在Android下curl（工作）与HttpURLConnection（失败）

Question

我正在尝试将curl调用转换为Http，但是无论我使用什么选项，响应代码始终为400。这是相关的代码段。如果人们能指出我在这里缺少的内容，将不胜感激：

// Java side    
url = new URL(myUrl);
urlConnection = (HttpURLConnection) url.openConnection();

urlConnection.setRequestProperty("Accept", "application/json");
urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
urlConnection.setRequestProperty("Connection", "Keep-Alive");  
urlConnection.setRequestProperty("Charset", "UTF-8");
urlConnection.setRequestProperty("Accept", "*/*");
urlConnection.setRequestMethod("POST");
urlConnection.setDoOutput(true);
urlConnection.setDoInput(true);
urlConnection.connect();

DataOutputStream writer = new 
DataOutputStream(urlConnection.getOutputStream());
writer.writeBytes(buf);
writer.flush();
writer.close();

int responseCode = urlConnection.getResponseCode();
Log.w(TAG, "responseCode = " +responseCode);   // Always 400

// Native side
curl_easy_setopt(curl, CURLOPT_URL, myUrl);
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, buf);

curl_mem_t apiTokenKey;
memset(&apiTokenKey, 0, sizeof(curl_mem_t));
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_mem_callback);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *) &apiTokenKey);

rc = curl_easy_perform(curl);
printf("rc = %d\n", rc); // Always 0