A Web services client is basically a SOAP client. Given a WSDL (Web Services
Definition Language) file, let us see how to generate a stub for the web
service and write a client which access the web service through the stub.
Description
Let us look at how to write a simple Web service client
for a Oracle9iAS J2EE Web service. Our web service has two methods, one
which returns an exchange rate between two currencies and another which
converts currencies. The method definitions that are part of the WSDL for
our discussion is:
Oracle9iAS J2EE Web services infrastructure requires a stub, which will
be used by the client to access the web service. The following listing
shows the stub which encapsulates the actual method calls.
public String endpoint
=
"http://localhost:8888/Workspace2-Project1-context-root/CurrencyConvertor";
private OracleSOAPHTTPConnection m_httpConnection
= null;
// This method encapsulates the invocation
details of the convert method.
public Float convert(String fromCurrency,
String toCurrency, Float amount) throws Exception
{
Float returnVal = null;
URL endpointURL = new URL(endpoint);
Call call = new Call();
call.setSOAPTransport(m_httpConnection);
call.setTargetObjectURI("CurrencyConvertor");
//Preparing to call the method
"convert" on the service call.setMethodName("convert");
call.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC);
//Set up the parameters for
the method Vector params = new Vector();
params.addElement(new Parameter("fromCurrency",
String.class, fromCurrency, null));
params.addElement(new Parameter("toCurrency",
String.class, toCurrency, null));
params.addElement(new Parameter("amount",
Float.class, amount, null));
// Associate the created parameters
with the call object call.setParams(params);
// Invoke the call using the enpointURL
defined above Response response = call.invoke(endpointURL,
""); if (!response.generatedFault())
{
Parameter result = response.getReturnValue();
returnVal = (Float)result.getValue();
}
else
{
Fault fault = response.getFault();
throw new SOAPException(fault.getFaultCode(),
fault.getFaultString());
}
return returnVal;
}
// This method encapsulates the invocation
details of the exchangeRate method
public Float exchangeRate(String from, String
to) throws Exception
{
Float returnVal = null;
URL endpointURL = new URL(endpoint);
Call call = new Call();
call.setSOAPTransport(m_httpConnection);
call.setTargetObjectURI("CurrencyConvertor");
//Preparing to call the method
"exchangeRate" on the service call.setMethodName("exchangeRate");
call.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC);
//Set up the parameters for
the method Vector params = new Vector();
params.addElement(new Parameter("from",
String.class, from, null));
params.addElement(new Parameter("to",
String.class, to, null));
// Associate the created parameters
with the call object call.setParams(params);
// Invoke the call using the enpointURL
defined above Response response = call.invoke(endpointURL,
""); if (!response.generatedFault())
{
Parameter result = response.getReturnValue();
returnVal = (Float)result.getValue();
}
else
{
Fault fault = response.getFault();
throw new SOAPException(fault.getFaultCode(),
fault.getFaultString());
}
return returnVal;
}
...
The complete stub source listing can be found here.
Once the stub is written / generated, clients can instantiate the stub
to invoke the web service. Clients can be any java based clients. For a
client to access the stub, the stub class should be present in the classpath
of the client application. Assuming the name of the generated client as
CurrencyConverterStub.java, it needs to be used as follows
...
CurrencyConverterStub handle = new CurrencyConverterStub();
handle.convert("USD","JPY",new Float(50));
....
The complete listing of a simple client can be found here.
This snippet shows the steps that needs to be followed to develop a
simple web services client and to consume a service. You can find a fully
functional sample here.
Note : Oracle9i JDeveloper makes development of Web services
simpler. It also facilitates the generation of WSDL files, stubs through
a wizard based interface. You can download Oracle9i JDeveloper from here.
Bookmark