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<title>Exposing CORBA Services as Web Services</title>
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<h1>Exposing CORBA Services as Web Services</h1>

<h2>Overview</h2>
<h3>What is CORBA?</h3>
CORBA stands for Common Object Request Broker Architecture. It allows clients to invoke methods of remote objects running on remote machines through a binary protocol such as IIOP.

<h3>What Axis2 CORBA module does?</h3>

The Axis2 CORBA module acts as a bridge between SOAP and IIOP protocols by converting SOAP messages originated from a web services client to IIOP messages and vise versa. In other words, Axis2 CORBA module allows web service client to invoke methods on a remote CORBA server.
<h4>Features</h4>
<ul>
<li>Supports all the primitive and composite IDL data types including Value types (objects by value), Structures, Union, Sequences and Arrays (including multidimensional arrays), Enumerations and Exceptions.</li>
<li>Dynamic conversion of complex data types</li>
<li>IDL driven WSDL generation</li>
<li>Supports CORBA pre-processor directives</li>
</ul>

<h3>Why it is Useful?</h3>
<ul>
<li>Convert legacy CORBA services into web services</li>
<li>Facilitate interoperability between heterogeneous systems</li>
<li>Integrate CORBA services with Enterprise Service Buses (ESBs)</li>
</ul>


<h2>Tutorial</h2>

This tutorial explains how to write a simple CORBA service and how to make it available as a web service using the Axis2 CORBA module. Let's start the tutorial by creating an IDL file.

<h3>Prerequisites</h3>
<ul>
<li>Sun JDK version 5.0 or higher</li>
<li>Latest version of Axis2 with Axis2 CORBA module</li>
</ul>

<h3>Creating the IDL file</h3>
The Interface Definition Language (IDL) is used to describe the interface to a CORBA object. An IDL file can then be used to generate the source code for the CORBA server.

Copy the following listing and save as a text file named <tt>calculator.idl</tt>.

<pre>
// Address book system module
module example
{
    // A data structure which contains two integer values
    struct numbers
    {
        long first;
        long second;
    };
 
    // Specify interface to our address book
    interface calculator
    {
        // returns n.first + n.second
        long add(in numbers n);

        // returns n.first + n.second
        long subtract(in numbers n);
    };
};
</pre>

<h3>Creating the CORBA server</h3>
Open a console window and type the following command. (Make sure JAVA_HOME/bin is included to the PATH environment variable)

<pre>idlj -fall calculator.idl</pre>

idlj generates several classes needed for CORBA servers and client. Typically, idlj command will generate the following file structure.

<pre>
|
|   calculator.idl
|
\---example
        numbersHelper.java
        numbersHolder.java
        numbers.java
        calculatorPOA.java
        _calculatorStub.java
        calculatorHolder.java
        calculatorHelper.java
        calculator.java
        calculatorOperations.java
</pre>

Goto the example subdirectory and create <tt>calculatorImpl.java</tt> file as follows.

<pre>
package example;

import example.calculatorPackage.numbers;

public class calculatorImpl extends calculatorPOA {

	public int add(numbers n) {
		return n.first + n.second;
	}

	public int subtract(numbers n) {
		return n.first - n.second;
	}
}
</pre>

Go back to the root directory (the directory where calculator.idl is located) and create <tt>Server.java</tt> as follows.

<pre>
import java.io.*;
import org.omg.CosNaming.NamingContextExt;
import org.omg.CosNaming.NamingContextExtHelper;
import example.calculatorImpl;

public class Server {
    public static void main(String[] args) {
        org.omg.CORBA_2_3.ORB orb = 
        	(org.omg.CORBA_2_3.ORB) org.omg.CORBA.ORB.init(args, null);
        try {
            org.omg.PortableServer.POA poa = 
            	org.omg.PortableServer.POAHelper.narrow(
            			orb.resolve_initial_references("RootPOA"));
            poa.the_POAManager().activate();
            org.omg.CORBA.Object o = 
            	poa.servant_to_reference(new calculatorImpl());
            if(args.length == 1) {
                PrintWriter ps = new PrintWriter(new FileOutputStream(args[0]));
                ps.println(orb.object_to_string(o));
                ps.close();
            } else {
                NamingContextExt nc = 
                	NamingContextExtHelper.narrow(
                			orb.resolve_initial_references("NameService"));
                nc.bind(nc.to_name("calculator"), o);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        orb.run();
    }
}
</pre>

Compile all the Java classes by using the following command.
<pre>javac *.java</pre>

<h3>Creating the CORBA web service</h3>
Now we are ready to create a CORBA web service using the Axis2 CORBA module. First of all we have to prepare Axis2 to work with CORBA module.
<br /><br />
1. Make sure axis2-corba-{version}.jar is available in AXIS2_HOME/lib directory.
<br /><br />
2. Download latest Apache Yoko binary distribution form http://cwiki.apache.org/YOKO/download.html. Extract the downloaded archive to a temporary directory and copy yoko-core-{version}.jar and yoko-spec-corba{version}.jar to AXIS2_HOME/lib directory. (Axis2 CORBA module can also work with other CORBA implementations. Refer 'Additional Configuration Details' section for more information.)
<br /><br />
3. Add the following line to the &lt;axisconfig&gt; section of the axis2.xml file which is located in AXIS2_HOME/conf directory.<br />
<pre>&lt;deployer extension=".xml" directory="corba" class="org.apache.axis2.corba.deployer.CorbaDeployer"/&gt;</pre>
<br />
4.Create a new directory named corba inside  AXIS2_HOME/repository directory.
<br /><br />

Now, your Axis2 server is ready to deploy CORBA web services. Copy calculator.idl file to the newly created corba directory and create a new file named <tt>calculator.xml</tt> as follows inside the same directory.

<pre>
&lt;service name="Calculator">
    &lt;description&gt;Calculator Service&lt;/description&gt;
    &lt;parameter name="idlFile"&gt;calculator.idl&lt;/parameter&gt;
    &lt;parameter name="interfaceName"&gt;example::calculator&lt;/parameter&gt;
    &lt;parameter name="namingServiceUrl"&gt;corbaloc::localhost:900/NameService&lt;/parameter&gt;
    &lt;parameter name="objectName"&gt;calculator&lt;/parameter&gt;
&lt;/service&gt;
</pre>

Running the Example

Start a console window and execute the following command to start the CORBA name service.
<pre>tnameserv -ORBInitialPort 900</pre>

Start an other console window and goto the directory where Server.java is located. Execute the following command to start the CORBA server.
<pre>java Server</pre>

Start the Axis2 server. The EPR of the new Calculator web service will be <tt>http://localhost:8080/axis2/services/Calculator</tt>. The WSDL is located at <tt>http://localhost:8080/axis2/services/Calculator?wsdl</tt>. Now you can create a web service client and use it to invoke methods on the CORBA server.

<h3>Additional Configuration details</h3>
The service definition file (eg. calculator.xml) supports the following parameters.
<br />

<table>
<tr>
<th>Parameter Name</th>
<th>Description</th>
<th>Required</th>
</tr>
<tr>
<td>idlFil</td>
<td>Relative path to the IDL file</td>
<td>Yes</td>
</tr>
<tr>
<td>orbClass</td>
<td>Overrides the default orb class name.</td>
<td>No</td>
</tr>
<tr>
<td>orbSingletonClass</td>
<td>Overrides the default orb singleton class name.
(Default: org.apache.yoko.orb.CORBA.ORB)</td>
<td>No</td>
</tr>
<tr>
<td>namingServiceUrl</td>
<td>URL of the CORBA naming service
(Default: org.apache.yoko.orb.CORBA.ORBSingleton)</td>
<td>No</td>
</tr>
<tr>
<td>iorFilePath</td>
<td>Path to IOR file</td>
<td>No</td>
</tr>
<tr>
<td>iorString</td>
<td>IOR as a string</td>
<td>No</td>
</tr>
<tr>
<td>objectName</td>
<td>Name of the CORBA service which used in the naming service
Required if namingServiceUrl is present
interfaceName
Full name of the IDL interface used for the web service. (use :: as the separator between module and interface names)</td>
<td>Yes</td>
</tr>
</table>

<br />
<h3>Notes:</h3>
1. Axis2 CORBA module uses Apache Yoko as the default CORBA implementation. If you want to use a CORBA implementation other than Apache Yoko, override orbClass and orbSingletonClass properties.
<br /><br />
2. To run the above tutorial without a naming service:<br />
		Use <tt>java Server /path/to/a/new/file</tt> to start the server. Remove <tt>namingServiceUrl</tt> and <tt>objectName</tt> properties from the <tt>calculator.xml</tt> file and add the following line to the 	same file.
		<pre>&lt;parameter name="iorFilePath"&gt;/path/to/a/new/file&lt;/parameter&gt;</pre>
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