This section contains:
![]() | The IDL for a simple "Hello World" program
![]() A transient server that creates an object and
registers it in a naming context
| ![]() An application client that, knowing
the object's name,
retrieves a reference for it from the naming context, and invokes
it
| ![]() An applet that does the same
| |
Instructions for compiling and running the example are provided, and source code is also included.
Note: The Hello World example is provided with
pre-built stub and skeleton files. However, to generate these files yourself
and take full advantage of this programming guide, you will need to
download the idltojava compiler.
Example IDL
The following example OMG IDL describes a CORBA object whose single sayHello() operation returns a string.
module HelloApp { interface Hello { string sayHello(); }; };
The example server consists of two classes, the servant and the server. The servant, HelloServant, is the implementation of the Hello IDL interface; each Hello instance is implemented by a HelloServant instance. The servant is a subclass of _HelloImplBase, which is generated by the idltojava compiler from the example IDL. The servant contains one method for each IDL operation, in this example, just the sayHello() method. Servant methods are just like ordinary Java methods; the extra code to deal with the ORB, with marshaling arguments and results, and so on, is provided by the server and the stubs.
The server class has the server's main() method, which:
![]() | Creates an ORB instance
![]() Creates a servant instance (the implementation of one CORBA
Hello object) and tells the ORB about it
| ![]() Gets a CORBA object reference for a naming context in which to
register the new CORBA object
| ![]() Registers the new object in the naming context under the name "Hello"
| ![]() Waits for invocations of the new object
| |
// Copyright and License import HelloApp.*; import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*; class HelloServant extends _HelloImplBase { public String sayHello() { return "\nHello world !!\n"; } } public class HelloServer { public static void main(String args[]) { try{ // create and initialize the ORB ORB orb = ORB.init(args, null); // create servant and register it with the ORB HelloServant HelloRef = new HelloServant(); orb.connect(HelloRef); // get the root naming context org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); NamingContext ncRef = NamingContextHelper.narrow(objRef); // bind the Object Reference in Naming NameComponent nc = new NameComponent("Hello", ""); NameComponent path[] = {nc}; ncRef.rebind(path, HelloRef); // wait for invocations from clients java.lang.Object sync = new java.lang.Object(); synchronized (sync) { sync.wait(); } } catch (Exception e) { System.err.println("ERROR: " + e); e.printStackTrace(System.out); } } }
The example application client that follows:
![]() | Creates an ORB
![]() Obtains a reference to the naming context
| ![]() Looks up "Hello" in the naming context and receives a reference to that CORBA object
| ![]() Invokes the object's sayHello() operation and prints
the result
| |
// Copyright and License import HelloApp.*; import org.omg.CosNaming.*; import org.omg.CORBA.*; public class HelloClient { public static void main(String args[]) { try{ // create and initialize the ORB ORB orb = ORB.init(args, null); // get the root naming context org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); NamingContext ncRef = NamingContextHelper.narrow(objRef); // resolve the Object Reference in Naming NameComponent nc = new NameComponent("Hello", ""); NameComponent path[] = {nc}; Hello HelloRef = HelloHelper.narrow(ncRef.resolve(path)); // 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); } } }
The example applet client that follows:
![]() | Creates an ORB
![]() Obtains a reference to the naming context
| ![]() Looks up "Hello" in the naming context and receives a reference to that CORBA object
| ![]() Invokes the object's sayHello() operation and prints
the result
| |
// Copyright and License import HelloApp.*; import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*; import java.awt.Graphics; public class HelloApplet extends java.applet.Applet { public void init() { try { // create and initialize the ORB ORB orb = ORB.init(this, null); // get the root naming context org.omg.CORBA.Object objRef = orb.resolve_initial_references("NameService"); NamingContext ncRef = NamingContextHelper.narrow(objRef); // resolve the Object Reference in Naming NameComponent nc = new NameComponent("Hello", ""); NameComponent path[] = {nc}; Hello HelloRef = HelloHelper.narrow(ncRef.resolve(path)); // call the Hello server object and print results message = HelloRef.sayHello(); } catch (Exception e) { System.out.println("HelloApplet exception: " + e.getMessage()); e.printStackTrace(System.out); } } public void paint(Graphics g) { g.drawString(message, 25, 50); } String message = ""; }
The source code for the Hello World example is located in the examples/hello directory. The following instructions assume you can use port 1050 for the Java IDL name server. Substitute a different port if necessary. Note that for ports below 1024, you need root access on UNIX machines, and administrator privileges on Windows95 and NT. Note also that the instructions use a slash (/) for path names. Windows95 and NT users should subtitute a backslash (\).
Note: The Hello World example is provided with pre-built stub and skeleton files. However, to generate these files yourself, you will need to download the idltojava compiler.
![]() | Change to the directory that contains the file Hello.idl
cd docs/guide/idl/examples/hello ![]() Run idltojava on the IDL file to
create stubs and skeletons:
| idltojava Hello.idl ![]() Compile the .java files, including the stubs and skeletons:
| javac *.java HelloApp/*.java ![]() Make sure the name server is running:
| tnameserv -ORBInitialPort 1050& ![]() Start the Hello server:
| java HelloServer -ORBInitialPort 1050 ![]() Run the Hello application client from a different shell than the
server:
| java HelloClient -ORBInitialPort 1050 |
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