Question

I’m using RMI to allow access to my Java application via MATLAB, which runs in another JVM. MATLAB has a nice interface to print the methods of a Java object. But it fails with RMI, because the object it gets is a proxy.

So I would like to add my own method to extract/print the capability of a remote interface (RMI obviously can’t directly access methods not available in exported remote interfaces).

How could I do this with reflection, either on the client end of the RMI connection, or on the server end? I don’t have much experience using reflection. Use case below.

edit: what I’m getting most stuck on is given an arbitrary object X (including where X is an RMI proxy), how can I use reflection to obtain the interfaces implemented by that object?

java classes:

/** client-side remote describer */
class RemoteDescriber
{
    RemoteDescription describe(Remote remote) { ... }
}

/* representation of remote interfaces implemented by an object */
class RemoteDescription implements Serializable
{
    /* string representation of remote interfaces implemented by an object */
    @Override public String toString() { ... }

    /* maybe there are other methods permitting object-model-style navigation
     * of a remote interface
     */
}

interface FooRemote extends Remote
{
    /* some sample methods */
    public int getValue() throws RemoteException;
    public void setValue(int x) throws RemoteException;
    public void doSomethingSpecial() throws RemoteException;
    /* other methods omitted */        

    /** server-side */
    public RemoteDescription describe() throws RemoteException;        
}

and sample client session in MATLAB

x = ...;     % get something that implements FooRemote
describer = com.example.RemoteDescriber;
% describer is a client-side Java object

description1 = describer.describe(x)

%%% prints a description of the FooRemote interface 
%%% obtained by the client-side RemoteDescriber

description2 = x.describe()

%%% prints a description of the FooRemote interface 
%%% obtained on the server-side by x itself, and marshalled
%%% to the client

Answer 1

The objects on your client are proxies: they are called stubs. To get the interfaces from it you should code something like this, where o is your object:

Class c = o.getClass();
Class[] theInterfaces = c.getInterfaces();
for (int i = 0; i < theInterfaces.length; i++) {
   String interfaceName = theInterfaces[i].getName();
   System.out.println(interfaceName);
}

Stubs are auto-generated: therefore you should not implement something into them, but you could implement a method getInformation() in your remote interfaces; every server object should implement this and return a string which contains all information of the server object. This method generates the string by getting information via reflection from the this object.