Single Interface Single Implementation

This is a very common use case that you have an interface and during runtime, you want to inject one and only one instance of implementation.

Let’s say here is an interface.

public interface A {
    String a();
}

And we have an implementation like this.

public class AImpl implements A {
    @Override
    public String a() {
        return "a real";
    }
}

Now we need to put service.yml in src/main/resources/config folder.

singletons:
- com.networknt.service.A:
  - com.networknt.service.AImpl

This is a configuration file that binds com.networknt.service.AImpl implementation to com.networknt.service.A interface.

Let’s see how to use it in a test case.

    @Test
    public void testGetSingleBean() {
        A a = SingletonServiceFactory.getBean(A.class);
        Assert.assertEquals("a real", a.a());
    }