title: setRequestProperty function of HttpURLConnection
body: <p>I achieve the POST request in Android and upload a picture to service successful. </p>
  
  <p>I did not use the setRequestProperty function; But I want to know what the effect about this function is.</p>
  
  <p>This is the code:</p>
  
  <pre><code>URL url = new URL("http://192.168.191.104:8080/myapp/servlet/MyServlet");
  HttpURLConnection connection = ((HttpURLConnection) url
          .openConnection());
  connection.setDoInput(true);
  connection.setDoOutput(true);
  connection.setUseCaches(false);
  connection.setRequestMethod("POST");
  connection.connect();
  OutputStream out = connection.getOutputStream();
  int len;
  byte[] buffer = new byte[1024];
  // 读取文件
  FileInputStream fileInputStream = new FileInputStream(Environment
          .getExternalStorageDirectory().getAbsolutePath() + "/123.jpg");
  while ((len = fileInputStream.read(buffer, 0, 1024)) != -1) {
      out.write(buffer);
  }
  out.flush();
  out.close();
  fileInputStream.close();
  InputStream input = connection.getInputStream();
  while ((len = input.read(buffer)) != -1) {
      Log.i("tag", "data:" + new String(buffer, 0, len));
  }
  input.close();
  connection.disconnect();
  </code></pre>
  
  <p>Could anyone explain the effect of setRequestProperty function in HttpURLConnection?</p>