Android的空指針異常？

Question

我是新的android開發人員，我有一個類，我打電話給一個web服務，我越來越json響應，並希望保存在db和hashmap中的這個rsponce，但我得到以下錯誤..

java.lang.NullPointerException 
    at com.hb.hungryhub.DownloadReservations$LoadReservation.doInBackground(DownloadReservations.java:192) 
    At com.hb.hungryhub.DownloadReservations$LoadReservation.doInBackground(DownloadReservations.java:1) 
    at android.os.AsyncTask$2.call(AsyncTask.java:288) 
    at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
    at java.lang.Thread.run(Thread.java:841) 

我的代碼在這裏。

public class DownloadReservations { 

public final static String KEY_RESERVATION_ACTIVE = "active"; 
public final static String KEY_RESERVATION_CREATED_AT = "created_at"; 
public final static String KEY_RESERVATION_DATE = "date"; 
public final static String KEY_RESERVATION_END_TIME = "end_time"; 
public final static String KEY_RESERVATION_ID = "id"; 
public final static String KEY_RESERVATION_NAME = "name"; 
public final static String KEY_RESERVATION_PARTY_SIZE = "party_size"; 
public final static String KEY_RESERVATION_PHONE = "phone"; 
public final static String KEY_RESERVATION_RESTAURANT_ID = "restaurant_id"; 
public final static String KEY_RESERVATION_SPECIAL_REQUEST = "special_request"; 
public final static String KEY_RESERVATION_START_TIME = "start_time"; 
public final static String KEY_RESERVATION_TABLE = "table"; 
public final static String KEY_RESERVATION_UPDATED = "updated_at"; 
public final static String KEY_RESERVATION_USER_ID = "user_id"; 
public final static String KEY_RESERVATION_RESTAURANT_NAME = "rest_name"; 
ConnectionDetector cd; 
AlertDialogManager alert = new AlertDialogManager(); 
private ProgressDialog pDialog; 

DbHelper db;// = new DbHelper(getActivity()); 

JSONParser jParser = new JSONParser();  
ArrayList<HashMap<String, String>> restaurantsList = new ArrayList<HashMap<String, String>>(); 
boolean isParsingCompleted = false; 
Context context; 
JSONArray restaurants = null; 
DownloadReservationListener downloadReservationListener; 
boolean showProcessing = false; 
private static String url_reservation = "http://hungryhub.com:80/api/reservations.json"; 

boolean isUserAuth = true; 
//Users user; 
Restaurants restaurant; 
ArrayList<HashMap<String, String>> bookingList = new ArrayList<HashMap<String, String>>(); 

String email,password, userId; 
DownloadReservations(Context context, DownloadReservationListener downloadReservationListener,String email, String password, boolean showProcessing) { 
    this.context = context; 
    this.downloadReservationListener = downloadReservationListener; 
    this.email = email; 
    this.password = password; 
    this.showProcessing = showProcessing; 
} 

public void startDownloading() { 
    db = new DbHelper(context); 
    beforeSync(); 
} 

public void beforeSync(){ 
    cd = new ConnectionDetector(context); 
    if (!cd.isConnectingToInternet()) { 
     alert.showAlertDialog(context,"Internet Connection Error","Please connect to a working Internet connection",reservationListener,null, false); 
     return; 
    } 
    LoadReservation lr = new LoadReservation(); 
    lr.execute(); 
} 

class LoadReservation extends AsyncTask<String, String, String> { 
    int res_code = -1; 
    String errorMsg = "Cannot get your reservations at this time, please try later."; 
    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 
     if (showProcessing) { 
      pDialog = new ProgressDialog(context); 
      pDialog.setTitle("Processing"); 
      pDialog.setMessage("Please wait..."); 
      pDialog.setIndeterminate(false); 
      pDialog.setCancelable(false); 
      pDialog.show(); 
     } 
    } 

    @Override 
    protected String doInBackground(String... args) { 
     JSONObject obj = new JSONObject(); 
     JSONObject objUser = new JSONObject(); 
     try { 
      objUser.put("email", email); 
      objUser.put("password", password); 

      obj.put("user", objUser); 
      res_code = jParser.postJSONWithUrl(obj,url_reservation); 

      String response = JSONParser.getJson(); 
      if (response.contains("ERR:")) { 
       int startIndex = response.indexOf("ERR:"); 
       if (startIndex > -1) { 
        isUserAuth = false; 
        errorMsg = response.substring(startIndex + "ERR:".length()).trim(); 
        return null; 
       } 
      } 
      String errorMsg = JSONParser.getJson(); 
      if (errorMsg.contains("Incorect login/pass")) { 
       isUserAuth = false; 
       isParsingCompleted = false; 
       return null; 
      } 
      System.out.println(JSONParser.getJson()); 
      JSONArray jarr = new JSONArray(JSONParser.getJson()); 
      System.out.println(jarr.length()); 
      Reservations reservation = new Reservations(); 
     // HashMap<String, String> map = new HashMap<String, String>(); 

      for(int i = 0; i < jarr.length(); i++){ 

       JSONObject booking = jarr.getJSONObject(i); 

       //map.put(KEY_RESERVATION_ACTIVE, booking.getString(KEY_RESERVATION_ACTIVE)); 
       reservation.set_active(booking.getString(KEY_RESERVATION_ACTIVE)); 

       //map.put(KEY_RESERVATION_CREATED_AT, booking.getString(KEY_RESERVATION_CREATED_AT)); 
       reservation.set_created_at(booking.getString(KEY_RESERVATION_CREATED_AT)); 

       //map.put(KEY_RESERVATION_DATE, booking.getString(KEY_RESERVATION_DATE)); 
       reservation.set_date(booking.getString(KEY_RESERVATION_DATE)); 

       //map.put(KEY_RESERVATION_END_TIME, booking.getString(KEY_RESERVATION_END_TIME)); 
       reservation.set_end_time(booking.getString(KEY_RESERVATION_END_TIME)); 

       //map.put(KEY_RESERVATION_ID, booking.getString(KEY_RESERVATION_ID)); 
       reservation.set_id(booking.getInt(KEY_RESERVATION_ID)); 

       //map.put(KEY_RESERVATION_NAME, booking.getString(KEY_RESERVATION_NAME)); 
       reservation.set_rest_name(booking.getString(KEY_RESERVATION_NAME)); 

       //map.put(KEY_RESERVATION_PARTY_SIZE, booking.getString(KEY_RESERVATION_PARTY_SIZE)); 
       reservation.set_party_size(booking.getString(KEY_RESERVATION_PARTY_SIZE)); 

       //map.put(KEY_RESERVATION_PHONE, booking.getString(KEY_RESERVATION_PHONE)); 
       reservation.set_phone(booking.getString(KEY_RESERVATION_PHONE)); 

       //map.put(KEY_RESERVATION_RESTAURANT_ID, booking.getString(KEY_RESERVATION_RESTAURANT_ID)); 
       reservation.set_restaurant_id(booking.getString(KEY_RESERVATION_RESTAURANT_ID)); 

       //map.put(KEY_RESERVATION_SPECIAL_REQUEST, booking.getString(KEY_RESERVATION_SPECIAL_REQUEST)); 
       reservation.set_special_request(booking.getString(KEY_RESERVATION_SPECIAL_REQUEST)); 

       //map.put(KEY_RESERVATION_START_TIME, booking.getString(KEY_RESERVATION_START_TIME)); 
       reservation.set_start_time(booking.getString(KEY_RESERVATION_START_TIME)); 

       //map.put(KEY_RESERVATION_TABLE, booking.getString(KEY_RESERVATION_TABLE)); 
       reservation.set_table(booking.getString(KEY_RESERVATION_TABLE)); 


       //map.put(KEY_RESERVATION_UPDATED, booking.getString(KEY_RESERVATION_UPDATED)); 
       reservation.set_updated_at(booking.getString(KEY_RESERVATION_UPDATED)); 

       //map.put(KEY_RESERVATION_USER_ID, booking.getString(KEY_RESERVATION_USER_ID)); 
       reservation.set_user_id(booking.getString(KEY_RESERVATION_USER_ID)); 
       userId = booking.getString(KEY_RESERVATION_USER_ID); 


       //map.put(AllLabels.KEY_RESTAURANT_MISC, booking.getString(AllLabels.KEY_RESTAURANT_MISC)); 
       //reservation.set_table(booking.getString(AllLabels.KEY_RESTAURANT_MISC)); 

       //map.put(AllLabels.KEY_RESTAURANT_ARRIVED, booking.getString(AllLabels.KEY_RESTAURANT_ARRIVED)); 
       //reservation.set_table(booking.getString(AllLabels.KEY_RESTAURANT_ARRIVED)); 

       //map.put(AllLabels.KEY_RESTAURANT_ARRIVED, booking.getString(AllLabels.KEY_RESTAURANT_EMAIL)); 
       //reservation.set_table(booking.getString(AllLabels.KEY_RESTAURANT_EMAIL)); 

      //     map.put(AllLabels.KEY_RESTAURANT_ARRIVED, booking.getString(AllLabels.KEY_SPECIAL_REQUEST)); 
     //     reservation.set_table(booking.getString(AllLabels.KEY_SPECIAL_REQUEST)); 
    //     

       restaurant = db.getRestaurantDetail(Integer.valueOf(booking.getString(KEY_RESERVATION_RESTAURANT_ID))); 

      //map.put(KEY_RESERVATION_RESTAURANT_NAME, restaurant.get_name()); 
       System.out.println(restaurant.get_name()); 
       //reservation.set_rest_name(restaurant.get_name()); 
       //db.addReservation(reservation); 


       //bookingList.add(map); 
      } 
      isParsingCompleted = true; 
      System.out.println(isParsingCompleted); 
     } 
     catch (Exception e) { 
      e.printStackTrace(); 
      isUserAuth = false; 
      isParsingCompleted = false; 
      return null; 
     } 
     return null; 
    } 

    protected void onPostExecute(String file_url) { 
     super.onPostExecute(file_url); 
     Log.d("flow", "MyReservation:onPostExecute"); 
     if (showProcessing) { 
      pDialog.dismiss(); 
     } 
     if ((res_code != 200 && res_code != 201) /*|| bookingList.size() < 1*/ || !isParsingCompleted) { 
      downloadReservationListener.errorDownloadingReservation(isUserAuth, errorMsg); 
     } 
     else { 
      isParsingCompleted = true; 
      ((Activity)context).runOnUiThread(new Runnable() { 
       public void run() { 

        downloadReservationListener.successfullyDownloadedReservation(userId); 

       } 
      }); 
     } 
    } 
} 

DialogInterface.OnClickListener reservationListener = new DialogInterface.OnClickListener() { 
    public void onClick(DialogInterface dialog,int id) { 
     // if this button is clicked, just close 
     // the dialog box and do nothing 
     dialog.cancel(); 
     removeFragment(); 
    } 
}; 

private void removeFragment() { 
    ((MainActivity)context).removeFragment(); 
} 

}

Answer 1

我覺得restaurant爲空。所以，當你想在println()得到它的名字，它拋出nullpointer。

所以只是檢查這兩條線：

 restaurant = db.getRestaurantDetail(Integer.valueOf(booking.getString(KEY_RESERVATION_RESTAURANT_ID))); 
    System.out.println(restaurant.get_name()); 

，並確保沒有價值restaurant;