I feel compelled to share a simple Web Service
program in Java as I see this is quite an old technology that only advanced things are found everywhere - lot of generated code etc.. but the fundamentals are lost in the process...
1.
Create a SOAP-based Web Service
2.
Look at WSDL
3.
Generate Proxies
4.
Create a Web Services client
Pre-requisites:
1.
Eclipse installed with J2EE
support
Not Required:
1.
Any web server as this is pure
Java based
Basics:
The fundamental elements are to create:
1.
An interface
2.
An implementation class
3.
A webservice publisher
Here is the interface Definition:
package com.sai.ws;
import javax.jws.WebService;
import javax.jws.WebMethod;
import javax.jws.soap.SOAPBinding;
import javax.jws.soap.SOAPBinding.Style;
@WebService
Here using annotations, we are declaring
that this is a WebService Interface with SOAPBinding following the simple RPC
style.
Now to the class that implements this
interface:
@WebService(endpointInterface = "com.sai.ws.EchoServer")
public class
EchoServerImpl implements EchoServer{
@Override
public String
echoMessage(String strMsg) {
String capitalizedMsg;
System.out.println("Server:
EchoMessage() invoked...");
System.out.println("Server:
Message> " + strMsg);
capitalizedMsg = strMsg.toUpperCase();
return capitalizedMsg;
}
}
The implementation merely capitalizes the
message and return he same. Note here that the annotation @WebService needs to
declare that this is an implementation of the interface “com.sai.ws.EchoServer”
which is the endpointInterface of the service.
Now we are done. Implemented the Service.
We need to publish this service. We can publish it locally by the following:
public class EchoServerPublisher {
public static void main(String args[]) {
Endpoint.publish("http://localhost:9876/es",new
EchoServerImpl());
}
}
Now, you execute the above java program and
your Webservice is running. Endpoint creates
and publishes an endpoint for the specified implementor object (EchoServerImpl)
at the given address (http://localhost:9876/es).
The necessary server infrastructure will be created and configured by the
JAX-WS internal implementation using some default configuration.
So far, we have created a webservice
interface, implementation and published it.
Now you can view the WSDL generated by
accessing the URL: http://localhost:9876/es?wsdl
This is a verbose WSDL that describes the
message style, the interface consisting of the request-response style, the
bindings of ‘how’ to acess the service and the ‘where’ to access it finally
(the URL).
The various components of the WSDL may be
summarized as follows:
How do you consume this from a client. Let
us write a simple client project named “WebServiceCLientExample”. Create a
class “SimpleServiceClient” in that project.
Here is the method to access the Service
within the client:
public static void main (String args[]) throws Exception{
final URL url = new URL("http://localhost:9876/es");
final QName name = new QName("http://ws.sai.com/", "EchoServerImplService");
final Service service
= Service.create(url, name);
final EchoServer
simple = service.getPort(EchoServer.class);
System.out.println(simple.echoMessage("Hello Everyone!"));
}
As you see, from the client we need to
specify the URL to access the service: http://localhost:9876/es
Then we need to
specify the qualified namespace that consists of two things:
- The URI is the value of the @namespace
attribute in WSDL.
- The local part is the value of the
service[@name] attribute at the bottom of WSDL.
As shown here:
final QName name = new QName("http://ws.sai.com/", "EchoServerImplService");
Then, we create the
service as in:
final Service
service = Service.create(url, name);
Finally get our port:
final EchoServer simple = service.getPort(EchoServer.class);
Then, call the methods on that port:
simple.echoMessage("Hello Everyone!")
This completes a simple webservice and a
client to the webservice in plain java. However, not that for the client to
work in the above format (without any proxy generation), you will have to
include the webservice project in the classpath of the client project. If not, service.getPort(EchoServer.class) will throw an error as EchoServer.class cannot
be found in the path.
So, in reality, you will not have the
server classes available on the client side as Webservices are for remote
access of the service. In that case, you will have to download the WSDL from
the URL http://localhost:9876/es?wsdl
and include into into the client project. Then, right click the file and select
‘Web Services - > Generate Client’. You get this dialog box:
Select only Develop client. If you use the
slider, it will generate a lot more which you can explore if you are interested.
Click ‘next’ and finish.
You will have the following files (proxies
generated)
Now, you should be able to compile the
client and use it remotely.
Hope this helps in your first step to
SOAP-based web services.
