通过 RMI 传输对象的数据（特别是服务器变量）

Question

Edit : The Java™ Tutorials say that

the server and the client communicate and pass information back and forth

and that RMI

provides mechanisms for loading an object's class definitions as well as for transmitting an object's data.

I was hoping that "an object's data" would include a server object's variables (such as Test.value in my code, below) - but the first comments I got indicate that perhaps I was wrong. My original question follows.

I am trying to access a remote object that I am sending over RMI to a client. I am only able to access its methods, but not its instance variables - I get the interface's fields instead. My question is, once I implement and instantiate a class on a server, how do I access its [public] fields, without using getters? I am able to send a stub without any errors or exceptions, but like I said, I am not able to access the server's object's fields, only the interface's. Following is an abbreviated version of my interface, implementation, server, and client.

package test;

import java.rmi.Remote;
import java.rmi.RemoteException;

public interface TESTint extends Remote {

        double value = -22;
        String shortName = "TESTint";

        double getValue() throws RemoteException;
}
package test;

import java.rmi.RemoteException;

public class Test implements TESTint {

    public double value = -33;
    public String shortName = "TestAccount";
    public int whole = 1;

    public Test(String shortName) {
        this.shortName = shortName;
        print(shortName);
    }

    public double getValue() throws RemoteException {
        return value;
    }

    public void print(Object o) {
        System.out.println(shortName + ": " + o);
    }   
}
package test;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;

public class RemoteTestMain {
    Test test;

    public static void main(String[] args) throws InterruptedException {
        if (System.getSecurityManager() == null) { System.setSecurityManager(new SecurityManager()); }
        new RemoteTestMain();
    } // main

    public RemoteTestMain() {
        test = new Test("Charlie");
        Registry registry;
        try {
            registry = LocateRegistry.createRegistry(1234);
            registry.list( ); // will throw an exception if the registry does not already exist         
            print(test.shortName); // it gets it right here
            print(test.value); // it gets it right here
            TESTint r = (TESTint) UnicastRemoteObject.exportObject(test, 0);
            registry.rebind("DCregistry", r);
            print("test bound");  
        } catch (java.rmi.RemoteException ex) {
            print("Remote Exception at Server");
            ex.printStackTrace();;
        }
    }

    public static void print(Object o) {
        System.out.println("Server: " + o);
    }
}
package test;

import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;

public class Client {
    TESTint test;

    public static void main(String[] args) {
        try {
            new Client();
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    } // main

    private void init(int account) {
        print("INITiating Account " + account);         
        try {
            Registry registry = LocateRegistry.getRegistry(1234);
            test = (TESTint) registry.lookup("DCregistry");
        } catch (Exception e) {
            System.err.println("RMI exception:");
            e.printStackTrace();
        }
        print("Short name : " + test.shortName);
        print("value: " + test.value);
        try {
            print("Value through getter is " + test.getValue());
        } catch (RemoteException e) {
            print("Could not get equity");
            e.printStackTrace();
        }
    } // init(int account)

    public Client() throws RemoteException { 
        if (System.getSecurityManager() == null) { System.setSecurityManager(new SecurityManager()); }
        init(2);
    }

    private static void print(Object o) {
        System.out.println("GUI: " + o);
    }
}

PS In the Client code above, test.shortName is wiggly-underlined and Eclipse suggests that The static field TESTint.shortName should be accessed in a static way . I understand that the Client does not recognize the implementation, only the interface - but is there a way to access test's fields, not only its methods? I have many fields in my original code and I do not want to write getters for each and every one, if possible.

Answer 1

RMI stands for Remote Method Invocation which means that you can remotely execute a method of an object. The implementation of the method resides in the remote system. You can never access the instance variables of the implementation class which exists in the remote system even if they are public. You can only execute public methods which are exposed by the Inteface. So if you want to access the variables, you need add public gettter methods both in the Inteface and implementation class.