RMI and RemoteException

[Roel De Nijs]

Hi,

A little bit playing around with RMI. I have the following (simple) interface:

public interface PowerService extends Remote {
	public BigInteger square(int number) throws RemoteException;
}

and an implementation that's even simpler:

   
public class PowerServiceServer extends UnicastRemoteObject implements PowerService {
	private static final long serialVersionUID = 1L;

	public PowerServiceServer() throws RemoteException {
		super();
	}

	public BigInteger square(int number) throws RemoteException {
		BigInteger bi = new BigInteger(String.valueOf(number));
		return bi.multiply(bi);
	}
}
 

I was wondering if it's possible to work with RMI but in your implementation get rid of the RemoteException, so something like:

public interface PowerService {
	public BigInteger square(int number) throws ServiceException;
}

and an implementation:

public class PowerServiceServer extends UnicastRemoteObject implements PowerService, Remote {
	private static final long serialVersionUID = 1L;

	public PowerServiceServer() throws RemoteException {
		super();
	}

	public BigInteger square(int number) throws ServiceException {
		//...
	}
}

so you could use the same interface for a local implementation, another network technology,... or are you stuck on this RemoteException?

Kind regards,
Roel

[Oscar Costa]

Hello Roel,

You can use an application exception too. But you need to throw the RemoteException. This exception is used when a remote method invocation fails...

See at http://java.sun.com/j2se/1.5.0/docs/guide/rmi/spec/rmi-objmodel5.html

[Roel De Nijs]

Oscar,

Thanks for your quick reply.

after some experimenting following conclusions:
- PowerService without "extends Remote" --> ClassCastException when trying to run the client
- method from PowerService without "throws RemoteException" --> RemoteException("remote object implements illegal remote interface") when trying to run the server

so it's required to add RemoteException to all of your method signatures in your interface. The best you can do to depend as little to rmi as possible, is having something like this:

public interface PowerService {   
    public BigInteger square(int number) throws RemoteException, ServiceException;   
}
public interface RemotePowerService extends Remote, PowerService {   
}
public class PowerServiceServer extends UnicastRemoteObject implements RemotePowerService 
    public PowerServiceServer() throws RemoteException {   
        super();   
    }   
  
    public BigInteger square(int number) throws RemoteException, ServiceException {   
        BigInteger bi = new BigInteger(String.valueOf(number));   
        return bi.multiply(bi);   
    }   
}