82

Designing a Service's Interaction Layer

}

}

Code Example 3.10

Implementation of a Service Specific Exception

Code Example 3.11 shows the service implementation for the same weather

service interface. This example illustrates how the service might throw

CityNotFoundException

.

public class WeatherServiceImpl implements WeatherService {

public String getWeather(String city)

throws CityNotFoundException {

if(!validCity(city))

throw new CityNotFoundException(city + " not found");

// Get weather info and return it back

}

}

Code Example 3.11

Example of a Service Throwing a Service Specific Exception

Chapter 5 describes the details of handling exceptions on the client side. (In

particular, refer to  Handling Exceptions  on page 230.) On the service side, keep

in mind how to include exceptions in the service interface and how to throw them.

Generally, you want to do the following:

E

Convert application specific errors and other Java exceptions into meaningful 

service specific exceptions and throw these service specific exceptions to the 

clients.

Although they promote interoperability among heterogeneous platforms, Web

service standards cannot address every type of exception thrown by different plat 

forms. For example, the standards do not specify how Java exceptions such as

java.io.IOException

 and 

javax.ejb.EJBException

 should be returned to the

client. As a consequence, it is important for a Web service from the service's

interoperability point of view to not expose Java specific exceptions (such as

those just mentioned) in the Web service interface. Instead, throw a service spe 

cific exception. In addition, keep the following points in mind: