How to read header value from feign Response

Question

i am using spring boot to call a openfeign client and from the Response of that feign i need to extract some header values.how can i do that. can anybody help please. just help me wheather we can do that or not!

Answer 1

Yes, you can do that. With Feign, we usually declare our interface with the method returning our class and Feign will automatically de-serialise the response from JSON into our POJO.

Here is the interface (operation):

@FeignClient(name = "library-book-service")
@RequestMapping("books")
public interface BookClient {

    @GetMapping
    public List<Book> getBooks(
        @RequestParam("page") Optional<Integer> pageNum,
        @RequestParam("size") Optional<Integer> pageSize,
        @RequestParam("reader") Optional<Long> readerId);
}

And then you can use the feign client like this:

@Service
@RequiredArgsConstructor
public class BookService {
    private final @NonNull BookClient bookClient;

    public List<Book> retrieveBooks(
        Optional<Integer> pageNum, 
        Optional<Integer> pageSize, 
        Optional<Long> readerId) {

            return bookClient.getBooks(pageNum, pageSize, readerId);
    }

However, in order to have access to the response headers, you need to declare your methods to return feign.Response.

import feign.Response;

@FeignClient(name = "library-book-service")
@RequestMapping("books")
public interface BookClient {

    @GetMapping
    public Response getBooks(
        @RequestParam("page") Optional<Integer> pageNum,
        @RequestParam("size") Optional<Integer> pageSize,
        @RequestParam("reader") Optional<Long> readerId);
}

This way you can have access to the response body and headers:

@Service
@RequiredArgsConstructor
public class BookService {
    private final @NonNull BookClient bookClient;
    private final @NonNull ObjectMapper objectMapper;

    public List<Book> retrieveBooks(
        Optional<Integer> pageNum, 
        Optional<Integer> pageSize, 
        Optional<Long> readerId) {

          var response = bookClient.getBooks(pageNum, pageSize, readerId);
          if (response == null) {
            return Collections.emptyList();
          }

          // retrieve body
          var books = objectMapper.readValue(
            new BufferedReader(new InputStreamReader(response.body().asInputStream(), StandardCharsets.UTF_8)),
            new TypeReference<List<Book>>(){});

          // retrieve headers
          Map<String, Collection<String>> headers = response.headers();
          // ... do whatever you need with the headers

          return books;
    }

Answer 2

You can use import feign.Response as a response like:

@PostMapping("/test")
Response test(@RequestBody TestRequest testRequest);

then you can reach http header

response.headers().get(HEADER_NAME).toString();

if you want get body in this case you have to some json-string manipulation by use response.body() this page may help you for this