CORBA Programming: Presentation of a simple “Hello World” CORBA client and server application

Only small steps in CORBA programming – much complexity 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

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

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

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

IDL Compiler Example Java 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. Hello.idl file Java IDL Compiler -IDLJ Generates Input What gets generated by the IDL Compiler

Extract from _HelloStub.java What are we looking at?

Extract from HelloHelper.java Discuss with your neighbor 1 min. what is this? what is it used for?

Discuss with your neighbor 1 min. what is this? what is used for? Extract from HelloPOA More on this later Discuss with your neighbor 1 min. what is this? what is used for?

HelloServant The server object (Part 1) Implemented manually // 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"; HelloServant The server object (Part 1) Implemented manually By extending from HelloPOA we may communicate with ORB Constructor taking ORB as a parameter (from HelloPOA) The CORBA operation implemented

HelloServant The server object (Part 2) //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 Activate rootPOA The POA produces the reference Narrow the call (CORBA type cast + IDL type check) Object reference ”stringified” and Sent to file object.ref Start the orb server process

Narrow the call (CORBA type cast + IDL type check) // 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 Implemented manually Init ORB Object reference Read from file Narrow the call (CORBA type cast + IDL type check) Call via Proxy

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:000000000000001749444c3a48656c6c6f4170702f48656c6c6f3a312e30000000000001000000000000006c000102000000000e3139322e3136382e312e3130300011b600000021afabcb0000000020a80a250300000001000000000000000000000004000000000a0000000000000100000001000000200000000000010001000000020501000100010020000101090000000100010100

Call run method (see next slide) #include <OB/CORBA.h> #include <Hello.h> #include <fstream.h> 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 Implemented manually Init ORB Call run method (see next slide) Destroy ORB

HelloCorba C++ Client Part 2 … 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 << hello->sayHello() << endl; return 0; } HelloCorba C++ Client Part 2 Object reference Read from file HelloApp::Hello_var smartpointer type Generated by IDL compiler + Hello Narrow the call (CORBA type cast) to the Hello_var smartpointer (helper + memory management) Call method via Proxy and print result Read more on Smartpointer types in OOMI-1 chapter 4