Embedding Apache Axis2 into Existing Applications
On this site, I have covered different topics on Axis2 that go from an introduction to Axis2 to very advanced tasks with Axis2, such as data services with Axis2. In this article, I am not going to discuss how to use Axis2 in simple applications or writing a service using Axis2; for that, I would recommend you to follow a few previous articles. The main goal of this article is to explain how to deploy or integrate Axis2 into an existing application.
There are a number of ways that one can use Axis2, and that can be easily divided in to two main categories. Which is Axis2?
- As a client to invoke other services
- To well deploy Web services
In both of those approaches, developers can use Axis2 as a standalone or integrate it into an existing application. I have already discussed how to use Axis2 as a standalone application, both as a client an as a server, in previous articles. You can find those by using the site's search engine.
Axis2 as a Standalone Client
In this case, your requirement is to invoke a remote Web service using Axis2. To use Axis2 as a standalone client, the only thing you need to do is add Axis2 and dependent third-party libraries into class path, or set up your favorite IDE with Axis2 and dependent libraries. Simply add Axis2 and depended libraries into the IDE. After doing either of these two, you can use Axis2 to invoke a remote service.
Even if youe are going to integrate Axis2 into an existing application as a client, there would not be much difference. You just need to add Axis2 and depended libraries to the existing application and then call the Axis2 client API for the application.
Axis2 as a Standalone Server
In this case, the meaning of standalone is not as an integrated application. Axis2 comes with a built-in HTTP server as well as an application server-based deployment. In the case of a simple HTTP server, you just need to download the Axis2 binary distribution and run "axis2server.bat" in Windows and "axis2server.sh" in a Linux environment. Then, Axis2 will start a simple HTTP server so you can use that as your Web service server to deploy and access Web services.
In the case of an application server deployment, you need to download the Axis2 .war distribution and copy that into the application server. If you take Tomcat as an example, you need to copy the axis2.war file into the webapps directory. If Tomcat is running, it will deploy Axis2 automatically; otherwise, you need to start Tomcat. In either case, Tomcat will act as the server and, when there is a request, it will dispatch that request to Axis2.
The question is how to deploy services in any of the above cases. Deploying a service in either case is just a matter of copying the service archive file into the repository/services directory. If you take a simple HTTP server as an example, you need to put your services into "repository/services" in the case of Tomcat or, in any other application server, you need to copy the service into the "WEB-INF/services" directory.
Embedding Axis2 into an Existing Application
You've now learned how to install Axis2 as a standalone and to deploy the service into Axis2. Now, see how you are going to embed or integrate Axis2 into an existing application. Here, you are going to learn how to embed Axis2 into a J2EE application. As an example application, you are going to deploy on a J2EE application server or another application server, such as Tomcat.
The first part of embedding Axis2 is setting up the transport front; this means to configure the servlet. The Axis2 main servlet is "AxisServlet". Remember that there is one thing you need to keep in mind when adding the servlet mapping. First, see how you add the servlet in the web.xml; for that, you need to add the following XML tag in the application's web.xml.
<servlet> <servlet-name>AxisServlet</servlet-name> <display-name>Apache-Axis Servlet</display-name> <servlet-class> org.apache.axis2.transport.http.AxisServlet </servlet-class> <load-on-startup>1</load-on-startup> </servlet>
Then, add the servlet mapping:
<servlet-mapping> <servlet-name>AxisServlet</servlet-name> <url-pattern>/services/*</url-pattern> </servlet-mapping>
If you add the servlet mapping like this (url-pattern with "services"), you do not need to do any other modification. However, if you do not like having the mapping as "services", you need to do one more step. Say you want to change the servlet mapping to "applications"; your mapping will look like that below:
<servlet-mapping> <servlet-name>AxisServlet</servlet-name> <url-pattern>/applications/*</url-pattern> </servlet-mapping>
Then, as mentioned before, you will need to change axis2.xml as well. There, you need to add the following parameter in to axis2.xml to have the correct servlet mapping.
I will soon discuss the location of axis2.xml, as well how to change its location.
Adding a Service and Modules
Once you do the configuration to web.xml, at the system startup time it will initialize AxisServlet, and then it will try to load the services from the default location. Here, the assumption is that the default repository is the WEB-INF directory. So, Axis2 will try to load the services from "WEB-INF/services" and modules of service extension from "WEB-INF/modules". In addition to that, the default axis2.xml will load from "WEB-INF/conf/axis2.xml".
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