为什么将 C# HTTP 请求转换为 Java 不起作用？

Question

I am trying to use the Microsoft Custom Vision ^{know more} . I need to make an HTTP request to send the image to be analyzed. I successfully made a request from C# so I know the information is correct.

However, when I tried to make the same request in Java I received an HTTP 400 error.

I believe I did not handle the request correctly in Java. Is that true?

Following are the snippets.

C#:

var client = new HttpClient();
client.DefaultRequestHeaders.Add("Prediction-Key", PredicitionKey);
using (var content = new 
ByteArrayContent(byteData))
{
  content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
  response = await client.PostAsync(url, content);
  Console.WriteLine(await response.Content.ReadAsStringAsync());
}

Java:

HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestProperty("Prediction-Key", predicitionKey);
connection.setRequestProperty("Content-Type", "application/octet-stream");
connection.setDoInput(true);
connection.setDoOutput(true);
connection.getOutputStream().write(data.getData());
connection.connect();

Reader in = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));

Answer 1

First, replace

connection.connect();

with

connection.getResponseCode();

If it still doesn't work, then the headers are the problem.

Since C# code runs successfully

The only difference between your C# request and Java one in fiddler is that Java request has two additional headers (Accept, User-Agent).

Try setting them explicitly

connection.setRequestProperty("Accept", "*/*");
connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36");

If still doesn't work, try removing these two headers or check data you're sending in request body.