解析 JSONException：JSONArray 文本必须以字符 1 处的 '[' 开头

我正在尝试将 Android 应用程序与本地 MySQL 数据库连接，但遇到问题 解析 JSON 数组。 （我在这里阅读了所有类似的问题，但没有任何作用。）

错误消息：

Error parsing data org.json.JSONException: A JSONArray text must start with '[' at character 1 of [{"UserName":"Admin","Password":"111","Role":"0"},{"UserName":"Employee","Password":"123","Role":"1"}] 

这是代码：

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    new Connect().execute();
}

private class Connect extends AsyncTask<Void, Void, String> {
    private String result = "";
    private InputStream is = null;
    private ProgressBar progress_Bar;

    protected void onPreExecute() {
        progress_Bar = ((ProgressBar) findViewById(R.id.progress));
        progress_Bar.setVisibility(0);
    }

    @Override
    protected String doInBackground(Void... params) {
        try {
            ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost("http://10.0.2.2/users.php");
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();
        } catch (Exception e) {
            Log.e("log_tag", "Error in http connection " + e.toString());
        }

        // convert response to string
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "utf-8"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
            is.close();
            result = sb.toString();
            result.trim();

        } catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
        }

        return result;
    }

    protected void onPostExecute(String result) {
        String name;

        try {
            Log.d("RESULT", result);

            JSONArray jArray = new JSONArray(result);
            JSONObject json_data = null;
            for (int i = 0; i < jArray.length(); i++) {
                json_data = jArray.getJSONObject(i);

                Toast.makeText(getApplicationContext(), "", Toast.LENGTH_LONG).show();
            }
        } catch (JSONException e) {
            Log.e("log_tag", "Error parsing data " + e.toString());
        }
    }
}

这是 PHP 代码：

<?php
$con1=mysql_connect("localhost", "root", "");

mysql_select_db("sehaty");
mysql_query("SET NAMES utf8"); 

$sql = mysql_query("SELECT * FROM users");
while($row = mysql_fetch_assoc($sql)) {
    $output[]=$row;
}
$data = json_encode($output);
print($data);
mysql_close();
?>

也许您的数据无效，因为存在前导/尾随空格/换行符/...

我会预处理result in onPostExcecute(...)像这样：

private final static String TAG = "YourApplication";

public static String asHex(String str)
{
    byte[] buf = str.getBytes();
    final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
    char[] chars = new char[2 * buf.length];
    for (int i = 0; i < buf.length; ++i)
    {
        chars[2 * i] = HEX_CHARS[(buf[i] & 0xF0) >>> 4];
        chars[2 * i + 1] = HEX_CHARS[buf[i] & 0x0F];
    }
    return new String(chars);
}

protected void onPostExecute(String result) {
    try {
        result = result.replaceAll("[\n\t]", "").replaceAll("[^ A-Za-z0-9\",\[\]{}]", "").trim();
        Log.d(TAG, "RESULT: #" + result + "#");
        Log.d(TAG, "RESULT: " + asHex(result));

        JSONArray jArray = new JSONArray(result);
        for (int i = 0; i < jArray.length(); i++) {
            Log.d(TAG, "USERS: " + jArray.getJSONObject(i).toString());
        }
    } catch (JSONException e) {
        Log.e(TAG, "ERROR: " + e.toString());
    }
}