我们能否在不影响服务层的情况下处理从dao层到表示层的异常（服务层中没有任何修改）

Question

The scenario is like I wrote a MVC-based application: Controller - Service - DAO layer. Now I got an exception in DAO layer and I want to handle that exception in presentation layer so that service layer needs no change.

Because by using regular try/catch or throws it has to pass through the service layer which I don't want.

Is there any better approach to achieve it?

class Controller{
  method1(){}
}

class service(){
  method1Serice(){}
}

class DAO(){
  method1DAO(){
  // exception occurs here
}

Answer 1

You can have the DAO class throw an unchecked exception. (any subclass of RuntimeException will do). You can create your own custom exception or use any of the predefined ones. just make sure the Service doesn't catch Throwable and you can have the Controller catch it.

Answer 2

You can extend your exception class from RuntimeException so that compiler does not complain about exception handling. You can then catch that exception in the presentation layer.

Answer 3

Perhaps you are looking for Controller Based Exception Handling , you can check these in Exception Handling in Spring MVC and also Error Handling for REST with Spring .

@ExceptionHandler(YourException.class)
public String handleException(){
    logger.info(message);
    return "database_error";
}

Actually I would suggest you handle the exceptions properly in Service-Layer and encapsulate that exception properly to return to the front-user via Controller-Layer .

Normally, checked exceptions are carrying some meaningful messages which can be used to do recovery or let the caller explicitly handle it properly. Try not to directly avoid it since it's there.

Answer 4

As I understand it, a data access object (DAO) is intended for transferring data between the server and the client. I'm assuming that the client is what you refer to as the presentation layer . In other words, the part that the end user interacts with. As such, the DAO should contain fields and accessor methods only, ie it should not contain logic. Hence it should not contain methods that may throw exceptions. So I would suggest perhaps re-designing your application. Otherwise, perhaps you can provide more detailed code?