SpringBoot External API Calls: HttpClient, RestTemplate, and Feign Integration

SpringBoot inherits Spring's strengths and further simplifies application setup; when a module needs to call external interfaces, three non‑Dubbo methods are available.

1. Raw HttpClient

/*
 * @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 {
    //此处将要发送的数据转换为json格式字符串
    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();
}

The underlying HTTP call can be performed with a plain HttpClient:

/*
 * @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();
    // 要调用的接口url
    String url = "http://39.103.201.110:30661 /xdap-open/open/process/v1/submit";
    HttpPost post = new HttpPost(url);
    JSONObject jsonObject = null;
    try {
        //创建请求体并添加数据
        StringEntity s = new StringEntity(date.toString());
        //此处相当于在header里头添加content-type等参数
        s.setContentType("application/json");
        s.setContentEncoding("UTF-8");
        post.setEntity(s);
        //此处相当于在Authorization里头添加Bearer token参数信息
        post.addHeader("Authorization", "Bearer " + assessToken);
        HttpResponse res = client.execute(post);
        if (res.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
            // 返回json格式：
            String result = EntityUtils.toString(res.getEntity());
            jsonObject = JSONObject.parseObject(result);
        }
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    return jsonObject;
}

2. RestTemplate

RestTemplate offers convenient methods such as getForEntity , getForObject , postForEntity , etc. Example of a GET request using a URI :

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

GET request with URL variables:

RestTemplate restTemplate = new RestTemplate();
Map<String,Object> params = new HashMap<>();
params.put("name", "dada");
ResponseEntity<String> responseEntity = restTemplate.getForEntity("http://USER-SERVICE/user?name={name}", String.class, params);

POST request example (wrapped in a controller method):

@PostMapping("/submit2")
public Object insertFinanceCompensation(@RequestBody JSONObject jsonObject) {
    String documentId = jsonObject.get("documentId").toString();
    return task2Service.submit(documentId);
}

3. Feign

Feign simplifies remote calls. Add the dependency spring-cloud-starter-feign , enable with @EnableFeignClients , and define a client interface:

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

To inject custom headers such as a token, implement a RequestInterceptor :

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

Finally, use the Feign client in a controller to invoke the external service:

@Autowired
FeignService2 feignService2;

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

The article also includes Maven dependency snippets, application entry‑point annotations, and notes on adding request headers for token propagation.