tone object.

As per my understanding as spring bean are single tone and no service method is defined as synchronized there must be some synchronization issue with multiple request.

Any one can help me to understand the thing properly....