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  • Subinkrishna Gopi 3:26 pm on October 13, 2009 Permalink |
    Tags: , , , , , web services,   

    How-to: Write web services using Axis2 (Part 2) 

    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 !!!

     
  • Subinkrishna Gopi 3:45 pm on August 25, 2009 Permalink |
    Tags: , , , , , , web services,   

    How-to: Write web services using Axis2 

    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.

    image

    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 :D. 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.

     
  • Subinkrishna Gopi 2:22 pm on October 18, 2007 Permalink |
    Tags: architecture, , , , soa, , web services   

    Service Oriented Architecture – Basics 

    SOA – Service Oriented Architecture – is an architectural design pattern, where an application is developed as a set of logically & functionally separate and independent services. Each of these services can be implemented in any platform, programming language using any of the available technologies. These services can communicate with each other to fulfill their needs and can send & receive pieces of information from other services as well. One service can interact with more than one service to get the desired things done. SOA can be implemented using web services, since the protocols & standards of internet are very much platform & programming language independent. The main purpose of SOA is to reduce the coupling between the modules.

    Requirements of SOA
    1) We should make use of standards & protocols supported by most of the platforms since these services may be distributed among wide verity of them. (Means, there should be a standard and widely accepted mechanism for the services to talk with each other)
    2) There should be a “clear & unambiguous” service interface syntax.
    3) There should be a service registry mechanism to retrieve the suitable services.

    SOA Building Blocks
    Service provider: Provides a set of services to the requesting clients/services. The provider can restrict the services they offer as well as define the service scope to public or private. Public services can be accessed by anyone over the internet but the private services are restricted to certain clients. The service provider should register the interface & service access information with the service registry.

    Service Broker/Service Registry: Provides the interface & service access information to any service requestors. The implementer can also decide the scope of the registry too.

    Service requestor: It’s a web service client. The requester searches the service registry using different search methods to find a service entry and then binds to the corresponding service provider to get the things done.

    Useful links
    http://en.wikipedia.org/wiki/Service-oriented_architecture
    http://webservices.xml.com/pub/a/ws/2003/09/30/soa.html
    http://www.service-architecture.com/

     
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