HTTP 客戶端設計：OkHttp 連接池與多場景應用

@Configuration
public class HttpClientConfig {

@Bean
public OkHttpClient okHttpClient() {
return new OkHttpClient.Builder()
// 連線池設定
.connectionPool(new ConnectionPool(
100, // 最大閒置連線數
5, TimeUnit.MINUTES // 閒置時間
))

// 逾時設定
.connectTimeout(10, TimeUnit.SECONDS)
.readTimeout(30, TimeUnit.SECONDS)
.writeTimeout(30, TimeUnit.SECONDS)

// 重試
.retryOnConnectionFailure(true)

.build();
}
}

@Component
public class HttpClientService {

@Autowired
private OkHttpClient okHttpClient;

/**
* GET 請求
*/
public HttpResult get(String url, Map<String, String> headers) {
Request request = new Request.Builder()
.url(url)
.headers(Headers.of(headers))
.get()
.build();

return execute(request);
}

/**
* POST 請求（JSON）
*/
public HttpResult postJson(String url, Object body, Map<String, String> headers) {
String json = JsonUtil.toJson(body);

Request request = new Request.Builder()
.url(url)
.headers(Headers.of(headers))
.post(RequestBody.create(json, MediaType.parse(“application/json”)))
.build();

return execute(request);
}

/**
* POST 請求（Form）
*/
public HttpResult postForm(String url, Map<String, String> params, Map<String, String> headers) {
FormBody.Builder formBuilder = new FormBody.Builder();
params.forEach(formBuilder::add);

Request request = new Request.Builder()
.url(url)
.headers(Headers.of(headers))
.post(formBuilder.build())
.build();

return execute(request);
}

private HttpResult execute(Request request) {
try (Response response = okHttpClient.newCall(request).execute()) {
return HttpResult.builder()
.statusCode(response.code())
.body(response.body() != null ? response.body().string() : null)
.headers(response.headers().toMultimap())
.success(response.isSuccessful())
.build();

} catch (IOException e) {
return HttpResult.builder()
.success(false)
.errorMessage(e.getMessage())
.build();
}
}
}

@Data
@Builder
public class HttpResult {
private boolean success;
private int statusCode;
private String body;
private Map<String, List<String>> headers;
private String errorMessage;

/**
* 解析 JSON 回應
*/
public <T> T parseJson(Class<T> clazz) {
if (!success || body == null) {
return null;
}
return JsonUtil.fromJson(body, clazz);
}

/**
* 解析 JSON 陣列回應
*/
public <T> List<T> parseJsonList(Class<T> clazz) {
if (!success || body == null) {
return Collections.emptyList();
}
return JsonUtil.fromJsonList(body, clazz);
}
}

@Component
public class TracingHttpClient {

private static final List<String> TRACING_HEADERS = List.of(
“x-request-id”,
“x-b3-traceid”,
“x-b3-spanid”,
“x-b3-parentspanid”,
“x-b3-sampled”
);

@Autowired
private HttpClientService httpClient;

/**
* 從當前請求提取追蹤 Header
*/
public Map<String, String> extractTracingHeaders(HttpServletRequest request) {
Map<String, String> headers = new HashMap<>();

for (String name : TRACING_HEADERS) {
String value = request.getHeader(name);
if (value != null) {
headers.put(name, value);
}
}

return headers;
}

/**
* 發送請求，自動帶入追蹤 Header
*/
public HttpResult getWithTracing(String url, HttpServletRequest currentRequest) {
Map<String, String> headers = extractTracingHeaders(currentRequest);
return httpClient.get(url, headers);
}
}

@Component
public class RetryableHttpClient {

@Autowired
private HttpClientService httpClient;

/**
* 帶重試的請求
*/
public HttpResult getWithRetry(String url, Map<String, String> headers, int maxRetries) {
int attempt = 0;
HttpResult result = null;

while (attempt < maxRetries) {
result = httpClient.get(url, headers);

if (result.isSuccess()) {
return result;
}

// 只對可重試的錯誤重試
if (!isRetryable(result.getStatusCode())) {
break;
}

attempt++;
sleep(calculateBackoff(attempt));
}

return result;
}

private boolean isRetryable(int statusCode) {
// 5xx 錯誤和 429 (Too Many Requests) 可重試
return statusCode >= 500 || statusCode == 429;
}

private long calculateBackoff(int attempt) {
// 指數退避：1秒, 2秒, 4秒…
return (long) Math.pow(2, attempt – 1) * 1000;
}
}

@Service
public class ShopeeApiClient {

@Autowired
private RetryableHttpClient httpClient;

public List<ShopeeOrder> getOrders(String accessToken) {
String url = “https://partner.shopeemobile.com/api/v2/order/get_order_list”;

Map<String, String> headers = Map.of(
“Authorization”, “Bearer “ + accessToken,
“Content-Type”, “application/json”
);

HttpResult result = httpClient.getWithRetry(url, headers, 3);

if (!result.isSuccess()) {
throw new ApiException(“Shopee API 錯誤: “ + result.getErrorMessage());
}

return result.parseJsonList(ShopeeOrder.class);
}
}