How to Make a Java RMI Call via Internet to a Server

Question

I tried a simple java rmi program where the client makes a remote call to a server and the server returns a String. it worked perfectly with two computers connected via lan. how can i implement a remote call by a client which is not connected to the server via lan but the server and client are both connected to the internet? I tried the following simple code by changing 'localhost' in Client.java to server's ip address. Didn't Work. what do i need to make such a remote call?

//Remote Interface -> MyInterface.java

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

public interface MyInterface extends Remote
{
    public String SaySomething() throws RemoteException;
}

//Client.java

import java.rmi.*;
import java.rmi.registry.*;

public class Client
{
    public static void main(String []args)
    {
        System.setProperty( "java.security.policy", "client.policy" );
        if (System.getSecurityManager() == null)
                    System.setSecurityManager(new RMISecurityManager());
        try {
                        String name = "MyInterface";
                        Registry registry = LocateRegistry.getRegistry("localhost",4501);
                        MyInterface mi = (MyInterface) registry.lookup(name);
            System.out.println(mi.SaySomething());
                } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

//Server.java

import java.rmi.*;
import java.rmi.registry.*;
import java.rmi.server.UnicastRemoteObject;

public class Server implements MyInterface
{
    public Server()
    {
        super();
    }
    public String SaySomething()
    {
        return "Server Speaking";
    }
    public static void main(String []args)
    {
        System.setProperty( "java.security.policy", "server.policy" );
        if(System.getSecurityManager() == null)
           System.setSecurityManager(new RMISecurityManager());
            try {
                        String name = "MyInterface";
                        MyInterface mi = new Server();
                        MyInterface stub =(MyInterface) UnicastRemoteObject.exportObject(mi,4501);
                        Registry registry = LocateRegistry.createRegistry(4501);
                        registry.rebind(name, stub);
                        System.out.println("Server bound");
            } catch (Exception e) {
            System.out.println("oops");
                }
    }
}

I get the following exception: java.security.AccessControlException: access denied ("java.net.SocketPermission" "x.x.x.x:4501" "connect,resolve") at java.security.AccessControlContext.checkPermission(AccessControlContext.java:366) at java.security.AccessController.checkPermission(AccessController.java:555) at java.lang.SecurityManager.checkPermission(SecurityManager.java:549) at java.lang.SecurityManager.checkConnect(SecurityManager.java:1051) at java.net.Socket.connect(Socket.java:574) at java.net.Socket.connect(Socket.java:528) at java.net.Socket.(Socket.java:425) at java.net.Socket.(Socket.java:208) at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:40) at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:146) at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:613) at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:216) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202) at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:340) at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source) at Client.main(Client.java:14)

It would help if you provided more details about how it failed... "didn't work" is a bit too vague. Also, what have you tried to solve or investigate the problem? — cjstehno
I would add that RMI is not a secure protocol. So please don't go around sending credit card details :). — Augusto
Sorry, I am a little rusty with port numbers but isn't 4501 too low for general over-the-internet use, I thought that ports below a certain number were reserved. Maybe try a higher port like 10101 or something. — cjstehno
grant { permission java.security.AllPermission; }; Both for client and server — user1717415

user207421 user207421 · Accepted Answer · 2013-07-10T01:12:28

Unless you're using the codebase feature you don't need the security manager for RMI. Remove it.

How to Make a Java RMI Call via Internet to a Server

2 Answers