Exeception handling

# What are the best practices to handle exception at Controller, Service and DAO Layer simultaneously in Spring & Hibernate

    You should not handle exception at DAO layer. Reason: Normally we place @Transactional annotation at Service Layer. 
    hence we need to rollback transaction at service layer. If you handle exception at DAO then it will not rollback.
    Follow below link to know why we should place @Transaction at Service Layer.

  Where should "@Transactional" be placed Service Layer or DAO You should not handle exception at Service Layer. 
  Reason: As service layer execute multiple DAO for DB operation and we need to rollback transaction if any DAO fails. 
  If we handle exception in service then we may not rollback transaction. There is manual approach for rollback transaction but it is not recommend.
  TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();

#So handle exception in controller layer.

  you don't handle exceptions at all levels of your application simultaneously; you have to consider their contextual meaning and
  what the appropriate strategy is for your application. Some errors should be ignored, some should be wrapped, some should be allowed to be raised directly.

  One method for dealing with exceptions in a spring-mvc application is to wrap fatal errors from the underlying libraries with your own where appropriate, 
  named for the level at which they are thrown, e.g. ServiceException or RepositoryException. A @ControllerAdvice-annotated class can then handle
  these errors with @ErrorHandler-annotated methods and return 5XX http errors.

  Common application errors, like an entity not being found due to an incorrect id can result in a custom exception, 
  e.g. NotFoundException being raised and subsequently caught in your @ControllerAdvice-annotated class.

  The advantage to this technique is that you have less error-handling code in your different application layers and can 
  centralize the conversion of exceptions to responses.

    You should make your services transactional and handle the exceptions in the Controller layer: you may choose Controller 
    Based Exception Handling (Using @ExceptionHandler) or Global Exception Handling (Using @ControllerAdvice Classes). 
    It may be practical to display something, e.g. an error page to users in case of exceptions.