public COMPONENT getComponent(ComponentId id) {
        return componentsById.get(id);
    }
See getComponent(ComponentSpecification)
@param  componentSpecification a component specification string, see {@link com.yahoo.component.Version}
@return the component or null if no component of this name (and version, if specified) is registered here
component/src/main/java/com/yahoo/component/provider/ComponentRegistry.java