Android - 從服務器獲取響應時驗證JSON以避免出現JSONException

Question

在我的一些與服務器通信並使用http獲取響應的應用程序中，我使用json格式化數據服務器端以及當它到達設備我使用類似於我在代碼中找到的代碼：

private class LoadData extends AsyncTask<Void, Void, String> 
{ 
private JSONArray jArray; 
private String result = null; 
private InputStream is = null; 
private String entered_food_name=choice.getText().toString().trim(); 
protected void onPreExecute() 
{ 
} 

@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/food.php"); 
nameValuePairs.add(new BasicNameValuePair("Name",entered_food_name)); 
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs,"UTF-8")); 
HttpResponse response = httpclient.execute(httppost); 

HttpEntity entity = response.getEntity(); 
is = entity.getContent(); 

    //convert response to string 

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 = result.replace('\"', '\'').trim(); 

} 
catch(Exception e){ 
    Log.e("log_tag", " connection" + e.toString());      
} 


return result; 

} 

@Override 
protected void onPostExecute(String result) 
{ 
try{ 

    String foodName=""; 
    int Description=0; 

    jArray = new JSONArray(result); // here if the result is null an exeption will occur 
    JSONObject json_data = null; 

    for (int i = 0; i < jArray.length(); i++) { 
     json_data = jArray.getJSONObject(i); 
     foodName=json_data.getString("Name"); 
     . 
     . 
     . 
     . 
     . 
    } 
    catch(JSONException e){ 
     **// what i can do here to prevent my app from crash and 
     // make toast " the entered food isnot available " ????** 
     Log.e("log_tag", "parssing error " + e.toString()); 
    } 
} 
} 

我試圖在我找到此代碼的頁面上使用該解決方案。繼承人的方式鏈接How do I prevent my app from crashing unexpectedly, "force close", when using JSON data, and handle the exception instead?

我試着檢查我的JSON響應與在線驗證和JSON返回是有效的。我認爲，當用戶處於較差的覆蓋區域時，連接暫時中斷或者導致json被破壞，從而導致json異常，即使我嘗試了在該鏈接中發佈的線程中建議的方法。所以我希望能夠驗證JSON到手機的時候，所以如果它的有效的我可以繼續，如果不是，我想嘗試修復它，或者至少不要嘗試通過一個破碎的格式不正確的JSON數組放入導致JSONException的其中一個方法中。

驗證字符串的任何提示我在響應中獲取以確保其有效的JSON會很棒。

編輯：有關問題的補充堆棧轉儲

org.json.JSONException: Value null at results of type org.json.JSONObject$1 cannot be  converted to JSONArray 
at org.json.JSON.typeMismatch(JSON.java:96) 
at org.json.JSONObject.getJSONArray(JSONObject.java:548) 
at it.cores.Activity$GetM.doInBackground(Activity.java:1159) 
at it.cores.Activity$GetM.doInBackground(Activity.java:1) 
at android.os.AsyncTask$2.call(AsyncTask.java:185) 
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306) 
at java.util.concurrent.FutureTask.run(FutureTask.java:138) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581) 
at java.lang.Thread.run(Thread.java:1019) 

Answer 1

你必須確保你做一個空檢查/或任何其他驗證如檢查後做了解析，如果它包含做任何操作之前響應代碼在String結果上。

protected void onPostExecute(String result) 
{ 
try{ 

    String foodName=""; 
    int Description=0; 

if(result!=null)//Do your validation for result 

{ 
    jArray = new JSONArray(result); // here if the result is null an exeption will occur 
    JSONObject json_data = null; 

    for (int i = 0; i < jArray.length(); i++) { 
     json_data = jArray.getJSONObject(i); 
     foodName=json_data.getString("Name"); 
     . 
     . 
     . 
     . 
     . 
    } 
} 
    catch(JSONException e){ 
     **// what i can do here to prevent my app from crash and 
     // make toast " the entered food isnot available " ????** 
     Log.e("log_tag", "parssing error " + e.toString()); 
    } 
}