Where should "@Transactional" be placed Service Layer or DAO

Ideally, Service layer (Manager) represents your business logic and hence it should be annotated with @Transactional.

Service layer may call different DAOs to perform DB operations. Lets assume a situation where you have 3 DAO operations in a service method. If your 1st DAO operation failed, other two may be still passed and you will end up with an inconsistent DB state. Annotating Service layer can save you from such situations.

You are going to want your services to be transactional. If your DAOs are transactional, and you call different DAOs in each service, then you would have multiple transactions, which is not what you want. Make the service calls transactional, and all DAO calls inside those methods will participate in the transactions for the method.

i will suggest to put @Transactional in Service layer methods since we can have multiple DAO implementations. by using this we can made our services will be transactional. refer

best practice is to use A generic BasicService to offer common services.

The Service is the best place for putting @Transactional, service layer should hold the detail-level use case behavior for a user interaction that would logically go in a transaction. in this way we can have maintain separation between web application code and business logic.

There are a lot of CRUD applications that don't have any significant business logic, for them having a service layer that just passes stuff through between the controllers and data access objects is not useful. In these cases we can put transaction annotation on Dao.

So in practice you can put them in either place, it's up to you.

By having multiple calls in your service you need @Transactional in service. different calls to service will execute in different transactions if you put @Transactional in service.