corba by paul m. pse 2010 better

8/3/2019 CORBA by Paul M. PSE 2010 Better

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Paul I. Muntean CORBA 1

CORBA

Common Object Request Broker

Architecture

by Paul I. Muntean


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CORBA Overview

What is CORBA? Common Object Request Broker Architecture

Communication infrastructure for distributed objects

Allows a heterogeneous, distributed collection of objects tocollaborate transparently

What is CORBA good for?

Developing distributed applications

Locating remote objects on a network

Sending messages to those objects

Common interface for transactions, security, etc.


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CORBA Overview

Motivation for CORBA Computation is distributed

Scalability: multiprocessing

Take computation to data

Heterogeneous architectures

Users are distributed Multiple users interacting and communicating via distributed applications

Data are distributed

Administrative and ownership reasons

Heterogeneous systems

Shared by multiple applications Scalability


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Outline

Main Components of CORBA architecture

Broker Pattern short review

Get started with a basic CORBA application Exercises

Conclusion


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Main Components of CORBA

ORB Core

CORBA Objects

OMG Interface Definition Language (OMG IDL)

Stubs and Skeletons Dynamic Invocation Interface, Dynamic Skeleton Int.

Object Adapter (Portable Object Adapter)

Interface Repository

ORB Interoperability

Servant


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Common Object Request Broker Architecture

The ORB allows client

applications to find objects

and invoke methods on themlocally or across a network. It

handles passing requests,

responses and exceptions

between a client object and a

server object.

CORBA Objects avirtual entitycapable of beinglocated byan ORB and havingclient requestsdelivered to it.Can be instantiatedby one or moreServants.

Servants areprogramming

language entitythat exists in thecontext of a serverand containingcode that

implements aCORBA object.

The compiler used toobtain the IDL stubs fromthe IDL file

The client applicationis starting the requestto the server

Generated by the IDLCompiler.Stub handles themarshalling of a request,that is converting datastructure into wireformat.

Skeleton codetranslates wireformat datainto memorydata format

(unmarshaling)

The DII defines a requestso that clients who knowthe object reference andinterface type can buildrequests without having torely on the IDL generatedstub code.

Serves as the glue between CORBAObject implementation and the ORBitself. Request Demultiplexing

,Operation Dispatching , Activation anddeactivation , Generating ObjectReferences

Provides a dynamic mechanismfor CORBA-based applicationsto access OMD IDL type system

when it is executing.

Common Protocols to facilitatetransmission of CORBArequests and replies between

ORBs. GIOP, IIOP, ESIOP ,IOR.

The DSI deals with requests sentby clients in a generic manner.

Looks at the requested operationand its arguments and interpretingthe semantics dynamically.

IIOP is a high-level protocol that takes care of

many of the services associated with the levelsabove the transport layer, including data

translation, memory buffer management, dead-

locks and communication management. It is

also responsible for directing requests to the

correct object instance within an ORB.


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Outline


Broker Pattern short review


Conclusion


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Broker Pattern

Example taken from : Slide no. 48 of the lecture Architectural patterns 2 of prof. B Bruegge


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CORBA Architecture based on Broker PatternThe Stub receives callsfrom the client. It hasthe role of marshaling

parameters.

POA or Portable Object Adapter.Passes calls to requested object andmethod. It contains persistent or

transient Skeletons .

Diagram adapted from the lecture Architectural patterns 2 of prof B. Bruegge.

The Naming Service provides the principal mechanism through which most

clients of an ORB-based system locate objects that they intend to use (make

requests of). It is located in the ORB box as one of the services of it.

ORB Core it is like the bridge inthe Broker Pattern .It has the roleof communication with ORB slocated on other machines.

ORB or Object RequestBroker. Used for

communication betweenclient and server.

Th

e skeleton is responsiblefor calling methods on theServant and Unmarshals

parameters for the Servant.


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Outline


Broker Pattern Short review


Conclusion


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Communication between the Client and Server

Communication between the Client and Server

1. Th

e client calls th

e service sayh

ello of th

e server.2. The ORB transmits the call to the servant-object, he must be activated.

3. The service say hello of the server will be started and delivers an string as a parameter.

4. The ORB transmits this string back to the client.

5. The clients prints this string on his console.


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Steps needed for creating and running a CORBA

application

1. Writing of the IDL file.

2. Write the client application.

3.W

rite th

e server application.4. Compile the two applications and start the server.

5. Run the client.

Example taken from :http://www.nt.fh-koeln.de/fachgebiete/inf/diplom/corba/html/kompilieren.html


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Writing the IDL file

Step 1:Descriptio

n of theCORBA

IDL-Module

Start a text editor and save afterwards the file with the followingname Hello.idl.

Write in the file :module HelloApp {//code };

Save the file.

Step 2:Interfacedeclaratio

n

Here we write our own interface. Replace the text //code from theprevious example with the following.interface Hello{//code 2};

Save again the file

After using the IDLJ compiler the result will be a bunch of java fileswhich will be implemented by the client and server.

Step 3:Method

declaration

The methods describe the behavior of the services which theserver is offering. We have in our example the service sayHello().Insert in your code: string sayHello(); instead of //code2

Hello.idl file is now complete.


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Running the IDLJcompiler

1.1 Be sure that the path where you have theIDLJcompiler is inthe CLASSPATHelse add it.

1.1.1 Edit the IDL file in order to fit the requirements.

1.2 Open a console/shell, navigate to the folder where you have

th

e idl file.1.3Write to the Console the command:IDLJ-fall Hello.idl

1.4 The result will be a bunch of java files which will beautomatically generated.

1.5 Th

e java files will be needed afterwards.


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application



3. Write the server application.4. Compile the two applications and start the server.

5. Run the client.


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Write the client application Notice: For running from Eclipse first

the command tnameserv ~/NS_Refmust be given in the console window ,

before starting the server.

In Unix machines you have to beadministrator and use the command

sudo tnameserv ORBInitialPortvalue to set the initial port.

javac Client_hello.java written in theconsole window will compile the javafile.

java Client_hello -ORBInitialHostnameserverhost-ORBInitialPortnameserverportto start the application

The fourth command can be usedwhen we want to set the port and hostwhich we want to use.

Default port for Unix andWindows is900.

public class Client_hello {

public static void main(String args[]) {String name_service = "Hello_server";

Properties properties = new Properties();properties.put("org.omg.CORBA.ORBInitialHost",localhost");properties.put( "org.omg.CORBA.ORBInitialPort",+ 900);

try {System.out.println("Client>Creating and initializing the ORB");ORB orb = ORB.init(args, null);System.out.println("Client>getting the root naming context");

org.omg.CORBA.Object objRef=orb.resolve_initial_references("NameService");// it uses NamingConetExt Interoperable Naming Service

NamingContextExt ncRef =NamingContextExtHelper.narrow(objRef);Resolving the object reference inNameComponent nc = new NameComponent(name_service,"");NameComponent path[] = { nc };Interface_Hello hello =Interface_HelloHelper.narrow(ncRef.resolve(path));calling the Hello service...");String msg_received = hello.get_msg();server returned the following message: "+ msg_received

}catch (Exception e) {System.out.println("Exception:\n" + e);


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application


2. Write the Client application.

3. Write the Server application.4. Compile the two applications and start the Server.

5. Run the Client.


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Notice: For running from Eclipse first the

command tnameserv ~/NS_Refmust begiven in the console window , beforestarting the server.

In Unix machines you have to beadministrator and use the command sudotnameserv ORBInitialPort value to setthe initial port.

javac Client_hello.java written in theconsole window will compile the javafile.

java Client_hello -ORBInitialHostnameserverhost-ORBInitialPortnameserverportto start the application

The fourth command can be used whenwe want to set the port and host which wewant to use.

Default port for Unix andWindows is900.

Write the server application

public class Server_hello {public static void main(String args[]) {

String name_service = "Hello_server";Properties properties = System.getProperties();try {

System.out.println("Server>starting server...");System.out.println("Server>creating and initializing the ORB");ORB orb = ORB.init(args, properties);System.out.println("Server>getting reference to rootpoa");......System.out.println("Server>activating the POA Manager");.......System.out.println("Server>Creating the servant");.......

Hello_service hello_service = new Hello_service();System.out.println("Server>obtain the reference from the servant");......

System.out.println("Server>getting the root naming context");org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService");NameComponent nc = new NameComponent(name_service, "");NameComponent path[] = { nc };ncRef.rebind(path, service_href);while (!msg_kbd.equals("quit") && !msg_kbd.equals("QUIT")) {msg_kbd= data_reader.readLine();if (msg_kbd.equals("quit") || msg_kbd.equals("QUIT")) {

}}

} catch (Exception e) {System.out.println("Exception in server...\nException:\n" + e);


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Steps needed for Creating and running a

application which uses CORBA



3. Write the server application.4. Compile the two applications and start the server.

5. Run the client.


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Get started with a basic CORBA application

4.Compile the two applications and start t

he Server

4.1 Start the Naming Server

4.2 Run the hello server.

5. Run the hello client and observe

the outputted message. The application

can run as a distributed application but

also as stand alone.


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Outline


Broker pattern short review


Conclusion


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Exercises

Task1: Learn how to use the IDLJ compiler. Download the Eclipse Application 1from the web site(5 minutes)

Easy. Generate Java Code from a IDL file supplied together with the project observe if thefiles match with the ones given.(15 minutes)

Medium. Implement your own hello service.

HomeworkTask2:Writing the required services for the server. Download the Idl file

Math.IDL and the two java files for the Client and Server .

Easy. Generate the java files from the idl files. Hard.Write a Service class used by the server where services like: addition, subtraction,

multiplication, transpose and quit(will stop the server) operations are implemented for basicmatrix operations


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Outline

Main Components of CORBA Architecture

Broker pattern short review


Conclusion


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Conclusions

Wide language support

Open Standard

Wide Platform Support

Usage of the Broker Pattern

Advantages of using the Broker Pattern

Others in File


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Questions


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References:

Books: CORBA Networking with Java, George M. Doss,Wordware Publishing INC CORBA 3 Fundamentals and Programming Sec Ed. John Siegel ,John Wilesy & Sons, INC.

CORBA A Guide to Common Object Request Broker Architecture, Ron Ben-Natan, McGraw-Hill

Links: CORBA EXPLAINED SIMPLY, Ciaran McHale http://www.ciaranmchale.com/corba-explained-simply/development-of-

corba-applications.html

CORBA Programming with J2SE 1.4 ,http://java.sun.com/developer/technicalArticles/releases/corba/

JavaTM IDL FAQ http://download.oracle.com/javase/1.3/docs/guide/idl/jidlFAQ.html#where%20can%20I%20download

A Short Guide To Learning CORBA,Michael Le and Jun Suzukihttp://netresearch.ics.uci.edu/bionet/resources/platform/corba/

What is CORBA? Tutorial ,http://www-cdfonline.fnal.gov/daq/CORBAXXX/tutorial.html

Introduction to CORBA ,By jGuru.com http://java.sun.com/developer/onlineTraining/corba/corba.html#co5

Catalog of OMG IDL / Language Mappings Specificationshttp://www.omg.org/technology/documents/idl2x_spec_catalog.htm#Java2IDL

Indroducing to IDL , by Jim Inscore,

http://www.csse.uwa.edu.au/programming/javatut/idl/index.html Java and CORBA - a smooth blend,by David Reilly

http://www.javacoffeebreak.com/articles/javaidl/javaidl.html#code

Einfhrung und Beschreibung der unterschiedlichen Client-Server Anwendungen mittels CORBA, basierend auf derProgrammiersprache Java, Cihan zkalfa,http://www.nt.fh-koeln.de/fachgebiete/inf/diplom/corba/html/kompilieren.html

IIOP: Internet Inter-ORB Protocol,http://panuganty.tripod.com/articles/iiop.htm

corba by paul m. pse 2010 better

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