org.json.JSONException：org.json.JSONArray类型的Value []无法转换为JSONObject

Question

{"college1":{"data":[{"id":"1","name":"nithin","location":"kannur s","time":"2016-06-20 12:06:30"},{"id":"2","name":"riy","location":"sdsdvxc","time":"2016-06-20 12:49:52"},{"id":"3","name":"royop","location":"kjpooj","time":"2016-06-20 06:15:36"},{"id":"4","name":"butr","location":"kjpooj","time":"2016-06-20 06:16:52"},17:17:03"}],"last_date":["2016-06-20 18:18:15"]}}
json数据

 try
    {
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();

        nameValuePairs.add(new BasicNameValuePair("lasttime",lasttime));

        HttpClient httpClient = new DefaultHttpClient();
        HttpPost post = new HttpPost(ip);
        post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
        HttpResponse response = httpClient.execute(post);
        HttpEntity entity = response.getEntity();
        InputStream is = entity.getContent();
        String result="";
        if(is !=null)
        {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();

            while((line = reader.readLine()) != null)
            {

                sb.append(line + "\n");

            }
            result = sb.toString();
            is.close();

我正在尝试开发与android和wamp的通信。当试图将sqlite日期发送到mysql数据库时。它显示此错误消息。这是我的网络服务。

    $latest = '';
    $datetime=mysql_query("SELECT MAX(time) AS latest from college1");
    while ($row = mysql_fetch_assoc($datetime)) 
    {
        $latest = $row['latest'];           
    }

    if(isset($_POST['lasttime']))
    {
       $dates=$_POST['lasttime'];

       $datetime=mysql_query("SELECT * from college1  WHERE time > '{$dates}'");
       while ($row = mysql_fetch_assoc($datetime)) 
       {
          //print_r($row);
          //$array1[] = $row;
          $retArr['college1']['data'][] = $row;
          $retArr[$row['id']] = $row;
          $retArr[$row['id']]['latest'] = $latest;
       }
       $retArr = json_encode($retArr);
       echo $retArr;
       //echo($retArr);
     }
     mysql_close($con);
?>

org.json.JSONException：org.json.JSONArray类型的Value []无法转换为JSONObject。 将数据传递给服务器并将其作为空值

时显示此错误