Single Interface Multiple Implementations

This is a use case where you have an interface, and multiple implementations will all be used during runtime. For example, in light-4j framework, we have multiple StartupHookProviders to be loaded during server startup and execute them one by one. Also, all our middleware handlers are wired into the request/response chain the same way.

Let’s say we have this interface.

public interface Processor {
    String process();
}

And we have the following three implementations want to be executed in sequence.

public class ProcessorAImpl implements Processor {
    @Override
    public String process() {
        return "A";
    }
}

public class ProcessorBImpl implements Processor {
    @Override
    public String process() {
        return "B";
    }
}

public class ProcessorCImpl implements Processor {
    @Override
    public String process() {
        return "C";
    }
}

Here is the service.yml configuration.

singletons:
- com.networknt.service.Processor:
  - com.networknt.service.ProcessorAImpl
  - com.networknt.service.ProcessorBImpl
  - com.networknt.service.ProcessorCImpl

And here is the test case to show how to use it.

    @Test
    public void testGetMultipleBean() {
        Processor[] processors = SingletonServiceFactory.getBeans(Processor.class);
        Assert.assertEquals(processors.length, 3);
        Arrays.stream(processors).forEach(processor -> System.out.println(processor.process()));
    }