a cup of java

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.

In one of my previous posts I mentioned about building a JAR using ANT.  This post – building a WAR (Web Application Archive) – is just an add-on to that.

Structure of a WAR file

Application.war
|-- META-INF
|  |-- manifest.mf
|-- WEB-INF
|  |-- web.xml   - deployment descriptor
|  |-- classes   - class files organized in packages
|  |-- lib       - other libraries
|
|-- <other files, directories etc.>

Deployment descriptor
This is a sample deployment descriptor from Java Servlet Specification version 2.4. Get the descriptor (.pdf)


Build file

<project name="my.enterprise.project" default="build.my.war">
<property name="deploy.dir" value="/my/deploy/dir" />
<property name="file.name" value="Application.war" />
  <target name="build.my.war">
    <fileset dir="contents">
      <include name="**/*"/>
    </fileset>
    <war destfile="${file.name}" webxml="conf/web.xml">
      <classes dir="bin" />
    </war>
    <echo>Copying ${file.name}...</echo>
    <copy file="${file.name}" todir="${deploy.dir}" />
    <delete file="${file.name}" />
  </target>
</project>

The above build file assumes that all the non-java resources and JSPs are within the “contents” directory. The build file will pick the class files from the “bin” directory within the base. Here the build file is not compiling existing source files. To compile Java files there is another ANT task -  javac.

<javac srcdir="src" destdir="bin" classpathref="application.classpath"/>

Add the javac task before the war task in the build file.

Defining the class path

<path id="application.classpath">
   <fileset dir="/path/to/my/lib">
      <include name="javax.servlet.jar"/>
   </fileset>
</path>

Define the path before the target – build.my.war.

Read more
http://ant.apache.org/manual/CoreTasks/war.html
http://ant.apache.org/manual/CoreTasks/javac.html
http://ant.apache.org/manual/dirtasks.html

An “executable JAR” is nothing but a JAR in which the entry point of execution is defined. That definition can be given in its manifest file (META-INF/Manifest.mf).

The general structure of a JAR file:

+-MyJar.jar
|-+-META-INF
|-|----Manifest.mf
|-+-com
|-|-+-package
|-|-|----MyJavaFile.java
|-|-|----MySecondJavaFile.java

The manifest file should contain the details of the JAR file. It keeps the attribute as key-value pairs.

The structure of a manifest file:

Main-Class: com.package.MyJavaFile
Specification-Title: "My Classes"
Specification-Version: "1.0"
Specification-Vendor: "Sun Microsystems, Inc."
Implementation-Title: "subin.util"
Implementation-Version: "build01"
Implementation-Vendor: "Sun Microsystems, Inc."

If the executable JAR is dependent on any other JAR, we need to specify it in the Manifest itself (even though there is an option to do it while invoking the application thru java -cp).

Class-Path: aJar.jar anotherJar.jar

I had some problems in building a JAR file using the conventional jar -cvf command. Whatever I do, it was not picking my custom manifest (I’m very bad). So, I used ANT to build a JAR.

ANT file to build a JAR:

<project name="Demo" default="build.jar.file">
  <target name="build.jar.file">
    <jar destfile="myJar.jar" basedir=".">
      <manifest>
        <attribute name="Main-Class" value="com.package.MyJavaFile" />
        <attribute name="Class-Path" value="aJar.jar anotherJar.jar" />
      </manifest>
    </jar>
    <copyfile dest="/path/to/deploy" src="myJar.jar"/>
  </target>
</project>

* use ANT or Eclipse IDE to build the JAR

Running the JAR from the command-line:

$ java -jar myJar.jar [optional parameters]

External Links:
http://en.wikipedia.org/wiki/Manifest_file
http://en.wikipedia.org/wiki/JAR_file
http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html
http://java.sun.com/docs/books/tutorial/deployment/jar/ – Packaging tutorial from Sun
http://ant.apache.org/manual/
http://en.wikipedia.org/wiki/Apache_Ant