A simple way to prevent running of multiple instances of your application is to use Socket communication. For example, in Groovy the first thing you would execute is something like this: [code] try { // choose a unique port (!!) new Socket('localhost', 1337) ...

Sometimes we may have more than one implementation and/or instance of a service to which we need to route requests. Routing may be controlled by a number of different factors, such as the request type, request arguments, runtime configuration, etc. An implementation of such routing might look something like this: [java] public interface ...

Typically object caching in Java is managed by the container or framework in use. Occasionally however there is a need to manually cache domain-specific objects, whereby a java.util.Map implementation will not suffice. Using the popular ehcache framework as an example, the following pattern is typically observed: [java] public class SomeClass { private ...

In OSGi using a publisher/subscriber design can be somewhat more complicated that traditional Java environments: [java] public class SomeBundleActivator implements BundleActivator { private SomeService service = ... private ServiceRegistration registration; public void start(BundleContext context) { registration = context.registerService(SomeService.class.getName(), service, null); } ... } public class AnotherBundleActivator ...

The Service Locator pattern is a well-established mechanism for accessing local and remote services in a consistent manner: [java] public interface ServiceLocator { <T> T findService(String serviceName) throws ServiceNotAvailableException; } [/java] Using a structured service name interface we can improve uniformity and reduce the potential for typos: [java] public enum ServiceName { SomeService("SomeService"); ...