Slide 1 Objektorienteret Middleware (OOMI) CORBA Programming: Presentation of a simple “Hello World” CORBA client and server application

Slide 2 Outline CORBA programming Code examples We will make a very small CORBA application with a Java server, Java Client & C++ client application In Java (SUN ORB) What gets generated? What files do we need to write (client + server)? In Orbacus C++ ORB We make a client Only small steps in CORBA programming – much complexity

Slide 3 “Hello World” CORBA Example with file IOR Client app. Server app. Development PC CORBA Java / C++ Hello World Client CORBA Java Hello World Server TCP/IP Network TCP/IP Network User activa- tes client Server returns “Hello World !“

Slide 4 Who’s doing what? Some code will get generated by the IDL compiler Some code we will need to implement ourselves Starting with the IDL file

Slide 5 IDL Interface of Hello Servant module HelloApp interface Hello { string sayHello(); };

Slide 6 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 7 Extract from _HelloStub.java What are we looking at?

Slide 8 Extract from HelloHelper.java Discuss with your neighbor 2 min. what is this? what is it used for?

Slide 9 Extract from HelloPOA Discuss with your neighbor 2 min. what is this? what is used for? More on this later

Slide 10 // 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 11 //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 Implemented manually

Slide 12 // 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 Discuss with your neighbor 2 min. what happens after sayHello()

Slide 13 What is this object.ref file? IOR: Interoperable Object Reference Includes info on: Repository ID (standard), Endpoint Info (standard) - including IP and port number, Object Key (proprietary) Can be written into a file Not really nice with a file-based reference – or what? May employ a naming service instead This we shall look at later File-based may be necessary due to firewall problems Possible to use a HTTP or FTP server for distributing the references IOR: c3 a48656c6c6f f48656c6c6 f3a312e c e e e312e b afabcb a80a a

Slide 14 Parsed IOR _IIOP_ParseCDR: byte order BigEndian, repository id, 1 profile _IIOP_ParseCDR: profile 1 is 138 bytes, tag 0 (INTERNET), BigEndian byte order (iiop.c:parse_IIOP_Profile): bo=BigEndian, version=1.2, hostname= , port=1658, object_key= (iiop.c:parse_IIOP_Profile): encoded object key is (iiop.c:parse_IIOP_Profile): non-native cinfo is object key is ; no trustworthy most-specific-type info; unrecognized ORB type; reachable with IIOP 1.2 at host " ", port For the translation of IORs

Slide 15 #include int run(CORBA::ORB_ptr); int main(int argc, char* argv[]) {int status = EXIT_SUCCESS; CORBA::ORB_var orb; try { orb = CORBA::ORB_init(argc, argv); status = run(orb); } catch (const CORBA::Exception&) { status = EXIT_FAILURE; } if(!CORBA::is_nil(orb)) { try { orb -> destroy(); } catch(const CORBA::Exception&) {status = EXIT_FAILURE; } } return status; } HelloCorba C++ Client Part 1 Init ORB Destroy ORB Call run method (see next slide) Implemented manually

Slide 16 … int run(CORBA::ORB_ptr orb) { const char* refFile = "object.ref"; ifstream in(refFile); char s[2048]; in >> s; CORBA::Object_var obj = orb -> string_to_object(s); HelloApp::Hello_var hello = HelloApp::Hello::_narrow(obj); cout sayHello() << endl; return 0; } HelloCorba C++ Client Part 2 Narrow the call (CORBA type cast) to the Hello_var smartpointer (helper + memory management) Narrow the call (CORBA type cast) to the Hello_var smartpointer (helper + memory management) Object reference Read from file Object reference Read from file Call method via Proxy and print result HelloApp::Hello_var smartpointer type Generated by IDL compiler + Hello Read more on Smartpointer types in OOMI-1 chapter 4

Slide 17 Læringsmål Alignment Når kurset er færdigt forventes den studerende at kunne: Definere, beskrive og sammenligne forskellige typer af objektorienterede middleware frameworks til apparater og computere, med primær fokus på CORBA og sekundært ICE teknologierne, herunder fordele og ulemper forbundet med de forskellige teknologier Definere og beskrive principper omkring transparens og heterogenitet i relation til middlewareteknologier Definere og beskrive gængse teorier, metoder og retningslinier indenfor det objektorienterede middleware paradigme og anvende disse til at designe effektive distribuerede systemer Designe og konstruere et distribueret system der gør brug af CORBA og ICE teknologierne med tilhørende værktøjssupport I kan nu definere og beskrive Grundlæggende CORBA kodearkitektur og kode I kan nu definere og beskrive Grundlæggende CORBA kodearkitektur og kode Kode til stubbe, proxy, IDL, Retningslinier, transp., hetero. IDL Compiler, referencer Kode til stubbe, proxy, IDL, Retningslinier, transp., hetero. IDL Compiler, referencer Grundlæggende forståelse For hvad der skal til af Java og C++ Kode til et CORBA system Grundlæggende forståelse For hvad der skal til af Java og C++ Kode til et CORBA system MANGLER: praktisk erfaring: kommer med øvelser og opgave