CORBA Barış COŞKUN Çağatay DİKİCİ

INTRODUCTION Computer networks are heterogenous In 1989 OMG(Object Management Group) was formed to address the problems of developping portable distributed applications for heteregenous systems OMG supplies CORBA specifications

CORBA BASICS CORBA (Common Object Request Broker Architecture) Provides platform independent program interfaces and models for portable distributed object oriented computer applications

CORBA Brings... Partial failures Impact of latency Load Balancing Language Independency

CORBA concepts Corba Object Client Server Object Reference Servant

CORBA requirements IDL (Interface Definition Language) ORB (Object Request Broker) POA (Portable Object Adapter)

IDL Both server and client should know the general specification of the CORBA object. IDL defines language bindings for many different programming languages.(C,C++,Java,COBOL...) Stub and Skeleton are generated from IDL

ORB Locates the remote object on the network Transports the request to the object Waits for results and transports results from object to client Implements location transparency

IIOP

POA Manages server-side resources by set of policies – LifeSpan Policy Transient Persistent – Servant Retention Policy Retain Non-Retain

How can ORB locate Objects? Naming Service (Tnameserv.exe) – ServerSide Bind (host,port,object,name) – ClientSide Lookup(host,port,name)  get (object)

CORBA Interface Definition Language (IDL) OMG IDL is an object-oriented interface definition language that used to specify interfaces containing methods and attributes Support interface inheritance OMG IDL is designed to map onto multiple programming language

OMG IDL Compiler A OMG IDL compiler generates client stubs and server skeletons OMG IDL supports the following features: *modules *interfaces *methods *attributes *inheritance *arrays *exceptions

OMG IDL vs C++ No data members No pointers No constructors or destructors No overloaded methods No int data type String type

The Hello Client Server Example

Example (cont..) Writing the IDL Interface Developing the Hello World Server Developing a Client Application Compiling and Running the Application

Writing IDL Interface(Hello.idl) module HelloApp { interface Hello { string sayHello(); };

Writing the Remote Object Implementation Public class HelloServant extends _HelloImplBase { public String sayHello() { return "\nHello world!!\n"; }

Writing Object Server Overview Initialize the ORB Create an instance of the remote object Connect the remote object to the ORB Assign the remote object a name in the CORBA Name Service

HelloServer.java import HelloApp.*; import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*; public class HelloServer { public static void main(String args[]) { try{ ORB orb = ORB.init(args, null); HelloServant helloRef = new HelloServant(); orb.connect(helloRef);

org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); NamingContext ncRef = NamingContextHelper.narrow(objRef); NameComponent nc = new NameComponent("Hello", ""); NameComponent path[] = {nc}; ncRef.rebind(path, helloRef); java.lang.Object sync = new java.lang.Object(); synchronized(sync){ sync.wait(); } } catch(Exception e) { System.err.println("ERROR: " + e); e.printStackTrace(System.out); } }}

Client Development Overview Initialize the ORB and Naming Service Look up the object in the Naming Service Call Remote Methods

HelloClient.java import HelloApp.*; import org.omg.CosNaming.*; import org.omg.CORBA.*; public class HelloClient { public static void main(String args[]) { try{ ORB orb = ORB.init(args, null); org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); NamingContext ncRef = NamingContextHelper.narrow(objRef);

NameComponent nc = new NameComponent("Hello", ""); NameComponent path[] = {nc}; Hello helloRef = HelloHelper.narrow(ncRef.resolve(path)); String hello = helloRef.sayHello(); System.out.println(hello); } catch(Exception e) { System.out.println("ERROR : " + e); e.printStackTrace(System.out); } } }

Compiling and Running the Application Compile Client and Server javac HelloClient.java HelloServer.java Running the Application tnameserv (default port 900) java HelloServer –ORBInitialHost java HelloClient –ORBInitialHost