80

Designing a Service's Interaction Layer

a 

WeatherService

 interface associated with the WSDL in Code Example 3.7

might invoke the service as shown in Code Example 3.8.

...

Context ic = new InitialContext();

WeatherWebService weatherSvc = (WeatherWebService)

ic.lookup("java:comp/env/service/WeatherService");

WeatherServiceIntf port = (WeatherServiceIntf)

weatherSvc.getPort(WeatherServiceIntf.class);

String returnValue = port.getWeatherByCity("San Francisco");

...

Code Example 3.8

Using Weather Service with WSDL to Java Approach

3.4.1.5

Handling Exceptions

Just like any Java or J2EE application, a Web service application may encounter an

error condition while processing a client request. A Web service application needs to

properly catch any exceptions thrown by an error condition and propagate these

exceptions. For a Java application running in a single virtual machine, you can prop 

agate exceptions up the call stack until reaching a method with an exception handler

that handles the type of exception thrown. To put it another way, for non Web

service J2EE and Java applications, you may continue to throw exceptions up the

call stack, passing along the entire stack trace, until reaching a method with an

exception handler that handles the type of exception thrown. You can also write

exceptions that extend or inherit other exceptions. 

However, throwing exceptions in Web service applications has additional

constraints that impact the design of the service endpoint. When considering how

the service endpoint handles error conditions and notifies clients of errors, you

must keep in mind these points:

  Similar to requests and responses, exceptions are also sent back to the client as 

part of the SOAP messages.

  Your Web service application should support clients running on non Java plat 

forms that may not have the same, or even similar, error handling mechanisms 

as the Java exception handling mechanism.