Returning Values from a Remote Method

Return values from remote methods must be primitive, serializable, or implement Remote. This example demonstrates the declaration and use of all three return types.

1. Define the remote interface.

import java.rmi.*;

public interface RObject extends Remote {
    // This return value is primitive.
    int primitiveRet() throws RemoteException;

    // This return value implements Serializable.
    Integer byValueRet() throws RemoteException;

    // This return value implements Remote.
    ArgObject byRefRet() throws RemoteException;
}

public interface ArgObject extends Remote {
    int aMethod() throws RemoteException;
}
2. Define the remote object implementation.
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

public class RObjectImpl extends UnicastRemoteObject implements RObject {
    public RObjectImpl() throws RemoteException {
        super();
    }
    public int primitiveRet() throws RemoteException {
        return 3000;
    }
    public Integer byValueRet() throws RemoteException {
        return new Integer(2000);
    }
    public ArgObject byRefRet() throws RemoteException {
        return new ArgObjectImpl();
    }
}
3. Compile the remote object implementation.
> javac RObject.java RObjectImpl.java
4. Generate the skeletons and stubs.
> rmic RObjectImpl
5. Create an instance of the remote object and bind it to the RMI Registry.
try {
    RObject robj = new RObjectImpl();
    Naming.rebind("//localhost/RObjectServer", robj);
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (RemoteException e) {
}
6. Look up the remote object, invoke the methods, and receive the return values.
try {
    // Look up the remote object
    RObject robj = (RObject) Naming.lookup("//localhost/RObjectServer");

    // Receive the primitive value as return value
    int r1 = robj.primitiveRet();

    // Receive the serializable object as return value
    Integer r2 = robj.byValueRet();

    // Receive the Remote Object as return value
    ArgObject aobj =  robj.byRefRet();
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
}