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;
}