Interface implementation launches different exceptions

Question

I have an interface

public interface DataDAO {
     public void doSomething() throws Exception;
}

Lets say that there are two implementations, one that uses Database to get the data and another one that uses a Webservice.

public class DataDAOJdbc implements DataDAO {
    public void doSomething() throws Exception {
         //Implement
    }
}

public class DataDAOWebService implements DataDAO {
    public void doSomething() throws Exception {
         //Implement
    }
}

As you can already see, the problem is the super generic exception launched. As both implementations need to raise the same kind of exception.

The Jdbc implementation really only raises lets say SQLException while the Webservice implementation only rises the IOException.

Question is, how can I make the interface more elegant, so I capture a proper exception?

The first thing that I though was creating my own exception, and declare it on the interface level

public interface DataDAO {
  public void doSomething() throws MyCoolException;
}

And then, of course implement accordinly.

Question is, does this make sense? I have never created my own exceptions, so I am not really sure if this makes much sense or not. Also, what should I take into account when creating MyCoolException?

Answer 1

The first thing that I though was creating my own exception, and declare it on the interface level (...) does this make sense?

Yes, it does makes sense and I would think it is the best way to handle these situations.

I'll provide a kickoff example for this (based on your current code):

public class MyCoolException extends Exception {
    public MyCoolException() {
    }
    public MyCoolException(String message) {
        this.message = message;
    }
}

public interface DataDAO {
    public void doSomething() throws MyCoolException;
}

public class DataDAOJdbc implements DataDAO {
    public void doSomething() throws MyCoolException {
         //Implement
         try {
         } catch (SQLException e) {
             //handle the exception
             logger.error("Error!", e);
             //throw your custom exception
             throw new MyCoolException(e.getMessage());
         }
    }
}

public class DataDAOWebService implements DataDAO {
    public void doSomething() throws MyCoolException {
         //Implement
         try {
         } catch (IOException e) {
             //handle the exception
             logger.error("Error!", e);
             //throw your custom exception
             throw new MyCoolException(e.getMessage());
         }
    }
}