Notes

Server STUB
Middleware on client side. A proxy intercepting client calls and invoking remote server method by sending request in a stream.

Serve SKELETON
Receive Client stream with method and data. Disassembles, invokes method and refuses data. The roles of STUB and SKELETON swap.

RMI Registry
• A utility app which registers remote object and provides services by mapping names(strings) to binary reference to servant object
• Resides typically on server host but can be on another host (on server side)
• Runs as a background process – windows C:>start.rmiregistry – to run a background process
• Solaris/Linus - $rmiregistry &
Functionality
 Server app registers servant object by symbolic name and corresponding ref to constructed object.
 Client looks up RMI Registry by symbolic name and receives (In java 5.0 and higher) a stub.
o Rem: Previous reversion of JAVA required compiler to generate STUB as linkable model.
Server side activity
Examples refer to Robot case study
Server application
1.Constructs Servant Object
Robot rbt = new Robot(0,0);
2. Registers servant with rmiregistry
 Either using rebind() method (of registry object)
 Or Naming.rebind() static method
Parameters
Naming.rebind(“Remote Robot”, rbt)
Registry on Local Host, on port 1099
Or Naming.rebind(“rmi://cis.um.edu.mt:3056/RemoteRobot”,rbt)

3. Run the ServerApp .exe with security setup
Either on communication line or security policy file.

Activity on Java version < 1.5 (older)
After point 1
2. Create Stub and Skeleton
C:>rmic Robot
Rmic.exe compiler – Robot class

Results in:
Robot_Strub.class
Robot_skeleton.class

Development of ServerApp application hosting Robot Servant
1. Create Remote interface
Interface IMotion extends Remote{
Prescribes 3 methods
}

Implement Servant Robot
Public class Robot(int x, int y) throws RemoteException()
{
This.x = x;
This.y = y;
}
Public void start(){
-------
-------
}
Public void stop(){
}
Public void moveTo(new X, new Y){
}
3. ServerApp.java (main program)
{
Public static void main(String [] args)
{…setup security
Robot rbt = new Robot(0,0);
Naming.rebind(“RemoteRobot”,rbt);
}
}

Launching rmi registry
C:>rmiregistry
Lanching server app
C:>java ServerApp

NOW SERVER IS RUNNING

Structure of Client app
Class Client{
Public Client(){
Security using RMISecurityManager(){
Public static void main(String [] args) throws RemoteException
{ IMOtion remObj = (IMotion)Naming.lookup(“RemoteRobot”);
remObj.start();
remObj.Moveto(20,30);
}

Notes on RMI Security
Reason for security: Allow only legitimate clients to access remote server and avoid access to clients from unknown intruders
1. Set System to RMI Security policy file (ref to Java RMI T1-2)
2. Content of RMI Security.policy file
Grant { permission .. specific permissions
Examples: grant { permission java.security.AllPermissions; .. full access
Grant java.net.SocketPermission “* 1099”,”connect.resolve”;
Grant java.net.SocketPermission, “*:2050”, “connect.resolve”;

Use of RMI Technology
Used as a proprietary distributed system serving only one company with several remote branches. Normally it is not publicly available.

IV – Web Services Technology
Nowadays popular technology providing services to the right public using internet infrastructure can be licenced frequently.

Features:
Web Servies is a remote application accessible on the Internet via http protocol allowing:
1. Simple (user-friendly) discovery from web browsers
2. Transparent way of data and services description (using XML)
3. Transparent way of data referencing remote objects using native programming language ( through PROXY).