Getting Started: Hello World

Introductory information about the tutorial (in this file) includes:

Hello World Program Overview
Tutorial Overview
Previewing Hello World
For More Information

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 Tutorial, you will need to download the idltojava compiler.

Hello World Program Overview

This tutorial teaches the basic tasks in building a CORBA distributed application using Java IDL. You will build the classic "Hello World" program as a distributed application, with both applet and application clients.The Hello World program has a single operation that returns a string to be printed. Its basic function is illustrated below:

Operation of the Distributed Hello World Program

The client (applet or application) invokes the sayHello() operation of the HelloServer.
The ORB transfers that invocation to the servant object registered for that IDL interface.
The servant's sayHello() method runs, returning a Java String.
The ORB transfers that String back to the client.
The client prints the value of the String.

Tutorial Overview

Despite its simple design, the Hello World program lets you learn and experiment with all the tasks required to develop almost any CORBA program that uses static invocation.

Each lesson has a directory in the docs/guide/idl/tutorial directory of your JDK installation containing valid source files and compiled class files needed for completing the lesson. Although the lessons are designed to build upon one another, you can do the lessons in any order you want by using the files provided.

The lessons in this tutorial are listed below.

Lesson 1: Writing the IDL Interface teaches:
- How to write a simple IDL interface definition
- How to translate the IDL interface to Java
- The purpose of each file generated by the idltojava compiler
Lesson 2: Developing a Client Application teaches how to write a simple client application, including:
- How to create an ORB object
- How to use the naming service to get an initial object reference
- How to invoke an operation on a CORBA object
Lesson 3: Developing a Client Applet teaches how to write a client applet that performs the same functions as the client application.
Lesson 4: Developing the Hello World Server teaches how to write a simple server, including:
- How to create an ORB object for the server
- How to instantiate the servant and connect it to the ORB
- How to register the servant with the naming service
- How to make the server wait for invocations on the servant
Lesson 5: Using Stringified Object References teaches how to make an object reference when there is no naming service.

Previewing Hello World

You can run the Hello World application before you work through the tutorial. Follow the instructions listed for your operating system:

Building Hello World under the Solaris^TM Operating System
Building Hello World under the Windows Operating System

Building Hello World under the Solaris Operating System

The source code for the Hello World example is located in [Path_to_JDK]/docs/guide/idl/examples/Hello. The following instructions assume you can use port 1050 for the Java IDL name server. Substitute a different port if necessary. (Note that to use a port below 1024, you need root access on Unix machines and administrator privileges on Wintel machines.) Substitute the completely-qualified path to your JDK installation for [Path_to_JDK]

Note: Steps 2 and 3 require you to have downloaded and installed the idltojava compiler.

Change to the example directory:

cd [Path_to_JDK]/docs/guide/examples/hello

Make certain that the idltojava compiler [Path_to_JDK]/bin) and the Java binaries are included in your path environment variable.
Compile the IDL file with idltojava to create stubs and skeletons.
Note: idltojava is hard-coded to use a default preprocessor. On Solaris machines, it uses the path /usr/ccs/lib/cpp when looking for the preprocessor. You can change the preprocessor that idltojava uses by setting two environment variables: CPP and CPARGS. Set CPP to the full pathname of the preprocessor you want to use. Set CPARGS to the complete list of arguments to be passed to the preprocessor. You can also turn off the preprocessor by adding -fno-cpp to the idltojava command line. More information is available in the idltojava reference page that is downloaded with the idltojava compiler.
```
idltojava Hello.idl
```
Compile the Java files, including the stubs and skeletons:
```
javac *.java HelloApp/*.java
```

Start the Java IDL name server:

tnameserv -ORBInitialPort 1050 &

You will see something like the following:

Initial Naming Context:
IOR:000000000000002849444c3a6f6d672e6f72672f436f734e616d696e672f4e616d696e67436f6e746578743a312e3000000000010000000000000034000100000000000974687572626c6967000086760000001cafabcafe0000000233de2f5c00000000000000080000000000000000
TransientNameServer: setting port for initial object references to: 1050

The server runs in the background; you see no more evidence of it until you run the client program.

Start the Hello server:
```
java HelloServer -ORBInitialPort 1050 &
```
Run the Hello application client:
```
java HelloClient  -ORBInitialPort 1050
```
The string prints to the command line:
```
Hello world!!
```

The name server and the Hello World server, like many CORBA servers, run until you explicitly stop them. To avoid having many servers running, kill the server processes before proceeding to Lesson One.

Building Hello World under the Windows Operating System

Using Windows 95 or Windows NT, the source code for the Hello World example is located in [Path_to_JDK]\docs\guide\idl\examples\Hello. The following instructions assume you can use port 1050 for the Java IDL name server. Substitute a different port if necessary. Substitute the completely-qualified path to your JDK installation for [Path_to_JDK]

Note: Steps 2 and 3 require you to have downloaded and installed the idltojava compiler.

Change to the example directory:

cd [Path_to_JDK]\docs\guide\idl\examples\hello

Make certain that the idltojava compiler ([Path_to_JDK]\bin) and the Java binaries are included in your path environment variable.
Translate the IDL file to Java with the idltojava compiler to create stubs and skeletons.
Note: idltojava is hard-coded to use a default preprocessor. On Windows machines, it uses the MS Visual C++ preprocessor. You can change the preprocessor that idltojava uses by setting two environment variables: CPP and CPARGS. Set CPP to the full pathname of the preprocessor you want to use. Set CPARGS to the complete list of arguments to be passed to the preprocessor. You can also turn off the preprocessor by adding -fno-cpp to the idltojava command line. More information is available in the idltojava reference page that is downloaded with the idltojava compiler.
```
idltojava Hello.idl
```
Compile the Java files, including the stubs and skeletons:
```
javac *.java HelloApp\*.java
```
Start the Java IDL name server:
```
tnameserv -ORBInitialPort 1050
```
The server runs in the background; you see no more evidence of it until you run the client program.
Start the Hello server:
```
java HelloServer -ORBInitialPort 1050
```
Run the Hello application client:
```
java HelloClient -ORBInitialPort 1050
```
The string prints to the command line:
```
Hello world!!
```

For More Information

Although concepts are explained as they are introduced in the tutorial, you will find a discussion in greater depth and useful background information in the Fundamentals section. In addition, new terms are linked to their definitions throughout the tutorial.

Also, CORBA for Beginnners from the Object Management Group provides another source of basic CORBA information.

Lesson One

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