May 27, 2021 Design mode
Service Locator Pattern is used when we want to target various services using JNDI queries. G iven the high cost of finding JNDI for a service, the service locator pattern takes full advantage of caching technology. W hen a service is first requested, the service locator looks for the service in JNDI and caches the service object. W hen the same service is requested again, the service locator looks in its cache, which can greatly improve the performance of the application. The following are the entities of this design pattern.
We'll create ServiceLocator, InitialContext, Cache, service as various objects that represent entities. Service1 and Service2 represent entity services.
ServiceLocatorPatternDemo, our demo class here is as a client that will use ServiceLocator to demonstrate the service locator design pattern.
Create a service interface service.
Service.java
public interface Service { public String getName(); public void execute(); }
Create an entity service.
Service1.java
public class Service1 implements Service { public void execute(){ System.out.println("Executing Service1"); } @Override public String getName() { return "Service1"; } }
Service2.java
public class Service2 implements Service { public void execute(){ System.out.println("Executing Service2"); } @Override public String getName() { return "Service2"; } }
Create InitialContext for JNDI queries.
InitialContext.java
public class InitialContext { public Object lookup(String jndiName){ if(jndiName.equalsIgnoreCase("SERVICE1")){ System.out.println("Looking up and creating a new Service1 object"); return new Service1(); }else if (jndiName.equalsIgnoreCase("SERVICE2")){ System.out.println("Looking up and creating a new Service2 object"); return new Service2(); } return null; } }
Create a cache Cache.
Cache.java
import java.util.ArrayList; import java.util.List; public class Cache { private List<Service> services; public Cache(){ services = new ArrayList<Service>(); } public Service getService(String serviceName){ for (Service service : services) { if(service.getName().equalsIgnoreCase(serviceName)){ System.out.println("Returning cached "+serviceName+" object"); return service; } } return null; } public void addService(Service newService){ boolean exists = false; for (Service service : services) { if(service.getName().equalsIgnoreCase(newService.getName())){ exists = true; } } if(!exists){ services.add(newService); } } }
Create a service locator.
ServiceLocator.java
public class ServiceLocator { private static Cache cache; static { cache = new Cache(); } public static Service getService(String jndiName){ Service service = cache.getService(jndiName); if(service != null){ return service; } InitialContext context = new InitialContext(); Service service1 = (Service)context.lookup(jndiName); cache.addService(service1); return service1; } }
Use ServiceLocator to demonstrate the service locator design pattern.
ServiceLocatorPatternDemo.java
public class ServiceLocatorPatternDemo { public static void main(String[] args) { Service service = ServiceLocator.getService("Service1"); service.execute(); service = ServiceLocator.getService("Service2"); service.execute(); service = ServiceLocator.getService("Service1"); service.execute(); service = ServiceLocator.getService("Service2"); service.execute(); } }
Verify the output.
Looking up and creating a new Service1 object Executing Service1 Looking up and creating a new Service2 object Executing Service2 Returning cached Service1 object Executing Service1 Returning cached Service2 object Executing Service2