IADCS Diploma Course
Distributed Programming with Java
U Nyein Oo
COO/Director(IT)
Myanma Computer Co., Ltd

Why Distributed Application?
Most of development and deployment

environments are Networked
Applications design to be distributed

(which is become necessary)
Process is distributed across multiple

networked computers
Implemented as Client/server Systems.

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Client/Server Systems?
Client requests resource from Server

Server accept the client’s request and

process and give result back to client
Typically there are three components in

client/server system.
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Three components of CSS
User Interface Layer( implemented by

application client like web browser)
Information Processing Layer( implemented

by application client/server/server support)
Information Storage Layer( implemented by

database server like web server,FTP server)
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IPL at Client Machine
Server Machine
Client Machine
User Information Information
Interface Processing Storage
Layer Layer Layer
(Web (Application (Application
Client) Server)
Browser)
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IPL at Server Machine
Client Machine Server Machine
User Information Information
Interface Processing Storage
Layer Layer Layer
(Web (Application (Application
Client) Server)
Browser)
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Different type of Method Invocation
Distributed Computing Environment(DCE)

Distributed Components Object

Model(DCOM)
Common Object Request Broker Architecture

(CORBA)
Java’s Remote Methods Invocation(RMI)

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Distributed Computing
Environment(DCE)
Industry standard of the OSF(Open Software

Foundation)
Vendor-neutral set of Distributed Computing

Provide security services to protect and

control access to data
Run of the major computing platforms and

designed to support distributed application
Key Technology for security,www and

Distributed Objec
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How Distributed Systems work?
Organized into cell(which is nothing but a

group of processing resources,services and
users that support a common function and
share a common set of DCE devices)
For example …separate department in a

company like(admin,finance..ect)
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The services and Technologies used
within DCE Cell
Directories Service

Distributed File Service(DFS)

Distributed Time Service(DTS)

Security Service

Remote Procedure Calls(RPC)

DCE Threads

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What is a DCOM?
Distributed Component Object Model

Product of Microsoft Corporation

Started with OLE technology that used to

support compound documents.(one that is
product of multiple application)
COM is solution for OLE and different from

DCE in its design approach.
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DCOM(cont)
COM is object oriented whereas DCE is

procedural oriented
A model ,programming Language can be

used COM to create distributed application
DCOM allows a COM object on one

computer to access methods of another
COM object on some other computers.
The remote object is accessed the same

manner as the local object.
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DCOM(cont)
DCOM is distributed COM over multiple

computers.
Local Object invokes the methods of Local

COM library of the remote object it is trying to
access.
COM library process the functions calls using

COM runtime
COM Runtime communicate using Object

RPC
The most important feature is application

security is based on Windows NT Policy. 13
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CORBA
Common Object Request Broker Architecture

Most popular architecture for building

distributed object oriented application
Is open standard not tied to particular vendor

Objects are accessible via ORBs

The client interface to ORB is written by

IDLKnown as IDL stub
The Server interface to ORB is IDL Skeleton

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Method invocation in CORBA
Client Host Server Host
client Server
Object Object
IDL IDL
Stub Skeleton
ORB
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Benefits using CORBA
Open standard and works on all platforms

Both clients and servers can be distributed

Language independent

Just have to provide IDL interface to object

An international standard and recognized by

most of software vendors.
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Why Java Distributed Object Model
Need?
TCP Socket is big Overhead

DCE ‘s RPC does not gel with Java OODA.

DCOM has good performance for Windows

and does not support java object fully.
CORBA is excellent but Java programmer

will have to learn IDL to develop DJA.
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RMI (your best choice for java)
JavaSoft design for Object oriented

distributed pure java application.
RMI also need client stub & server skeleton

Support seamless remote invocation on

objects in different VMs.
Support callbacks from server to applets.

Integrated DO model into Java Language

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RMI(cont;)
Make differences between DO model and

Local Java Object model apparent.
Writing reliable distributed applications as

simple as possible.
Preserve the type-safety provided by the

Java Runtime Environment
Save Java environment provided by security

managers and class loaders.
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RMI Architecture
JDOM is simply extension of JOM

Objects interact each other within same JVM

in Java’s Object Model
Objects interact with an object in another

JVM at Java Distributed Object Model
Client Object(local object) does not reference

directly on Server Object(remote object) and
references a remote interface
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Advantages using Remote Interface
Allows server objects to differentiate between

their local and remote interface
Present different access modes

No need to have server class file at the

compilation of client objects
RMI follow like CORBA except ORB

RMI Setup the Remote Reference Layer

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Three tier Architecture of Java RMI
Client Server
Object Object
Stub Skeleton
Remote Reference Layer Remote Reference Layer
Transport Layer Transport Layer
Lower Layer Protocols Lower Layer Protocols
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Inside RMI
Explain java.rmi packages:

– java.rmi
– java.rmi.registry
– java.rmi.server
– java.rmi.activation
– java.rmi.dgc
Three tiered layering of Java RMI

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java.rmi Package
This package provides the remote interface

It does not have any methods

It supports the following classes:

MarshalledObject class
–
Naming class
–
RMISecurityManager class
–
It defines exceptions such as RemoteException

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java.rmi.registry Package
This package provides classes and

interfaces for remote registry
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java.rmi.server Package
This package implements remote stubs and skeletons

It is also used to support RMI communications

It consists of the following classes:

RemoteObject class
–
RemoteServer class
–
RMILoader class
–
Operation class
–
LogStream class
–
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java.rmi.activation Package
This package is used to activate remote objects, when needed

It consists of the following classes:

Activable class
–
ActivationDesc class
–
getClassName( )

getCodeSource( )

getData( )

getGroupID( )

getRestartMode( )

ActivationGroup class
–
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java.rmi.dgc Package
This package provides classes and

interfaces that the RMI distributed garbage
collector uses
The server side of the distributed garbage

collector uses this package
It has two methods, dirty( ) and clean( ),

which indicate that the client has referenced
a remote object, and that the remote
reference has been completed, respectively
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Three Tiered Layering of Java RMI
The client object evokes the methods of stub

The stub uses the remote layer to communicate with the

skeleton
The remote layer uses the transport layer to establish the

connection between local and remote server
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Implementing RMI
Implementing RMI involves two steps

namely:
– Implementing RMI on Remote Host
– Implementing RMI on Local Host
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Implementing RMI on Remote Host
Step 1

Create a remote interface:
This has to be public and must extend the Remote interface
–
This method must throw RemoteException
–
Step 2

Create a class that implements the remote interface:
This class should create and initialize the remote object
–
It should implement all the methods defined in the remote
–
interface
There should be a main( ) method that will be executed as a
–
remote class
This main( ) method should also take care of security using the
–
setSecurityManager( ) method
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Implementing RMI on Remote Host
(Contd…)
Step 3

Create stub and skeleton classes using the rmic command.
Step 4

Copy the remote interface and stub file to the client host.
Step 5

Start the Remote Registry Server using the command start
rmiregistry.
Step 6

Execute the program using the java command to create an
object of class. This class registers itself with the remote
registry
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Implementing RMI on Local Host
Once RMI is implemented on the remote host, the

remote server is up and running
Create a client program to remotely invoke the

method of the object, and display the results
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Genreation Remote Interface
//remote interface
import java.net.*;
import java.security.*;
import java.rmi.*;
public interface MyServer extends
java.rmi.Remote{
String getAndSetMessage(String message)
throws java.rmi.RemoteException;
}
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Generation Client RMI
import java.rmi.RMISecurityManager;
import java.rmi.Naming;
import java.net.*;
import java.security.*;
public class MyClient{
public static void main(String args[]){
System.setSecurityManager(new RMISecurityManager());
try{
MyServerser=(MyServer)Naming.lookup(\"//147.81.10.2/ServerTest\");
String serverString=ser.getAndSetMessage(\"I amd Trying \");
System.out.println(\"reply from the server is \"+serverString);
}catch(Exception e){
System.out.println(e);
}
}
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Generation Server RMI
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.security.*;
import java.net.*;
public class MyServerImpl extends UnicastRemoteObject implements MyServer{
static String hostName=\"147.81.10.2\";
String name;
public MyServerImpl(String name) throws RemoteException{
super();
this.name=name;
}
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Generation Server RMI (cont)
public String getAndSetMessage(String message)throws RemoteException{
return(\"My name is \"+name+\"Thanks for message\"+message);
}
public static void main(String args[]){
System.setSecurityManager(new RMISecurityManager());
try{
String objectname=\"Servertest\";
MyServerImpl theServer=new MyServerImpl(objectname);
Naming.rebind(\"//\"+hostName+\"/\"+objectname,theServer);
System.out.println(\"I am Registered\");
}catch(Exception e)
{
System.out.println(e);
}
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Steps to Compilation
Compilation Remote Interface File

(same as regular .java file)
Compilation Remote Client File

(same as regular .java file)
Compilation Remote Server File

I.same as regular .java file
II. User rmic compiler to create stub and skeleton
class files like
c:\\jdk1.3.1\\bin>rmic MyServerImpl
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Steps to Compilation(cont)
Starting rmi registry

>start rmiregistry
 Run as follow
>java –Djava.security.policy=policy
MyServerIMpl
 Edit policy for permission grant
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Example-2(Remote Interface)
//Remote Interface
import java.rmi.*;
import java.net.*;
public interface Server1 extends Remote {
public void doSomething()
throws RemoteException; }
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Client Remote
import java.rmi.*;
import java.net.*;
import java.rmi.server.*;
public class Client1 {
public static void main(String[] args) {
System.setSecurityManager(new RMISecurityManager());
try {
Server1 ro = (Server1)Naming.lookup(\"doSomething\");
System.out.println(\"Location: \"+System.getProperty(\"LOCATION\"));
ro.doSomething();
} catch (Exception e){
e.printStackTrace();
System.exit(-1);
}
}
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}

Server Remote
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
public class Server1Impl extends java.rmi.server.UnicastRemoteObject
implements Server1 {
public static void main(String[] args) {
System.setSecurityManager(new RMISecurityManager());
try {
Server1Impl obj = new Server1Impl();
Naming.rebind(\"doSomething\", obj);
System.out.println(\"doSomething bound in registry\");
} catch (Exception e) {
e.printStackTrace();
return;
}
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Server Remote (cont)
public Server1Impl() throws RemoteException { }
public void doSomething() throws RemoteException {
System.out.println(\"This message is printed by the Server1
object\");
System.out.println(\"Location: \" +
System.getProperty(\"LOCATION\"));
}
}
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Invoke rmi registry & Run Client
Remote
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Running Remote Server
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