无法理解URLConnection的getInputStream（）

Question

以下是URLConnection

中定义的getInputStream（）代码

public InputStream getInputStream() throws IOException {
        throw new UnknownServiceException("Does not support writing to the input stream");
    }

我正在使用它在我的代码中获取输入流对象

private String makeHttpRequest(URL url) throws IOException {
            String jsonResponse = "";
            HttpURLConnection urlConnection = null;
            InputStream inputStream = null;
            try {
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.setReadTimeout(10000 /* milliseconds */);
                urlConnection.setConnectTimeout(15000 /* milliseconds */);
                urlConnection.connect();
                inputStream = urlConnection.getInputStream();
                jsonResponse = readFromStream(inputStream);
            } catch (IOException e) {
                // TODO: Handle the exception
            } finally {
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
                if (inputStream != null) {
                    // function must handle java.io.IOException here
                    inputStream.close();
                }
            }
            return jsonResponse;
        }

  

inputStream = urlConnection.getInputStream（）;

这个语句是如何工作的，因为在它的定义中它抛出了一个UnknownServiceException（）