XML Reference Guide

Mar 14, 2003

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One of the great features designed into Web services has been the notion that you can create a service automatically; in other words, you can type a few commands, and automatically create a client for service you want to access. This single capability is perhaps the greatest reason Web services are taken off as they have; without it, we'd all have to hand code to a fairly complicated specification.

So any tool that makes it easier to create clients is welcome; one that also allows us to easily create services is even more welcome. This month saw the release of Apache Axis2 1.0. The successor to the popular Apache Axis project, Axis2 has been completely rebuilt from the ground up. It includes the following features:

Support for SOAP 1.1, SOAP 1.2, and REST
Support for WSDL code generation, and no matter what the encoding/style
Support for all message exchange patterns
Support for both synchronous and asynchronous service clients
Hot deployment of both the application and services
The ability to obtain a service's WSDL, schema, and even policies easily
Support for multiple transports, including HTTP, JMS, SMTP, and TCP

Axis2 also includes support for other standards, such as:

Apache's new object model, AXIOM
WS-Addressing (both the submission and final versions)
WS-Policy
WS-ReliableMessaging
WS-Coordination
WS-AtomicTransaction
WS-Security
WS-Addressing

Axis2 is built on a modular structure, enabling extension usually modules that can be enabled or disabled at both the application and the service-level. For example, at the time of this writing, modules provide support for the following recommendations:

WS-ReliableMessaging
WS-Coordination
WS-AtomicTransaction
WS-Security
WS-Addressing

All right, so how do you actually do something with Axis2? Let's start with how easy it is to create an actual service. Consider, for example, a simple Java class:

package com.informit.xmlguide.candy;

public class InventoryService{

    public OMElement getInventory(OMElement prodInfo){
       //Extract product number from prodInfo element and
       //return current inventory as an element
    }

    public void updateInventory(OMElement invInfo){
       //Extract the product number and new inventory 
       //value from invInfo element and act on it.
    }

}

This is a simple class, with just two methods. The first, getInventory(), is a traditional request-response method. You send it information in the form of an OMElement -- part of the AXIOM framework, this is essentially just an XML element -- and it does some processing and returns another OMElement. The second, updateInventory(), is an "in only" request, in that it doesn't return any information at all.

The process of turning this into a Web service is pretty straightforward. Once we have a class that compiles, virtually all we need is a service.xml file:

<service>
    <description>

        This is the inventory service, providing opportunities to 
        both update and request inventory information.
    </description>
    <parameter name="ServiceClass" locked="false">com.informit.xmlguide.candy.InventoryService</parameter>
    <operation name="getInventory">
        <messageReceiver class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/>

        <actionMapping>urn:getInventory</actionMapping>
    </operation>
     <operation name="updateInventory">
        <messageReceiver class="org.apache.axis2.receivers.RawXMLINOnlyMessageReceiver"/>

        <actionMapping>urn:updateInventory</actionMapping>
    </operation>
 </service>

The service.xml file tells Axis2 about the service. It points out the class and the methods to be turned into operations. It also specifies whether the service should use a "in-out" receiver, or an "in only" receiver.

To actually deploy the service, you will need a "Axis2 Archive file", or .aar. Don't panic, though, it's just a jar file. To create it, lay out your files as follows:

/service
    /META-INF
        service.xml
    InventoryService.class

You can then execute the following command from the serivce directory:

jar -cf InventoryService.aar .

Deploying the service is a matter of uploading it to the Axis2 application. The application, which comes packaged as the axis2.war file, must be deployed to a container such as Apache Tomcat or Apache Geronimo. From there, access the Axis2 administration application by pointing your browser to:

http://localhost:8080/axis2

Click the "Administration" link and log in with the default information, admin/axis2. The Administration page gives you the opportunity to control many aspects of the Axis2 application, including service parameters and modules. It also gives you the opportunity to "hot deploy" a service to the running application without having to restart the web application server.

Click "Upload service" and browse to the .aar file you created earlier. Click "Upload". You can see the new service by clicking on the "Available sources" link:

Notice that not only did Axis2 create the service, it created both a SOAP service and a REST service.

Axis2 also enables you to easily create services and clients from WSDL files. For example, if we had started with a WSDL file instead of a Java class, we could create the service by running the WSDL2Java script, located in the axis2/bin directory:

WSDL2Java -uri InventoryService.wsdl -ss -sd -p com.informit.xmlguide.candy
-d xmlbeans -o service

In this case, we are telling the script to take the inventoryService.wsdl file and generate both the server side and service description files, placing the classes in the com.informit.xmlguide.candy package and using Apache's xmlbeans as the data binding method. The output goes to the service directory.>

This process can generate over 200 files, but the only one you're worried about is the "skeleton" file, in which you implement the actual service. For example:

package com.informit.xmlguide.candy;

public class InventoryServiceSkeleton{

    public  com.informit.xmlguide.candy.xsd.GetInventoryReturnDocument getInventory (com.informit.xmlguide.candy.xsd.GetInventoryParamDocument param0 )
         
    {
          //Implement the service here using data binding
          //and return a GetInventoryReturnDocument object
    }
     
    public  void updateInventory (com.informit.xmlguide.candy.xsd.UpdateInventoryParamDocument param2 )
         
    {
        //Implement the service
    }
     
}

Once you implement the service, you need to create the .aar file:

set ANT_HOME=e:\apache-ant-1.6.5
PATH=%PATH%;%ANT_HOME%\bin;
set AXIS2_HOME=e:\axis2
cd service
ant jar.service

As I said, the generation process creates a large amount of files, so you wouldn't want to have to compile them by hand. Fortunately, the generation process also creates a build.xml file for Apache Ant to use to compile the service. The end result is the InventoryService.aar file, which you deploy as before.

Creating a client can be just a simple. Again, you can use the WSDL2Java script:

WSDL2Java -uri ClassifiedService.wsdl -p com.informit.xmlguide.candy -d xmlbeans -o client

In this case, the important file is the "stub", which you can then use to create a client, as in:

package com.informit.xmlguide.candy;

import axis2.apache.org.xsd.*;

public class CandyClient{

   public static void main(java.lang.String args[]){

      try{
         InventoryServiceStub stub = 
              new InventoryServiceStub(null,
     "http://localhost:8080/axis2/services/InventoryService");
            
         GetInventoryRequestDocument invReqDoc = 
               GetInventoryRequestDocument.Factory.newInstance();

         GetInventoryRequestDocument.GetInventoryRequest invReq = 
                              invReqDoc.addGetInventoryRequest();
         invReq.setProductID("THX1138");
 
         GetInventoryResponseDocument invResDoc = 
                                       stub.getInventory(invReqDoc);
         System.out.println("Inventory:  "+
                invResDoc.getGetInventoryResponse().getInventory());

      } catch(Exception e){
         e.printStackTrace();
      }
   }
}

These classes are generated by the WSDL2Java script. The client can also be compiled by Ant, this time using the jar.client target.

Of course, this is just a cursory look at what Apache Axis2 can do. For more information, check out the resources that follow.

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