考虑用静态工厂方法替代构造器

public interface Service {

}

//////////////////////////////////////////////////////////////////////////////////////////////////

public interface Provider {
　　Service newService();
}

///////////////////////////////////////////////////////////////////////////////////////////////////

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class Services {

private Services(){}

private static final Map<String,Provider> providers = new ConcurrentHashMap<String,Provider>();

public static final String DEFAULT_PROVIDER_NAME = "<def>";

public static void registerDefaultProvider(Provider p){
　　registerProvider(DEFAULT_PROVIDER_NAME, p);
}

public static void registerProvider(String name, Provider p) {
　　providers.put(name, p);
}

public static Service newInstance() {
　　return newInstance(DEFAULT_PROVIDER_NAME);
}

public static Service newInstance(String name) {
　　Provider p = providers.get(name);
　　if (p == null)
　　　　throw new IllegalArgumentException("No provider register with name: " + name);

　　return p.newService();
}

public static void main(String[] args) {
　　// TODO Auto-generated method stub
　　Service s = newInstance();
　　Service sCustomer = newInstance("customer");
}

}