CORBA Chapter 17 Coulouris text

Today’s Topics CORBA History and goals CORBA RMI CORBA services The Distributed Whiteboard Revisited

CORBA History and Goals Object Management Group Formed in 1989 Goals: -- OOP on distributed systems -- heterogeneous hardware -- heterogeneous OS -- different programming languages

History and Goals OMG Introduced the Object Request Broker (ORB) The role of the ORB is to help a client find an object, activate the object if necessary, and call a method on the object. Common Object Request Broker Architecture (CORBA) agreed to by a group of companies in 1991 CORBA 2.0 specification released in 1996

History and Goals CORBA 2.0 specification defined standards for different implementations of CORBA to communicate with one another These standards are called the General Inter-ORB protocol (GIOP) and may run over various transports GIOP over TCP/IP is called the Internet Inter-ORB Protocol

CORBA RMI Main components -- An Interface Definition language (IDL) that promotes the use of different programming languages, stubs are generated in the client’s language and skeletons are generated in the server’s language -- An architecture -- GIOP defines an external data representation (CDR) as well as message formats and message types -- Message types include request and reply as well as location requests, errors, and request cancellations

CORBA Services A set of generic services that can be used for distributed application -- Naming Service (location by name) -- Trading Service (location by attribute - directory service) -- Event Service -- Security Service (authentication, ACL’s, auditing, non- repudiation) -- Transaction Service (begin, commit, rollback a series of RMI calls ) -- Persistent Object Service (POS)

The Distributed Whiteboard Example in CORBA

IDL interfaces Shape and ShapeList struct Rectangle{ // no class in IDL 1 long width; long height; long x; long y; } ; struct GraphicalObject {2 string type; Rectangle enclosing; boolean isFilled; }; interface Shape {3 long getVersion() ; GraphicalObject getAllState() ; // returns state of the GraphicalObject }; typedef sequence All; // All is a 100 element array4 interface ShapeList {5 exception FullException{ }; 6 Shape newShape(in GraphicalObject g) raises (FullException);7 All allShapes(); // returns sequence of remote object references8 long getVersion() ; // parameters are in, out, or both }; // parameters may be primitive, struct or array and // are passed by value // parameters whose type is an IDL interface // is passed by remote reference

idltojava Run idltojava on the above interface The command idlj is found in j2sdk1.4.2\bin The Java 2 Platform, Standard Edition, v1.4, provides an Object Request Broker (ORB) runtime component The JDK documentation states that its Java ORB has not been tested with ORB’s written in other languages JDK 1.4 provides an Orb class with a pluggable architecture

From the JDK Doc OMG specifies a mapping from IDL to several different programming languages, including Java, C, C++, Lisp, Python, Smalltalk, COBOL, and Ada. When mapped, each statement in OMG IDL is translated to a corresponding statement in the programming language of choice.

Java interface ShapeList generated by idltojava from CORBA interface ShapeList public interface ShapeList extends org.omg.CORBA.Object { Shape newShape(GraphicalObject g) throws ShapeListPackage.FullException; Shape[] allShapes(); int getVersion(); }

S hapeListServant class from CORBA interface ShapeList import org.omg.CORBA.*; class ShapeListServant extends _ShapeListImplBase { ORB theOrb; private Shape theList[]; private int version; private static int n=0; public ShapeListServant(ORB orb){ theOrb = orb; // initialize the other instance variables } public Shape newShape(GraphicalObject g) throws ShapeListPackage.FullException {1 version++; Shape s = new ShapeServant( g, version); if(n >=100) throw new ShapeListPackage.FullException(); theList[n++] = s;2 theOrb.connect(s); return s; } public Shape[] allShapes(){... } public int getVersion() {... } }

Java class ShapeListServer import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*; public class ShapeListServer { public static void main(String args[]) { try{ ORB orb = ORB.init(args, null);1 ShapeListServant shapeRef = new ShapeListServant(orb);2 orb.connect(shapeRef);3 org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); 4 NamingContext ncRef = NamingContextHelper.narrow(objRef); NameComponent nc = new NameComponent("ShapeList", "");5 NameComponent path[] = {nc};6 ncRef.rebind(path, shapeRef); 7 java.lang.Object sync = new java.lang.Object(); synchronized (sync) { sync.wait();} } catch (Exception e) {... } }

Java client program for CORBA interfaces Shape and ShapeList import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*; public class ShapeListClient{ public static void main(String args[]) { try{ ORB orb = ORB.init(args, null); 1 org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); NamingContext ncRef = NamingContextHelper.narrow(objRef); NameComponent nc = new NameComponent("ShapeList", ""); NameComponent path [] = { nc }; ShapeList shapeListRef = ShapeListHelper.narrow(ncRef.resolve(path)); 2 Shape[] sList = shapeListRef.allShapes(); 3 GraphicalObject g = sList[0].getAllState(); 4 } catch(org.omg.CORBA.SystemException e) {...} }

The main components of the CORBA architecture client server proxy or dynamic invocation implementation repository object adapter ORB skeleton or dynamic skeleton client program interface repository Request Reply core for A Servant A

Naming graph in CORBA Naming Service initial naming context ShapeList C DE B initial naming context P R S T V Q U XX

Where are we heading? Working with J2EE using JBoss Integrating web services with J2EE

SOAP and J2EE Slide from JAXM/JMS tutorial at Sun Microsystems