Slide 1 Objektorienteret Netværkskommunikation CORBA Introduction

Slide 2 Outline CORBA Introduction & Background Architecture Session & Presentation layer GIOP / IIOP / CDR CORBA Interface Definition Language – IDL Language mappings CORBA development steps Code Examples in Java / C++ Alignment

Slide 3 Who is the OMG? OMG: Object Management Group Non-profit organization in the US Founded April 1989 More than 800 members Dedicated to creating and popularizing object-oriented industry standards for application integration, e.g. CORBA 1.0 (1995) –> CORBA (2006) UML 1.1 nov > 2.1 (2006)

Slide 4 Goal of CORBA CORBA: Common Object Request Broker Architecture Support distributed and heterogeneous object request in a way transparent to users and application programmers Facilitate the integration of new components with legacy components Open standard that can be used free of charge Based on wide industry consensus But not much Microsoft support Problem with CORBA Considered too complex by many

Slide 5 The Specifications CORBA is a collection of specifications og.htmhttp:// og.htm Common Object Request Broker Architecture (CORBA/IIOP) (3.0.3) CORBA Component Model (CCM) (3.0) Light Weight CCM CORBA/e (replaces Minimum CORBA) Minimum CORBA (1.0) Real-Time CORBA (Dynamic Scheduling) (2.0) Real-Time CORBA (Static Scheduling) (1.1) Others

Slide 6 Families of specifications: CORBAservices Specifications CORBAfacilities Specifications OMG Domain Specifications IDL / Language Mapping Specifications Many others Realted to UML UML Profile for CORBA (1.0)

Slide 7 Application Objects CORBA Facilities CORBA Services (mandatory) Domain Interfaces Object Management Architecture (OMA) Object Request Broker

Slide 8 CORBA Architecture1 Many different vendors and ORB types Many of which do not interoperate Must check specification OrbBacus from IONA produces both C++ and Java Sun J2SE SDK has only Java-based ORB C++ ORB from IONA will work with SUN ORB as specified Many others MicoORB, Middcor, TAO, openORB, VisiBroker

Slide 9 One standardised interface One interface per object operation ORB-dependent interface One interface per object adapter Dynamic Invocation Client Stubs ORB Interface Implementation Skeletons Client Object Implementation ORB Core Object Adapter CORBA Architecture 2

Slide 10 CORBA 2.0 Applications GIOP ESIOP IIOPDOETalk DCE-CIOP Mandatory: provides "out of the box" interoperability Interoperability Protocols Environment Specific.. IIOP: Internet Inter-ORB Protocol is the primary CORBA transport protocol

Slide 11 General Inter-ORB Protocol GIOP: Handles the session & presentation layer Defines seven message primitives: Request, Reply, Locate Request, Locate Reply, Cancel request, Close Connection, Message Error Binary formatted More simple than JRMP for Java RMI Internet Inter-ORB Protocol (IIOP) Maps GIOP to TCP/IP Provides operations to open and close TCP/IP connections Is required from ORBs for CORBA compliance But intra vendor ORB com is not restricted to this More on the IIOP in TIOOMI if wanted

Slide 12 Common Data Representation (CDR) Defined as part of GIOP Presentation layer implementation to support heterogeneity Mapping of IDL data types to transport byte stream Encodings of primitive types constructed types interoperable object references

Slide 13 Recap - motivation for an IDL IDL: Interface Definition Language Components of distributed systems are written in different programming languages Programming languages may or may not have their own object model Object models largely vary Differences need to be overcome in order to facilitate integration

Slide 14 Heterogeneous OO Network CORBA C++ Client App.3 CORBA C# Client App.2 CORBA Java Client App.1 TCP/IP Network CORBA Cobol Database Server DB “Object Wrapping of non OO application” Different ORB’s from different vendors, on different operating systems – and written in different languages = Heterogenity

Slide 15 PL IDL CORBA IDL & Mappings Avoid multiple mappings

Slide 16 IDL Common Object Model Smalltalk Cobol Java Ada-95 C++ C C CORBA Programming Language Bindings.NET Janeva / Middcor (C#) /.NET REMoting

Slide 17 Interface Definition Language Akronym: IDL Language for expressing all concepts of the middleware’s object model Should be programming-language independent not computationally complete Bindings to different programming languages are needed language bindings are specified by CORBA

Slide 18 CORBA Object Model: Subtypes interface Organization { readonly attribute string name; }; interface Club : Organization { exception NotInClub{}; readonly attribute short noOfMembers; readonly attribute Address location; attribute TeamList teams; attribute TrainerList trainers; void transfer(in Player p) raises NotInClub; }; Inherited by Club Supertype Implicit supertype: Object This has only been a minimal presentation of the IDL

Slide 19 Interface Definition Design Server Stub Generation Client Stub Generation Server Coding Client Coding Server Registration Development Steps – CORBA vs RMI & SOAP SOAP: WSDL Java2WSDL WSDL2JAVA AXIS SOAP RMI: rmic RMI: JAVA J2SE JDK Start with Server Interface Coding: JAVA Start with Server Interface Coding: JAVA rmiregistry CORBA CORBA: IDL ORB RMI: JAVA interface C++, Java …

Slide 20 C++ Compiler, Linker Server Client.cc Server.cc C++ Compiler, Linker Client Team.idl included in generates reads IDL-Compiler Teamcl.hh Teamcl.cc Teamsv.cc Teamsv.hh CORBA Client and Server Implementation Next we will look into a simple CORBA programming example

Slide 21 IDL Interface of Hello Servant module HelloApp interface Hello { string sayHello(); };

Slide 22 IDL Compiler Example Java Hello.idl file Java IDL Compiler - IDLJ Hello.java (Both Client & Server) contains the Java version of the IDL interface. HelloOperations.java contains the methods – here only sayHello(). All the operations in the IDL interface are placed in the operations file. _HelloStub.java is the client stub. HelloPOA.java is the skeleton class you should extend from. It implements dynamic invocation functions. HelloHelper.java (Both Client & Server) provides auxiliary functionality, notably the narrow() method required to cast CORBA object references to their proper types. HelloHolder.java Whenever the IDL type is an out or an inout parameter, the Holder class is used. Generates Input What gets generated by the IDL Compiler

Slide 23 Extract from _HelloStub.java What are we looking at?

Slide 24 Extract from HelloHelper.java

Slide 25 Extract from HelloPOA

Slide 26 // HelloServer.java, stringified object reference version // Stefan Wagner, 2003 import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*; import org.omg.PortableServer.*; import org.omg.PortableServer.POA; import HelloApp.*; //This is the servant - implementing the methods from the IDL class HelloServant extends HelloPOA { private ORB orb; public HelloServant(ORB orb) { this.orb = orb; } public String sayHello() { return "\nHello world !!\n"; } Constructor taking ORB as a parameter (from HelloPOA) HelloServant The server object (Part 1) The CORBA operation implemented By extending from HelloPOA we may communicate with ORB Implemented manually

Slide 27 //This is the HelloServer - the server running the HelloServant - Servant public class HelloServer { public static void main(String args[]) { try{ // create and initialize the ORB org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, null); // create servant and register it with the ORB HelloServant helloRef = new HelloServant(orb); // get reference to rootpoa and activate the POAManager POA rootpoa = POAHelper.narrow(orb.resolve_initial_references("RootPOA")); rootpoa.the_POAManager().activate(); // get object reference from the servant org.omg.CORBA.Object ref = rootpoa.servant_to_reference(helloRef); Hello href = HelloHelper.narrow(ref); // stringify the helloRef and dump it in a file String oir = orb.object_to_string(href); java.io.PrintWriter out = new java.io.PrintWriter(new java.io.FileOutputStream("object.ref")); out.println(oir); out.close(); // wait for invocations from clients orb.run(); } catch (Exception e) { System.err.println("ERROR: " + e); e.printStackTrace(System.out); } } } HelloServant The server object (Part 2) Init ORB and register servant with ORB Start the orb server process The POA produces the reference Narrow the call (CORBA type cast + IDL type check) Object reference ”stringified” and Sent to file object.ref Object reference ”stringified” and Sent to file object.ref Activate rootPOA

Slide 28 // HelloClientSOR.java, stringified object reference version import java.io.*; import org.omg.CORBA.*; import HelloApp.HelloHelper; import HelloApp.*; public class HelloClientSOR { public static void main(String args[]) { try { // create and initialize the ORB org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, null); // Get the stringified object reference and destringify it. java.io.BufferedReader in = new java.io.BufferedReader(new java.io.FileReader("object.ref")); String ref = in.readLine(); org.omg.CORBA.Object obj = orb.string_to_object(ref) ; Hello helloRef = HelloHelper.narrow(obj); // call the Hello server object and print results String Hello = helloRef.sayHello(); System.out.println(Hello); } catch (Exception e) { System.out.println("ERROR : " + e) ; e.printStackTrace(System.out);} } HelloClientSOR The Client program Init ORB Narrow the call (CORBA type cast + IDL type check) Object reference Read from file Object reference Read from file Call via Proxy Implemented manually