a cup of java

I used to put some stupid test cases to unit-test my code and I usually don’t forget to remove ‘em before review. But last time when my customer reviewed my code, he found the following segment at the end of a Java file. He laughed and asked “Is that true Subin?”

//------------------------ Test methods ---------------------------

static class TestClass
{
 public TestClass(String name)
 {
 this.name = name;
 }

 private String name;

 @Override
 public boolean equals(Object anObject)
 {
 return (true);
 }

 @Override
 public int hashCode()
 {
 return (1);
 }
}

public static void main(String[] args)
{
 Set<TestClass> aSet = new HashSet<TestClass>();
 aSet.add(new TestClass("Subin "));
 aSet.add(new TestClass("is in "));
 aSet.add(new TestClass("a "));
 aSet.add(new TestClass("big "));
 aSet.add(new TestClass("big "));
 aSet.add(new TestClass("trouble"));

 System.out.println(aSet.size());
}

In my previous post I wrote about writing a web service provider using axis. But I did not mention a few things in that post.

1. How to make the service accessible to the outside world
2. How to write a Java client to avail the services

1. How to make the service accessible to the outside world?

As we are using the axis2.war as the way to deploy the services, we don’t really need to do anything. The deployment descriptor (web.xml) of axis2.war is equipped to handle it. But we need to make some URL mapping and stuffs like that.

- Add appropriate URL-servlet mapping  in the web.xml
- Add the name of the AAR in the service list

a. Deployment descriptor changes:

 <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>

 <servlet-mapping>
   <servlet-name>AxisServlet</servlet-name>
   <url-pattern>/servlet/AxisServlet</url-pattern>
 </servlet-mapping>

 <servlet-mapping>
   <servlet-name>AxisServlet</servlet-name>
   <url-pattern>/services/*</url-pattern>
 </servlet-mapping>

b. Add the name of the AAR in WEB-INF/services/services.list.

2. Writing a Java client to access the services

We have several ways to create the client stubs – JiXB, ADB etc. I followed ADB – Axis Data Binding. Axis provides a WSDL2Java tool to create client stubs from an existing WSDL. We can get the WSDL from http://localhost/services/SampleWs?wsdl.

WSDL2Java -uri SampleWs.wsdl -p subin.rnd.ws.client -d adb -s -o clientStubSrcDirectory_name

This will create the stub in the specified directory with name SampleWsStub.java. Once the stub is ready, we can write a client module which tries to access the deployed services.

WsClient.java

package subin.rnd.ws.client;

import subin.rnd.ws.client.SampleWsStub.WsInput;
import subin.rnd.ws.client.SampleWsStub.WsOutput;

public class WsClient
{
 public static void main(String[] args)
 throws Exception
 {
   SampleWsStub stub = new SampleWsStub("http://localhost/services/SampleWs");

   // Send the request
   SampleWsStub.DoSomething request = new SampleWsStub.DoSomething();
   WsInput anInput = new WsInput();
   anInput.setName("subin");
   request.setAnInput(anInput);

   // Get the response
   SampleWsStub.DoSomethingResponse response = stub.doSomething(request);
   WsOutput anOutput = response.get_return();

   System.out.println(anOutput.getResponseString());
 }
}

And that’s it !!!

This is a very basic post on writing a web service provider and consumer using Axis2. You can find such posts anywhere in the web. Here I’ve tried to make it as simple as I can.

Set up: What all we need to do?

1. Axis2 runtime.
I tried with WAR distribution from http://ws.apache.org/axis2/download/1_5/download.cgi
2. A web/app server. I am using Tomcat.

Using the Axis2 runtime & setting it up

Extract the Axis2 WAR distribution and keep it in the deploy directory of the server. In case of Tomcat keep it in webapps. This is how my directory structure look like.

The WEB-INF is the most important directory. Tell you why. Unlike our normal WEB-INF in archives, this directory hold some special sub-directories. Here goes which contains what.

classes – compiled Java classes. We can find some Axis specific classes here.
conf – axis.xml (Axis configuration file)
lib – All necessary Axis2 libraries (JARs)
modules – Don’t ask me. Even I’m not sure. Did I mention that I’m also a beginner?
services – All web service archives & services.list

Coding: What we need to write?

1. The service provider. A Java class.
2. service.xml. The web services descriptor.
3. build.xml. To build and deploy the web services archive.
4. The service consumer. Another Java class to consume the services offered

And we are good to go now. Let’s make our hands dirty with some Java code. This is very simple and kudos to Axis2.

The service provider: SampleService.java

package subin.rnd.ws;
public class SampleService
{
  public WsOutput doSomething(WsInput anInput)
  {
    System.out.println("doSomething()");
    WsOutput anOutput = new WsOutput();
    anOutput.setResponseString("I did some thing to " + anInput.getName());
    return (anOutput);
 }
}

WsInput is a sample input class to demonstrate that we can have more complex IO is possible. Similarly WsOutput is the output class. Instead of using WsInput / WsOutput for IO, we can use normal data types like integer, float, string etc too.

WsInput.java

package subin.rnd.ws;
import java.io.Serializable;
public class WsInput implements Serializable
{
 private String name;
 public void setName(String name)
 {
   this.name = name;
 }

 public String getName()
 {
   return (this.name);
 }
}

WsOutput.java

package subin.rnd.ws;
import java.io.Serializable;
public class WsOutput implements Serializable
{
 private String responseString;

 public void setResponseString(String response)
 {
   this.responseString = response;
 }
 public String getResponseString()
 {
   return (this.responseString);
 }
}

We have the Java part of the web-service ready. But that’s not enough. We need to deploy the web-service as an AAR – Axis Archive – file. An AAR  is just another zip file (like a JAR) with a funky extension . The AAR should contain the class files along with the services.xml – web service descriptor.

Web service descriptor: services.xml

<service name="SampleWs" scope="application">
 <description>Subin's sample webs service</description>
 <messagereceivers>
 <messagereceiver mep="http://www.w3.org/2004/08/wsdl/in-only"
 class="org.apache.axis2.rpc.receivers.RPCInOnlyMessageReceiver"/>
 <messagereceiver mep="http://www.w3.org/2004/08/wsdl/in-out"
 class="org.apache.axis2.rpc.receivers.RPCMessageReceiver"/>
 </messagereceivers>
 <operation name="doSomething" />
<parameter name="ServiceClass">subin.rnd.ws.SampleService</parameter>
</service>

The services.xml is the place where we define the details of the services being offered.

Build file: build.xml

<project name="my.webservice.test" default="build.aar">
<property name="deploy.dir" value=".../webapps/axis2.war/WEB-INF/services" />
<property name="file.name" value="subinws.aar" />

 <target name="build.aar">
   <javac srcdir="src" destdir="bin" />
   <echo>Copying services.xml to bin</echo>
   <copy file="META-INF/services.xml"
       tofile="bin/META-INF/services.xml" overwrite="true"/>
   <jar basedir="bin" destfile="${file.name}" />
   <echo>Deleting services.xml from bin</echo>
   <delete dir="bin/META-INF" />
   <copy file="${file.name}" tofile="${deploy.dir}/${file.name}"  />
 </target>

</project>

So I hope we have an AAR ready, which is copied to the services directory. But we’ve not done yet. Now we have to make an entry in services/services.list file. Just insert the name of the ARR file at the end of it – in this case “subinws.aar”.

Please wait for part 2.

I was just going through code.google.com, and just find a link titled “App Engine”. I was not at all surprised as they do this every time. With Google something is new every time. I went on reading. Oh God! Free J2EE app engine where we can host our archives ! This is one of the coolest things I was waiting to happen. The server where I hosted (and I’m still with them) my website does not have Java support and I spend many hours in writing Php codes after many hours of searching and testing, which I could have done in minutes with Java. And most importantly it’s almost FREE ! We have to pay them only if we are crossing the specified bandwidth & page view limits.

We can write code with Google’s Eclipse plug-in (with GWT support !), test them with in Eclipse and deploy them from Eclipse! Isn’t that cool? All you need is to have a Google account and just get it done. We can have up to nine applications each with a unique URL to access and we can even link them with our Google Apps too.

Check this video: Get an overview of App Engine’s new Java runtime and see a demo of a sample app from creation to deployment.

URL: http://www.youtube.com/watch?v=P3GT4-m_6RQ

-
For me this is nicest offer from Google in the recent times. I don’t know whether all of you are going to agree with this. But at least I’m happy. Hope all of you will find it nice.

Google App Engine: http://code.google.com/appengine/
FAQ: http://code.google.com/appengine/kb/
App Engine Blog: http://googleappengine.blogspot.com/
Getting started: http://code.google.com/appengine/docs/java/gettingstarted/

This is about another exception you may get while playing around with JBoss, Transactions, Remote EJBs etc. And the exception is:

org.jboss.resource.JBossResourceException:
Could not enlist in transaction on entering meta-aware object!

My friend Venu had a post in his blog on why this exception happens and how to fix it in JBoss 5.0. You can read it here. But if we are using JBoss 5.1.0 this solution cannot help us. Because there are a couple of changes in the configuration in this new version of JBoss. In fact if you can take a look at the JBoss 5.1.0 GA release notes we can see a lot of changes in configuration especially if we are migrating from JBoss 5.0 to 5.1.

And here is the solution.

Open the JBOSS_HOME/server/JBOSS_CONFIGURATION/conf/jbossts-properties.xml. Set the following.

<!-- Support subtransactions in the JTA layer? Default is NO. -->
<property name="com.arjuna.ats.jta.supportSubtransactions" value="YES"/>

Hope this helps.

P.S. If you have any more details in this issue, please feel free to share it. Thank you.