Slide 1 of 15 © Ingeniørhøjskolen i Århus CORBA Programming: Presentation of a simple “Hello World” CORBA client and server application

Slide 2 of 15 © Ingeniørhøjskolen i Århus 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

Slide 3 of 15 © Ingeniørhøjskolen i Århus “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 Networ k TCP/IP Networ k User activa- tes client Server returns “Hello World !“

Slide 4 of 15 © Ingeniørhøjskolen i Århus Who’s doing what? Some code will get generated by the IDL compiler Some code we will need to implement ourselves Staring with the IDL file

Slide 5 of 15 © Ingeniørhøjskolen i Århus IDL Interface of Hello Servant module HelloApp interface Hello { string sayHello(); };

Slide 6 of 15 © Ingeniørhøjskolen i Århus 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 of 15 © Ingeniørhøjskolen i Århus Extract from _HelloStub.java

Slide 8 of 15 © Ingeniørhøjskolen i Århus Extract from HelloHelper.java

Slide 9 of 15 © Ingeniørhøjskolen i Århus Extract from HelloPOA

Slide 10 of 15 © Ingeniørhøjskolen i Århus // 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

Slide 11 of 15 © Ingeniørhøjskolen i Århus //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 12 of 15 © Ingeniørhøjskolen i Århus // 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

Slide 13 of 15 © Ingeniørhøjskolen i Århus 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 of 15 © Ingeniørhøjskolen i Århus #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)

Slide 15 of 15 © Ingeniørhøjskolen i Århus … 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