Java Coding Question And Answers

Defining and Exporting a Remote Object

1. Define the remote interface.
import java.rmi.*;
public interface RObject extends Remote {
void aMethod() throws RemoteException;
}

Looking Up a Remote Object and Invoking a Method
try {
// Look up remote object
RObject robj = (RObject) Naming.lookup(//localhost/RObjectServer");
// Invoke method on remote object
robj.aMethod();
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
}

Passing Parameters to a Remote Method

Arguments to remote methods must be primitive, serializable, or Remote. This example demonstrates the declaration and use of all three parameter types.

1. Define the remote interface.

import java.rmi.*;
public interface RObject extends Remote {
// This parameter is primitive.
void primitiveArg(int num) throws RemoteException;
// This parameter implements Serializable.
void byValueArg(Integer num) throws RemoteException;
// This parameter implements Remote.
void byRefArg(ArgObject arg) 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 void primitiveArg(int num) throws RemoteException { }
public void byValueArg(Integer num) throws RemoteException { }
public void byRefArg(ArgObject arg) throws RemoteException {}
}

3. Compile the remote object implementation.
> javac RObject.java RObjectImpl.java

4. Generate the skeletons and stubs.
> rmic RObjectImpl

5. Create an instance of RObjectImpl 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 and pass the parameters.

try {
// Look up the remote object
RObject robj = (RObject) Naming.lookup("//localhost/RObjectServer");
// Pass a primitive value as argument
robj.primitiveArg(1998);
// Pass a serializable object as argument
robj.byValueArg(new Integer(9));
// Pass a Remote object as argument
robj.byRefArg(new ArgObjectImpl());

} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
}