How does feign obtain header data for the requested interface

Question

I am requesting an interface with feign and need to get the Headers value for that interface.

I have used feign for the requested interface headers transfer parameters before, pass token to headers:

@RequestMapping(method = RequestMethod.GET, value = "/api/get-store-list")
List<Store> getStoreList(@RequestHeader("Authorization") String Authorization);

However, this interface puts the amount of data in the x-total-count of headers, so I still need to get the value of x-total-count. How do I get the value of x-total-count.

Answer 1

Feign has the headers in the Response object, and that can be the return value:

public interface Swapi {
    @RequestLine("GET /people/{id}/")
    Response personResponse(@Param("id") int person);
}

Now you can call headers() on the result. That, of course, leaves you with the body as a string, which is not pretty. Let’s try something more Feign like.

---

@Data
public class Person {
    String name;
    int height;
    int mass;
}

public interface Swapi {
    @RequestLine("GET /people/{id}/")
    Person person(@Param("id") int person);
}

Now the headers are hidden again, but they are still available to the decoder, which is the place that I will plug in:

@RequiredArgsConstructor
public class HeaderReadingDecoder implements Decoder {

    private final Decoder wrappedDecoder;

    @Override
    public Object decode(Response response, Type type) throws IOException {
        var server = response.headers().getOrDefault("server",
            List.of("")).iterator().next();
        System.out.println("server = " + server);
        var etag = response.headers().getOrDefault("etag",
            List.of("")).iterator().next();
        System.out.println("etag = " + etag);
        return wrappedDecoder.decode(response, type);
    }
}

Of course, System.out is evil, but I really don’t know yet what you want to do with that header value. It’s up to you. Now you can use this with:

Swapi swapi = Feign.builder()
    .decoder(new HeaderReadingDecoder(new JacksonDecoder()))
    .target(Swapi.class, "https://swapi.co/api");
Person person = swapi.person(2);
System.out.println("person = " + person);

And you will get:

server = cloudflare
etag = "3a58f420395ff0deed943e331d3bf74b"
person = Person(name=C-3PO, height=167, mass=75)