安卓HttpurlConnection使用BufferedReader读取数据，但在将数据追加到StringBuilder后得到空值

try {
    // 创建URL对象
    URL url = new URL("http://example.com/api/data");

    // 打开连接
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();

    // 设置请求方法
    connection.setRequestMethod("GET");

    // 获取输入流
    InputStream inputStream = connection.getInputStream();

    // 创建BufferedReader对象
    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

    // 创建StringBuilder对象
    StringBuilder stringBuilder = new StringBuilder();

    // 读取数据
    String line;
    while ((line = reader.readLine()) != null) {
        stringBuilder.append(line);
    }

    // 关闭连接和输入流
    reader.close();
    connection.disconnect();

    // 获取读取的数据
    String responseData = stringBuilder.toString();

    // 处理数据
    // ...

} catch (IOException e) {
    e.printStackTrace();
}