Android中如何使用HttpURLConnection实现一个文件上传

public static String uploadFile(String uploadUrl, String filePath) {    Log.v(TAG, "url:" + uploadUrl);    Log.v(TAG, "filePath:" + filePath);    String nextLine = "\r\n";    String dividerStart = "--";    String boundary = "******";    try {      URL url = new URL(uploadUrl);      HttpURLConnection connection = (HttpURLConnection) url.openConnection();      connection.setChunkedStreamingMode(1024 * 256);      connection.setDoInput(true);      connection.setDoOutput(true);      connection.setUseCaches(false);      connection.setRequestMethod("POST");      // 设置Http请求头      connection.setRequestProperty("Connection", "Keep-Alive");      connection.setRequestProperty("Charset", "UTF-8");      //必须在Content-Type 请求头中指定分界符      connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);      //定义数据写入流，准备上传文件      DataOutputStream dos = new DataOutputStream(connection.getOutputStream());      dos.writeBytes(dividerStart + boundary + nextLine);      //设置与上传文件相关的信息      dos.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\""          + filePath.substring(filePath.lastIndexOf("/") + 1) + "\"" + nextLine);      dos.writeBytes(nextLine);      FileInputStream fis = new FileInputStream(filePath);      byte[] buffer = new byte[1024 * 32];      int count;      // 读取文件内容，并写入OutputStream对象      while ((count = fis.read(buffer)) != -1) {        dos.write(buffer, 0, count);      }      fis.close();      dos.writeBytes(nextLine);      dos.writeBytes(dividerStart + boundary + dividerStart + nextLine);      dos.flush();      // 开始读取从服务器传过来的信息      InputStream is = connection.getInputStream();      BufferedReader br = new BufferedReader(new InputStreamReader(is, "UTF-8"));      String result = br.readLine();      dos.close();      is.close();      connection.disconnect();      return result;    } catch (IOException e) {      e.printStackTrace();    }    return null;}