Is there an equivalent for Springs Resource in Micronaut?

Question

I am migrating a tiny Spring Boot application to Micronaut 1.0.1 and I was wondering if there is an equivalent for org.springframework.core.io.Resource and their implementation such as ClasspathResource?

In Spring Boot I inject a resource into a service using its constructor.

@Service
public class MyService() {

    private final Resource resource;

    public MyService(Resource resource) { this.resource = resource; }
}

How can I do this in Micronaut?

@Singleton
public class MyService() {

    private final Resource resource;

    @Inject
    public MyService(Resource resource) { this.resource = resource; }
}

score 10 · Accepted Answer · answered Nov 19 '18 at 13:07

In Micronaut you can use io.micronaut.core.io.ResourceLoader variants, such as io.micronaut.core.io.scan.ClassPathResourceLoader or io.micronaut.core.io.file.FileSystemResourceLoader. One option to get them is via io.micronaut.core.io.ResourceResolver:

ClassPathResourceLoader loader = new ResourceResolver().getLoader(ClassPathResourceLoader.class).get();
Optional<URL> resource = loader.getResource("classpath:foo/bar.txt");

score 3 · Answer 2 · answered May 08 '20 at 18:07

I used io.micronaut.core.io.ResourceLoader. Wired through the constructor:

@Controller("root")
public class MyController {

    private final ResourceLoader loader;

    public MyController(ResourceLoader loader) {
        this.loader = loader;
    }

    @Get("/index")
    @Produces(MediaType.TEXT_HTML)
    public String greet() throws IOException {
        return new String(loader.getResourceAsStream("index.html").get().readAllBytes());
    }
}

path to my index.html: src/main/resources/index.html

score 3 · Answer 3 · answered Dec 08 '20 at 21:16

ResourceLoader works well but you can do better. In Micronaut you can use io.micronaut.core.io.Readable. It is roughly equivalent to Spring's Resource. You can also use Readable in ConfigurationProperties and thus bind your configuration yaml/properties directly to Readable properties:

micronaut:
  application:
    name: Demo
images:
  image-file: "classpath:images/bismarckia-nobilis.jpg"
  # image-file: "file:/path/to/images/bismarckia-nobilis.jpg"
  other-files:
    - "classpath:images/bismarckia-nobilis.jpg"
    - "classpath:images/bamboo.jpg"
    - "classpath:images/hibiscus.jpg"

I have created:

Blog post: https://hillert.com/blog/from-resource-to-readable/
Demo: https://github.com/ghillert/resource-readable-demo

score 2 · Answer 4 · answered Jun 03 '22 at 08:26

You can do it this way

@Singleton
public class MyService {

    @Value("classpath:your-file.json")
    private Readable readable;
}

or

@Singleton
public class MyService {

    private final Readable readable;

    public MyService(@Value("classpath:your-file.json") Readable file) {
        this.readable = readable;
    }
}

Is there an equivalent for Springs Resource in Micronaut?

4 Answers4

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