| <?xml version="1.0" encoding="iso-8859-1"?>
|
|
|
| <!--
|
| ~ Licensed to the Apache Software Foundation (ASF) under one
|
| ~ or more contributor license agreements. See the NOTICE file
|
| ~ distributed with this work for additional information
|
| ~ regarding copyright ownership. The ASF licenses this file
|
| ~ to you under the Apache License, Version 2.0 (the
|
| ~ "License"); you may not use this file except in compliance
|
| ~ with the License. You may obtain a copy of the License at
|
| ~
|
| ~ http://www.apache.org/licenses/LICENSE-2.0
|
| ~
|
| ~ Unless required by applicable law or agreed to in writing,
|
| ~ software distributed under the License is distributed on an
|
| ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
|
| ~ KIND, either express or implied. See the License for the
|
| ~ specific language governing permissions and limitations
|
| ~ under the License.
|
| -->
|
|
|
| <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
|
| "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
|
| <html xmlns="http://www.w3.org/1999/xhtml">
|
| <head>
|
| <meta http-equiv="content-type" content=
|
| "text/html; charset=us-ascii" />
|
| <title>Exposing CORBA Services as Web Services</title>
|
| </head>
|
| <body xml:lang="en">
|
| <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 <axisconfig> section of the axis2.xml file which is located in AXIS2_HOME/conf directory.<br /> |
| <pre><deployer extension=".xml" directory="corba" class="org.apache.axis2.corba.deployer.CorbaDeployer"/></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> |
| <service name="Calculator"> |
| <description>Calculator Service</description> |
| <parameter name="idlFile">calculator.idl</parameter> |
| <parameter name="interfaceName">example::calculator</parameter> |
| <parameter name="namingServiceUrl">corbaloc::localhost:900/NameService</parameter> |
| <parameter name="objectName">calculator</parameter> |
| </service> |
| </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><parameter name="iorFilePath">/path/to/a/new/file</parameter></pre> |
| </body> |
| </html> |
| |