Remote methods

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1. The
   remote interface must be
   public
   (it cannot have “package access,” that is, it cannot be
   “friendly”). Otherwise, a client will get an error when attempting
   to load a remote object that implements the remote interface.
2. The
   remote interface must extend the interface java.rmi.Remote.
3. Each
   method in the remote interface must declare java.rmi.RemoteException
   in its
   throws
   clause in addition to any application-specific exceptions.
4. A
   remote object passed as an argument or return value (either directly or
   embedded within a local object) must be declared as the remote interface, not
   the implementation class.

//: PerfectTimeI.java
// The PerfectTime remote interface
package c15.ptime;
import java.rmi.*;
 
interface PerfectTimeI extends Remote {
  long getPerfectTime() throws RemoteException;
} ///:~ 

//: PerfectTime.java
// The implementation of the PerfectTime 
// remote object
package c15.ptime;
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.net.*;
 
public class PerfectTime
    extends UnicastRemoteObject
    implements PerfectTimeI {
  // Implementation of the interface:
  public long getPerfectTime()
      throws RemoteException {
    return System.currentTimeMillis();
  }
  // Must implement constructor to throw
  // RemoteException:
  public PerfectTime() throws RemoteException {
    // super(); // Called automatically
  }
  // Registration for RMI serving:
  public static void main(String[] args) {
    System.setSecurityManager(
      new RMISecurityManager());
    try {
      PerfectTime pt = new PerfectTime();
      Naming.bind(
        "//colossus:2005/PerfectTime", pt);
      System.out.println("Ready to do time");
    } catch(Exception e) {
      e.printStackTrace();
    }
  }
} ///:~ 

1. Create
   and install a security manager that supports RMI. The only one available for
   RMI as part of the Java distribution is RMISecurityManager.
2. Create
   one or more instances of a remote object. Here, you can see the creation of the
   PerfectTime
   object.
3. Register
   at least one of the remote objects with the RMI remote
   object registry for bootstrapping purposes. One remote object can have methods
   that produce handles to other remote objects. This allows you to set it up so
   the client must go to the registry only once, to get the first remote object.

Setting
up the registry

1. localhost
   does
   not work with RMI. Thus, to experiment with RMI on a single machine, you must
   provide the name of the machine. To find out the name of your machine under
   32-bit Windows, go to the control panel and select “Network.”
   Select the “Identification” tab, and you’ll see your computer
   name. In my case, I called my computer “Colossus” (for all the hard
   disks I’ve had to put on to hold all the different development systems).
   It appears that capitalization is ignored.
2. RMI
   will not work unless your computer has an active TCP/IP
   connection, even if all your components are just talking to each other on the
   local machine. This means that you must connect to your Internet service
   provider before trying to run the program or you’ll get some obscure
   exception messages.

PerfectTime_Stub.class
PerfectTime_Skel.class

//: DisplayPerfectTime.java
// Uses remote object PerfectTime
package c15.ptime;
import java.rmi.*;
import java.rmi.registry.*;
 
public class DisplayPerfectTime {
  public static void main(String[] args) {
    System.setSecurityManager(
      new RMISecurityManager());
    try {
      PerfectTimeI t =
        (PerfectTimeI)Naming.lookup(
          "//colossus:2005/PerfectTime");
      for(int i = 0; i < 10; i++)
        System.out.println("Perfect time = " +
          t.getPerfectTime());
    } catch(Exception e) {
      e.printStackTrace();
    }
  }
} ///:~