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<h1>POJO Web Services using Apache Axis2</h1>
<p>Want a quick way to get a Web service up and running in no time? Well
then, you should consider creating a Plain Old Java Object (POJO) to deploy
using Apache Axis2 on Apache Tomcat. POJOs are fast to build and easy to
maintain, meaning you'll save a lot of time building and debugging your code.
This document shows you how to take a simple POJO, and deploy it on Apache
Tomcat as a Web service in the exploded directory format. You'll also be
shown how to take a POJO based on the Spring Framework, and deploy that as an
AAR packaged Web service on Tomcat.</p>
<h2>Content</h2>
<ul>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#pojo">The POJO</a></li>
<li><a href="#pojows">POJO Web service using Apache Axis2 and Tomcat</a>
<ul>
<li><a href="#definingservice">Defining the Service:
services.xml</a></li>
</ul>
</li>
<li><a href="#buildpojows">Building the POJO Web Service Using Ant</a></li>
<li><a href="#testingpojows">Testing the POJO Web Service Using
RPCServiceClient</a>
<ul>
<li><a href="#limitationspojo">Limitations and Strengths of
POJO</a></li>
</ul>
</li>
<li><a href="#springpojows">Spring-based POJO Web Service</a>
<ul>
<li><a href="#quickintro">Quick Introduction</a></li>
<li><a href="#servicedef">The Service Definition: services.xml</a></li>
<li><a href="#initializingspring">Initializing the Spring application
context: SpringInit</a></li>
<li><a href="#testingrpc">Testing Using an RPCServiceClient</a></li>
</ul>
</li>
<li><a href="#summary">Summary</a></li>
<li><a href="#furtherstudy">For Further Study</a></li>
</ul>
<a name="introduction"></a>
<h2>Introduction</h2>
<p>The task of building a Web service can sometimes be overwhelming, but not
with POJOs! The old-school Plain Old Java Object is a simple and quick way to
get most, if not all, of your currently existing Java classes up on the Web
as readily accessible Web services. This document will show you how to build
a POJO-style Web service with Apache Axis2 and Tomcat, organized as
follows:</p>
<ul>
<li>The POJO: This is the Java class that you'll use throughout this
document</li>
<li>POJO deployment</li>
<li>Test the POJO Web service using an RPC based client</li>
<li>Limitations of straight POJO</li>
<li>Spring-based POJO Web service and deployment</li>
</ul>
<p>The code for the document can be found at Axis2_HOME/samples/pojoguide
&amp; Axis2_HOME/samples/pojoguidespring once you extract the <a
href="../../download/1_1/download.html#std-bin">Axis2 Stadard
Distribution</a>, and it might help to go grab it now to help you as you
follow along. Let's get started.</p>
<a name="pojo"></a>
<h2>The POJO</h2>
<p>The POJO you'll be using throughout this document is a Weather service
POJO that consists of two classes: WeatherService and Weather. Weather
contains the Weather data: Temperature, forecast, rain (will it rain?), and
howMuchRain (See Code Listing 1).</p>
<p><b>Code Listing 1: The Weather POJO</b></p>
<pre>package sample.pojo.data;
public class Weather{
float temperature;
String forecast;
boolean rain;
float howMuchRain;
public void setTemperature(float temp){
temperature = temp;
}
public float getTemperature(){
return temperature;
}
public void setForecast(String fore){
forecast = fore;
}
public String getForecast(){
return forecast;
}
public void setRain(boolean r){
rain = r;
}
public boolean getRain(){
return rain;
}
public void setHowMuchRain(float howMuch){
howMuchRain = howMuch;
}
public float getHowMuchRain(){
return howMuchRain;
}
}</pre>
<p>And here's the WeatherService class, shown in Code Listing 2.</p>
<p><b>Code Listing 2: The WeatherService class</b></p>
<pre>package sample.pojo.service;
import sample.pojo.data.Weather;
public class WeatherService{
Weather weather;
public void setWeather(Weather weather){
this.weather = weather;
}
public Weather getWeather(){
return this.weather;
}
}</pre>
<p>Note that it's all just straight POJOs with field items and
<code>getter</code> and <code>setter</code> methods for each field. Next,
you'll take a look at what you need to do to make it ready for deployment on
Apache Axis2 and Tomcat.</p>
<a name="pojows"></a>
<h2>POJO Web Service Using Apache Axis2 and Tomcat</h2>
<p>Got the POJOs? Great. This section will show you how to package them in
the exploded directory format for easy deployment. First you'll look at the
services.xml file that defines the Web service, and then you'll build the
files using <a href="http://ant.apache.org/">Apache Ant</a>, and deploy the
Web service on Tomcat.</p>
<a name="definingservice"></a>
<h3>Defining the Service: services.xml</h3>
<p>Before Axis2 can understand what is going on, you have to tell it to use
the services.xml file. Let's get right into it (see Code Listing 3).</p>
<p><b>Code Listing 3: The service definition file: services.xml</b></p>
<pre>&lt;service name="WeatherService" scope="application"&gt;
&lt;description&gt;
Weather POJO Service
&lt;/description&gt;
&lt;messageReceivers&gt;
&lt;messageReceiver
mep="http://www.w3.org/2004/08/wsdl/in-only"
class="org.apache.axis2.rpc.receivers.RPCInOnlyMessageReceiver"/&gt;
&lt;messageReceiver
mep="http://www.w3.org/2004/08/wsdl/in-out"
class="org.apache.axis2.rpc.receivers.RPCMessageReceiver"/&gt;
&lt;/messageReceivers&gt;
&lt;parameter name="ServiceClass"&gt;
sample.pojo.service.WeatherService
&lt;/parameter&gt;
&lt;/service&gt;</pre>
<p>The name of the service is specified as WeatherService and the scope of
the service is application. As you can see in the WeatherService POJO, there
are two methods, an IN-ONLY method and a IN-OUT method, hence the ordering
for the messageReceiver elements within the messageReceivers tag. Lastly, the
ServiceClass parameter specifies the class of the Web service, which is
sample.pojo.service.WeatherService. When operations of your Web service get
called, the methods of the WeatherService class will be called. Next you'll
take a look at an easy method of building your application using Ant.</p>
<a name="buildpojows"></a>
<h2>Building the POJO Web Service Using Apache Ant</h2>
<p><a href="http://ant.apache.org/">Ant</a> is a slick build tool. It helps
reduce time to build applications, and several of the Axis2 command-line
tools create build.xml files for you, so that's why we'll use it here. We
won't go into the build.xml file that you'll be using in too much detail, so
here are the main Ant tasks you'll be using:</p>
<ul>
<li>generate.service -- This Ant task builds all the service relevant
source and copies the files to build/WeatherService</li>
<li>rpc.client -- This task builds the client relevant files, builds a JAR
at <em>build/lib/rpc-client.jar</em>, and then runs the client</li>
</ul>
<p>Before you can build the source, however, you'll need to download the
Axis2 1.1-bin and 1.1-war distributions <a
href="../../download/1_1/download.html">here</a>. Then modify the following
line inside the build.xml file (in the Axis2_HOME/samples/pojoguide directory
in the extracted Axis2 1.1 Standard Binary (bin) Distribution) :</p>
<pre>&lt;property name="axis2.home" value="c:\apps\axis2" /&gt;</pre>
<p>This modification contains the path to the root of the unzipped Axis2
1.1-bin <a href="../../download/1_1/download.html#std-bin">download</a>. With
that explanation, you'll now build the source by typing the following: ant</p>
<p>The following directory format should now exist at
build/WeatherService:</p>
<pre> - WeatherService
- META-INF
- services.xml
- sample
- pojo
- data
- Weather.class
- service
- WeatherService.class</pre>
<p>Simple isn't it? An excellent way to dive into Web services
development.</p>
<p>Now get a <a href="http://tomcat.apache.org/">Tomcat</a> distribution (I
used v5.5), and start it up by running <em>bin/startup.bat</em> or
<em>bin/startup.sh</em>. Once it's running, deploy the Axis2 1.1-war by
copying the axis2.war file to Tomcat's webapps directory. Tomcat will proceed
by deploying axis2 and un-archive it into the webapps directory. Now copy the
WeatherService directory created when building our project to:
<em>&lt;tomcat-home&gt;/webapps/axis2/WEB-INF/services</em>.</p>
<p>The service should quickly deploy, and you'll test the Web service using
the RPCServiceClient in the next section.</p>
<a name="testingpojows"></a>
<h2>Testing the POJO Web Service Using RPCServiceClient</h2>
<p>OK, so the Web service should be running on Tomcat. Now you'll build a
simple RPCServiceClient and test the POJO Web service. You'll first start out
with the class constructs, creating the RPCServiceClient and initializing the
values of the Weather class within the Web service (See Code Listing 4).</p>
<p><b>Code Listing 4: Setting the weather</b></p>
<pre>package sample.pojo.rpcclient;
import javax.xml.namespace.QName;
import org.apache.axis2.AxisFault;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.axis2.client.Options;
import org.apache.axis2.rpc.client.RPCServiceClient;
import sample.pojo.data.Weather;
public class WeatherRPCClient {
public static void main(String[] args1) throws AxisFault {
RPCServiceClient serviceClient = new RPCServiceClient();
Options options = serviceClient.getOptions();
EndpointReference targetEPR = new EndpointReference(
<b>"http://localhost:8080/axis2/services/WeatherService");</b>
options.setTo(targetEPR);
// Setting the weather
QName opSetWeather =
new QName("http://service.pojo.sample/xsd", "<b>setWeather");
Weather w = new Weather();
w.setTemperature((float)39.3);
w.setForecast("Cloudy with showers");
w.setRain(true);
w.setHowMuchRain((float)4.5);
Object[] opSetWeatherArgs = new Object[] { w };
serviceClient.invokeRobust(opSetWeather, opSetWeatherArgs);</b>
...</pre>
<p>The most interesting code to note is in bold font. Notice the targetEPR
variable you create, setting the endpoint reference to
http://localhost:8080/axis2/services/WeatherService. This is where you
deployed it on Axis2. You can also verify this by asking Axis2 to list its
services by going to the following URL:
http://localhost:8080/axis2/services/listServices.</p>
<p>Next the opSetWeather variable gets setup, pointing to the setWeather
operation. Then the Weather data gets created and initialized. Lastly, you
invoke the Web service, which initializes the weather data (you'll verify
this soon). Next you get back the weather data (see Code Listing 5).</p>
<p><b>Code Listing 5: Getting the weather data</b></p>
<pre>...
serviceClient.invokeRobust(opSetWeather, opSetWeatherArgs);
// Getting the weather
QName opGetWeather =
new QName("http://service.pojo.sample/xsd", "<b>getWeather");
Object[] opGetWeatherArgs = new Object[] { };
Class[] returnTypes = new Class[] { Weather.class };
Object[] response = serviceClient.invokeBlocking(opGetWeather,
opGetWeatherArgs, returnTypes);
Weather result = (Weather) response[0];
if (result == null) {
System.out.println("Weather didn't initialize!");
return;
}</b>
...</pre>
<p>First you set the operation in opGetWeather to getWeather. Then you create
an empty argument list. Note this time you expect something back from the Web
service, and so you create a list of return types. Then you invoke the Web
service using a blocking call and wait for the weather data to be returned to
you, and you place it in the result variable. Lastly, you make sure it isn't
null and that it was successfully initialized by the previous call to
setWeather. Now display the data to verify that it is indeed what you set it
to (see Code Listing 6).</p>
<p><b>Code Listing 6: Displaying the data</b></p>
<pre>...
return;
}
// Displaying the result
<b>System.out.println("Temperature : " +
result.getTemperature());
System.out.println("Forecast : " +
result.getForecast());
System.out.println("Rain : " +
result.getRain());
System.out.println("How much rain (in inches) : " +
result.getHowMuchRain());
}</b>
}</pre>
<p>You should receive the data shown in Code Listing 7.</p>
<p><b>Code Listing 7: Output from running the client</b></p>
<pre>rpc.client.run:
[java] Temperature : 39.3
[java] Forecast : Cloudy with showers
[java] Rain : true
[java] How much rain (in inches) : 4.5</pre>
<p>Excellent, you have a working POJO Web service! Next you'll quickly morph
this one into a Spring based POJO.</p>
<a name="limitationspojo"></a>
<h3>Limitations and Strengths of POJO</h3>
<p>We've covered the strengths of using POJO based Web services, but what
about any limitations? One main limitation of POJO based Web services is the
lack of initialization support (meaning that you have to go into your Web
service and initialize the values before the Web service is completely
useful), but you'll soon see how to overcome that limitation with a Spring
based POJO, covered next.</p>
<a name="springpojows"></a>
<h2>Spring-based POJO Web Service</h2>
<p>Spring is a hot framework for J2EE and makes bean usage a breeze. You'll
use it in this section to create a Spring based POJO Web service. For this
section you'll need the spring.jar from the latest 1.x Spring download.</p>
<a name="quickintro"></a>
<h3>Quick Introduction</h3>
<p>If you take a look at the source code of this document in
Axis2_HOME/samples/pojoguidespring (to see how the Spring based POJO Web
service is coded), you can see that the Weather class didn't change at all
and the WeatherService class only got its name changed to
WeatherSpringService.</p>
<p>You'll also notice an applicationContext.xml file, which we'll cover
later: it's used to setup the beans used in our Web service.</p>
<p>Now you might wonder what the SpringInit.java class is for: This service
is necessary, however, to initialize the Spring Framework's application
context.</p>
<p>The client is pretty much the same, except you won't use it to initialize
the Weather data in the Web service, since Spring does that for you using
Inversion of Control (IoC), which is covered next.</p>
<a name="servicedef"></a>
<h3>The Service Definition: services.xml</h3>
<p>Because the core POJOs didn't change, you'll move straight to the
services.xml file. It's a bit longer this time because it instantiates two
services in one file (see Code Listing 7).</p>
<p><b>Code Listing 7: Defining the services: services.xml</b></p>
<pre>&lt;serviceGroup&gt;
&lt;service <b>name="SpringInit"
class="sample.spring.service.SpringInit</b>"&gt;
&lt;description&gt;
This web service initializes Spring.
&lt;/description&gt;
<b>&lt;parameter name="ServiceClass"&gt;
sample.spring.service.SpringInit
&lt;/parameter&gt;
&lt;parameter name="ServiceTCCL"&gt;composite&lt;/parameter&gt;
&lt;parameter name="load-on-startup"&gt;true&lt;/parameter&gt;</b>
&lt;operation name="springInit"&gt;
&lt;messageReceiver
class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/&gt;
&lt;/operation&gt;
&lt;/service&gt;
&lt;service <b>name="WeatherSpringService</b>"&gt;
&lt;description&gt;
Weather Spring POJO Axis2 AAR deployment
&lt;/description&gt;
<b>&lt;parameter name="ServiceClass"&gt;
sample.spring.service.WeatherSpringService
&lt;/parameter&gt;
&lt;parameter name="ServiceObjectSupplier"&gt;
org.apache.axis2.extensions.spring.receivers.SpringAppContextAwareObjectSupplier
&lt;/parameter&gt;
&lt;parameter name="SpringBeanName"&gt;
weatherSpringService
&lt;/parameter&gt;</b>
&lt;messageReceivers&gt;
&lt;messageReceiver mep="http://www.w3.org/2004/08/wsdl/in-only"
class="org.apache.axis2.rpc.receivers.RPCInOnlyMessageReceiver"/&gt;
&lt;messageReceiver mep="http://www.w3.org/2004/08/wsdl/in-out"
class="org.apache.axis2.rpc.receivers.RPCMessageReceiver"/&gt;
&lt;/messageReceivers&gt;
&lt;/service&gt;
&lt;/serviceGroup&gt;</pre>
<p>You'll see a few familiar items in the above listing, and several changes.
Once again, the items in bold are most important. The ServiceTCCL property
under the SpringInit service makes sure that the Spring class loader is used
for the Web service, allowing it to properly instantiate the Spring
application context. The load-on-startup variable is a must-have so that the
service loads up immediately on startup, creating the Spring application
context. The WeatherSpringService stays mostly the same to the WeatherService
previously with a couple additions: The ServiceObjectSupplier provides the
service with the Spring application context, making it "Spring Aware."</p>
<p>Lastly, the SpringBeanName points to the name of the bean associated with
this Web service, which is defined in the applicationContext.xml file
(essentially the WeatherSpringService). We'll cover the
applicationContext.xml file next. The application context:
applicationContext.xml file tells the Spring Framework, what beans are
defined. For this example, you'll define three of them (see Code Listing
8).</p>
<p><b>Code Listing 8: Defining the application context:
applicationContext.xml</b></p>
<pre>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd"&gt;
&lt;beans&gt;
&lt;bean id="<b>applicationContext</b>" class=
"org.apache.axis2.extensions.spring.receivers.ApplicationContextHolder" /&gt;
<b>&lt;bean id="weatherSpringService"
class="sample.spring.service.WeatherSpringService"&gt;
&lt;property name="weather" ref="weatherBean"/&gt;
&lt;/bean&gt;
&lt;bean id="weatherBean" class="sample.spring.bean.Weather"&gt;
&lt;property name="temperature" value="89.9"/&gt;
&lt;property name="forecast" value="Sunny"/&gt;
&lt;property name="rain" value="false"/&gt;
&lt;property name="howMuchRain" value="0.2"/&gt;
&lt;/bean&gt;</b>
&lt;/beans&gt;</pre>
<p>The first one is Axis2's hook into Spring's application context (needed
since AAR deployment is quite different from regular WAR deployment). Next,
you define the bean pointed to by the services.xml file, the
weatherSpringService bean that points to the WeatherSpringService class. It
has one field property that gets initialized by the Spring Framework,
weather, which will be set to the weatherBean. The weatherBean is an
instantiation of the Weather class that holds information on the weather.
Spring will initialize it to the values shown above, and set the Weather
object in the WeatherSpringService class to this weatherBean instantiation.
Thus, when you deploy the Web service you won't have to instantiate the
values because they'll already be set.</p>
<p>Next up is the SpringInit class.</p>
<a name="initializingspring"></a>
<h3>Initializing the Spring application context: SpringInit</h3>
<p>Without the Spring application context being initialized quickly, you'll
run into problems. The SpringInit class initializes the Spring application
context on startup because it is a ServiceLifeCycle class, whose startUp
method gets called upon loading the class (and because its load-on-startup
property is set in the serices.xml file). The only code worth mentioning in
this class is shown in Code Listing 9.</p>
<p><b>Code Listing 9: SpringInit's startUp method</b></p>
<pre> public void startUp(ConfigurationContext ignore,
AxisService service) {
<b>ClassLoader classLoader = service.getClassLoader();
ClassPathXmlApplicationContext appCtx = new
ClassPathXmlApplicationContext</b>(new String[]
{"<b>applicationContext.xml</b>"},
false);
<b>appCtx.setClassLoader(classLoader);
appCtx.refresh();</b>
if (logger.isDebugEnabled()) {
logger.debug("\n\nstartUp() set spring classloader " +
"via axisService.getClassLoader() ... ");
}
}</pre>
<p>Note that this method retrieves the Spring class loader, creates an
application context with applicationContext.xml as the parameters. This new
application context then gets the Spring class loader as its class loader.
The Spring Framework is now up and ready for our WeatherSpringService.</p>
<h3>Build and Deploy Using Apache Axis2 and Tomcat</h3>
<p>Great, your POJO is now ready for primetime within the Spring Framework.
Before you build, you'll first need to make sure the axis2-spring-1.1.jar and
spring.jar files are in the project's <em>Axis2_HOME/lib</em> directory.</p>
<p><strong>Note:</strong> The service will not deploy if you add the above jars files to the service archive due to cloass loding issues.</p>
<p>Now build the source and create an AAR file by typing:
ant</p>
<p>It'll be created at <em>target/WeatherSpringService.aar</em>. Copy it over
to <em>&lt;tomcat-home&gt;/webapps/axis2/WEB-INF/services</em>, and Axis2
should deploy it quickly.</p>
<p>Next test the Web service to see if Spring really will initialize the
weather data for you.</p>
<a name="testingrpc"></a>
<h3>Testing Using an RPCServiceClient</h3>
<p>It's as simple as it was for the other Web service, except this time type:
ant rpc.client</p>
<p>Feel free to browse the code for this client in
src/client/WeatherSpringRPCClient.java. Essentially, this client does the
exact same thing as the client testing the WeatherService, except this one
skips the "Setting the weather" task since the weather data should already
have been set by the Spring framework at startup.</p>
<p>Thus, you should get the following as output from the client:</p>
<pre>run.client:
[javac] Compiling 1 source file to C:\axis2-1.1\samples\pojoguidespring\build\cl
asses
<b>[java] Temperature : 89.9
[java] Forecast : Sunny
[java] Rain : false
[java] How much rain (in inches) : 0.2</b></pre>
<p>Which is exactly the values you set them to be in the
applicationContext.xml file!</p>
<a name="summary"></a>
<h2>Summary</h2>
<p>Apache Axis2 is an excellent way to expose your POJOs as Web services, and
Spring adds greater flexibility to your POJOs by adding beans support and
initialization abilities, along with all the other goodies provided by the
Spring framework.</p>
<a name="furtherstudy"></a>
<h2>For Further Study</h2>
<p>Apache Axis2-<a
href="http://ws.apache.org/axis2/">http://ws.apache.org/axis2/</a></p>
<p>Axis2 Architecture-<a
href="http://ws.apache.org/axis2/1_0/Axis2ArchitectureGuide.html">http://ws.apache.org/axis2/1_0/Axis2ArchitectureGuide.html</a></p>
<p>Introduction to Apache Axis2-<a
href="http://www.redhat.com/magazine/021jul06/features/apache_axis2/">http://www.redhat.com/magazine/021jul06/features/apache_axis2/</a></p>
<p>Working With Apache Axis2-<a
href="http://www.wso2.net/articles/axis2/java/2006/09/13/working-with-axis2">http://www.wso2.net/articles/axis2/java/2006/09/13/working-with-axis2</a></p>
<p>Apache Tomcat-<a
href="http://tomcat.apache.org/">http://tomcat.apache.org</a></p>
<p>Spring Framework-<a
href="http://www.springframework.org/">http://www.springframework.org/</a></p>
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