HelloController.java

@RestController
public class HelloController {

    @Autowired
    private RestTemplate restTemplate;

    @RequestMapping(value = "/hello")
    public String hello() {
        return "Hello from Spring Boot!";
    }

    @RequestMapping("/chaining")
    public String chaining(@RequestHeader HttpHeaders headers) {
        HttpHeaders tracingHeaders = new HttpHeaders();
        extractHeader(headers, tracingHeaders, "x-request-id");
        extractHeader(headers, tracingHeaders, "x-b3-traceid");
        extractHeader(headers, tracingHeaders, "x-b3-spanid");
        extractHeader(headers, tracingHeaders, "x-b3-parentspanid");
        extractHeader(headers, tracingHeaders, "x-b3-sampled");
        extractHeader(headers, tracingHeaders, "x-b3-flags");
        extractHeader(headers, tracingHeaders, "x-ot-span-context");
        
        ResponseEntity<String> response = restTemplate
            .exchange("http://spring-boot:8080/hello", HttpMethod.GET, new HttpEntity<>(tracingHeaders), String.class);

        return "Chaining + " + response.getBody();
    }

    private static void extractHeader(HttpHeaders headers, HttpHeaders extracted, String key) {
        List<String> vals = headers.get(key);
        if (vals != null && !vals.isEmpty()) {
            extracted.put(key, Arrays.asList(vals.get(0)));
        }
    }
}