Three Ways to Call External APIs in Spring Boot: HttpClient, RestTemplate, and Feign

Spring Boot inherits Spring's strengths while simplifying configuration, and many projects need to call external URLs or third‑party services. This guide presents three methods to achieve that without Dubbo.

1. Method One: Raw HttpClient Request

Use Apache HttpClient to build and send a POST request, set JSON payload, add the Authorization header, and parse the JSON response.

/*
 * @description get方式获取入参，插入数据并发起流程
 * @author lyx
 * @date 2022/8/24 16:05
 * @params documentId
 * @return String
 */
@RequestMapping("/submit/{documentId}")
public String submit1(@PathVariable String documentId) throws ParseException {
    Map<String,Object> map = task2Service.getMap(documentId);
    String jsonStr = JSON.toJSONString(map, SerializerFeature.WRITE_MAP_NULL_FEATURES, SerializerFeature.QuoteFieldNames);
    JSONObject jsonObject = JSON.parseObject(jsonStr);
    JSONObject sr = task2Service.doPost(jsonObject);
    return sr.toString();
}

/*
 * @description 使用原生httpClient调用外部接口
 * @author lyx
 * @date 2022/8/24 16:08
 * @params date
 * @return JSONObject
 */
public static JSONObject doPost(JSONObject date) {
    String assessToken = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzUxMiJ9...";
    CloseableHttpClient client = HttpClients.createDefault();
    String url = "http://39.103.201.110:30661/xdap-open/open/process/v1/submit";
    HttpPost post = new HttpPost(url);
    StringEntity s = new StringEntity(date.toString());
    s.setContentType("application/json");
    s.setContentEncoding("UTF-8");
    post.setEntity(s);
    post.addHeader("Authorization", "Bearer " + assessToken);
    HttpResponse res = client.execute(post);
    if (res.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
        String result = EntityUtils.toString(res.getEntity());
        return JSONObject.parseObject(result);
    }
    throw new RuntimeException("Request failed");
}

2. Method Two: RestTemplate

RestTemplate provides convenient getForObject, getForEntity, postForEntity, postForObject, and postForLocation methods. Examples show how to build URIs, pass parameters, and retrieve responses.

RestTemplate restTemplate = new RestTemplate();
UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://USER-SERVICE/user?name={name}")
    .build()
    .expand("dodo")
    .encode();
URI uri = uriComponents.toUri();
ResponseEntity<String> response = restTemplate.getForEntity(uri, String.class);

3. Method Three: Feign Client

Add the Feign starter dependency, enable Feign with @EnableFeignClients, and define a Feign interface annotated with @FeignClient. Include a custom RequestInterceptor to inject tokens into request headers.

@Configuration
public class FeignConfig implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate requestTemplate) {
        requestTemplate.header("token", "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzUxMiJ9...");
    }
}

@FeignClient(url = "${outSide.url}", name = "service2")
public interface FeignService2 {
    @RequestMapping(value = "/custom/outSide", method = RequestMethod.POST)
    @ResponseBody
    String getMessage(@Valid @RequestBody TestDto testDto);
}

Finally, a controller can autowire the Feign client and expose an endpoint that forwards the request to the external service.

@RestController
public class DemoController {
    @Autowired
    FeignService2 feignService2;

    @PostMapping("/test2")
    public String test2(@RequestBody TestDto testDto) {
        return feignService2.getMessage(testDto);
    }
}