PHP LogCat:String中的JSON无法转换为JSONObject

我正在尝试使用PHP从mySQL数据库获取数据。这是我第一次真正尝试远程获取数据；使用JSON。php文件运行正常，因为它在浏览器中以JSON字符串的形式输出，并且我使用JSONLint对其进行了赋值。所以，我不确定我在这里做错了什么。如有任何帮助，将不胜感激

这就是LogCat抛出的：

Error parsing data org.json.JSONException: Value <?xml of type java.lang.String cannot be converted to JSONObject
threadid=9: thread exiting with uncaught exception (group=0x401dce20)
FATAL EXCEPTION: Thread-10
java.lang.NullPointerException
at com.andaero.test.JSON.JSONMain$1.run(JSONMain.java:39)
at java.lang.Thread.run(Thread.java:1020)

UPDATE：我根据Mark的请求从php文件中删除了echo方法。我认为这与"JSONArray a=json.getJSONArray（"regulatory"）有关。我也尝试了其他人的方法，但没有成功。

以下是类别：

public class JSONfunctions {
    public static JSONObject getJSONfromURL(String url) {
        InputStream is = null;
        String result = "regulatory";
        JSONObject jArray = null;
        // http post
        try {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost(url);
            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, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "'n");
            }
            is.close();
            result = sb.toString();
        } catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
        }
        try {
            jArray = new JSONObject(result);
        } catch (JSONException e) {
            Log.e("log_tag", "Error parsing data " + e.toString());
        }
        return jArray;
    }
}

列表活动：

public class JSONMain extends ListActivity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.listview);
        final ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
        new Thread(new Runnable() {
            public void run() {
                JSONObject json = JSONfunctions
                        .getJSONfromURL("http://192.168.1.34/andaero/regulatory_list_ASC.php");
                try {
                    JSONArray a = json.getJSONArray("regulatory");
                    for (int i = 0; i < a.length(); i++) {
                        HashMap<String, String> map = new HashMap<String, String>();
                        JSONObject e = a.getJSONObject(i);
                        map.put("id", String.valueOf(i));
                        map.put("label", e.getString("label"));
                        map.put("title", e.getString("title"));
                        map.put("caption", e.getString("description"));
                        map.put("dummy", e.getString("gotoURL"));
                        mylist.add(map);
                    }
                } catch (JSONException e) {
                    Log.e("log_tag", "Error parsing data " + e.toString());
                }
            }
        }).start();
        ListAdapter adapter = new SimpleAdapter(this, mylist,
                R.layout.list_item, new String[] { "label", "title", "caption",
                        "dummy" }, new int[] { R.id.label, R.id.listTitle,
                        R.id.caption, R.id.dummy });
        setListAdapter(adapter);
        final ListView lv = getListView();
        lv.setTextFilterEnabled(true);
        lv.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                @SuppressWarnings("unchecked")
                HashMap<String, String> o = (HashMap<String, String>) lv
                        .getItemAtPosition(position);
                Toast.makeText(JSONMain.this,
                        "ID '" + o.get("id") + "' was clicked.",
                        Toast.LENGTH_SHORT).show();
            }
        });
    }
} 

编辑：PHP：

    <?php
//MySQL Database Connect
include 'andaerologin.php';
mysql_select_db("andaero");
$sql=mysql_query("select * from regulatory_list");
$output = new stdClass();
$output->regulatory = array();
while($row = mysql_fetch_assoc($sql)) {
    $output->regulatory[] = $row;
}
header('Cache-Control: no-cache, must-revalidate');
header('Content-type: application/json');
echo (json_encode($output));
mysql_close();
?>

JSON返回的数据**（部分-数据是机密的，JSON已根据上述内容进行了验证！！）

[
{
_id: "**",
label: "**",
title: "**",
description: "**",
date: "**",
gotoURL: null,
intent: "QueryDisplay"
}, * additional rows.....>
]
}