What we have to say on client:

remoteObject = ObjectBroker.lookup("global name");

result = remoteObject.method(parameter);

What we have to say on server:

remoteObject = new RemoteObject();

ObjectBroker.register("global name", remoteObject);

• A server application is responsible for containing instances of remote objects
• The server uses a naming service to publish means of access to its remotely accessible objects
• Java RMI has a simple naming service called rmiregistry
• The compiler for stubs and skeletons is called rmic. Stubs and skelletons are generated automatically in later versions

• Has same syntax as local method invocation but different semantics
• Objects to be made remote must have an interface derived from the Remote interface
• All methods declared by the interface must throw RemoteException
• These methods can use both ordinary and remote objects as arguments/results

public interface RemoteThingInterface extends Remote {

       public String method() throws RemoteException;

}

Class of a remote object must extend UnicastRemoteObject or another subclass of RemoteObejct

public class RemoteThing extends UnicastRemoteObject

         implements RemoteThingInterface {

public RemoteThing() throws RemoteException  {

         super(); }

...

}

• The binder for JavaRMI is called RMIregistry
• an instance of RMIregistry normally runs on every Servery machine
• Methods of the Naming class (bind, rebind, unbind lookup) used to access the RMIregistry

public class RemoteTHingServer {

  public static void main (String [] args) {

    try { RemoteThing remoteThing = new RemoteThing();

      Naming.rebind("remoteThing", remoteThing);

    } catch 

    ...

}

public class RemoteThingClient {

  public static void main(String[] args) {

    try {

      RemoteThingInterface = remoteThing = 

        (RemoteThingInterface) Naming.lookup(

           "rmi://localhost/remoteThing");

       ...

• Both ordinary and remote objects used as method arguments/results
• remote interface used to declare argument/result type
• Serialization used for marshaling arguments and results
• Remote objects are passed as remote object references
• non-remote objects are copied and passed by value

• Information about the class (name, version number) of each object included
• Values of primitive types are converted into binary format
• Remote objects are serialized by copying their remote reference
• Serializing objects involves serializing all objects they refer to
• Must implement serializable interface

• It is possible to organise that a server is activated only when an object for which it is responsible is accessed
• The object will then be reconstructed from a file
• Java RMI supports this (Through the Activatable class), but this is beyond the scope of this module

Storing objects in databases in order to avoid state loss of remote objects if the server goes down

Objects stored in persistent object store will be activated when their methods are invoked by other objects

• Will remove objects from memory once no other object in the system holds a reference to it
• Java's based on reference counting
• References to proxies of a remote object are counted on each client process
• Server processes maintain a list of client processes holding references to its remote objects
• Clients inform server of changes

• Used for distributed garbage collection
• References to proxies of a remote object are counted on each client process
• Server processes maintain a list of client processes holding references to its remote objects
• Clients inform server of changes