94

Designing a Service's Interaction Layer

A Web service such as this can be designed using a service endpoint that

receives the client's request and then delegates the request directly to the service's

appropriate logic in the processing layer. The service's processing layer processes

the request and, when the processing completes, the service endpoint returns the

response to the client. (See Figure 3.6.)

Code Example 3.15 shows the weather service interface performing some

basic parameter validation checks in the interaction layer. The interface also gets

required information and passes that information to the client in a synchronous

manner:

public class WeatherServiceImpl implements 

WeatherService, ServiceLifecycle {

public void init(Object context) throws JAXRPCException {....}

public String getWeather(String city)

throws CityNotFoundException {

/** Validate parameters **/

if(!validCity(city))

throw new CityNotFoundException(....);

/** Get weather info form processing layer and **/

/ **return results **/

return (getWeatherInfoFromDataSource(city));

}

public void destroy() {....}

}

Code Example 3.15

Performing a Synchronous Client Interaction

Now let's examine an asynchronous interaction between a client and a ser 

vice. When making a request for this type of service, the client cannot afford to

wait for the response because of the significant time it takes for the service to

process the request completely. Instead, the client may want to continue with

some other processing. Later, when it receives the response, the client resumes

whatever processing initiated the service request. Typically in these types of ser