외부 데이터베이스에 연결 안드로이드 발생 원인 : java.lang.NullPointerException

Question

나는 첫 번째 안드로이드 애플 리케이션을 만드는 과정에 있으며,이 앱의 목표는 외부 데이터베이스에 연결하는 것입니다. 아래 구문은 java.lang.NullPointerException 오류 메시지를 제공합니다. 아래는 나의 모든 구문과 logcat 정보입니다. 내가 도대체 ​​뭘 잘못하고있는 겁니까?

MainActivity

package com.example.connecttoexternaldatabase; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.support.v7.app.ActionBarActivity; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.TextView; 

public class MainActivity extends ActionBarActivity { 

private TextView responseTextView; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    responseTextView = (TextView) findViewById(R.id.responseTextView); 

    new GetAllCustomerTask().execute(new ApiConnector()); 
} 

public void setTextToTextView(JSONArray jsonArray){ 
    String theTextToDisplayOnPhone = ""; 
    for(int i=0; i<jsonArray.length(); i++){ 
     JSONObject json = null; 
     try{ 
      json = jsonArray.getJSONObject(i); 
      theTextToDisplayOnPhone = theTextToDisplayOnPhone + 
        "Name : " +json.getString("FirstName")+" "+ json.get("LastName")+"\n"+ 
        "Age : "+json.getInt("Age")+"\n"+ 
        "Mobile Using : "+json.getString("Mobile")+"\n\n"; 
     } catch (JSONException e){ 
      e.printStackTrace(); 
     } 
    } 

    responseTextView.setText(theTextToDisplayOnPhone); 
} 

private class GetAllCustomerTask extends AsyncTask<ApiConnector, Long, JSONArray>{ 

    @Override 
    protected JSONArray doInBackground(ApiConnector... params) { 
     // is it executed on the background thread 
     return params[0].GetAllCustomers(); 
    } 

    @Override 
    protected void onPostExecute(JSONArray jsonArray){ 
     // it is executed on the main thread 
     setTextToTextView(jsonArray); 
    } 

} 

} 

ApiConnector

package com.example.connecttoexternaldatabase; 

import java.io.IOException; 
import java.net.HttpURLConnection; 

import org.apache.http.HttpEntity; 
import org.apache.http.HttpResponse; 
import org.apache.http.client.ClientProtocolException; 
import org.apache.http.client.methods.HttpGet; 
import org.apache.http.impl.client.DefaultHttpClient; 
import org.apache.http.util.EntityUtils; 
import org.json.JSONArray; 
import org.json.JSONException; 

import android.util.Log; 

public class ApiConnector { 

    public JSONArray GetAllCustomers(){ 
     String url = "http://localhost/app/getAllCustomers.php"; 

     HttpEntity httpEntity = null; 

     try{ 
      DefaultHttpClient httpClient = new DefaultHttpClient(); 
      HttpGet httpGet = new HttpGet(url); 

      HttpResponse httpResponse = httpClient.execute(httpGet); 
      httpEntity = httpResponse.getEntity(); 

     } catch (ClientProtocolException e){ 
      e.printStackTrace(); 
     } catch (IOException e){ 
      e.printStackTrace(); 
     } 

     JSONArray jsonArray = null; 

     if(httpEntity != null){ 
      try{ 
       String entityResponse = EntityUtils.toString(httpEntity); 
       Log.e("Entity Response: ", entityResponse); 
       jsonArray = new JSONArray(entityResponse); 
      } catch (JSONException e){ 
       e.printStackTrace(); 
      } catch (IOException e){ 
       e.printStackTrace(); 
      } 
     } 

     return jsonArray; 
    } 
} 

로그 캣 정보

01-03 13:59:19.599: E/AndroidRuntime(762): FATAL EXCEPTION: main 
01-03 13:59:19.599: E/AndroidRuntime(762): java.lang.NullPointerException 
01-03 13:59:19.599: E/AndroidRuntime(762): at com.example.connecttoexternaldatabase.MainActivity.setTextToTextView(MainActivity.java:31) 
01-03 13:59:19.599: E/AndroidRuntime(762): at com.example.connecttoexternaldatabase.MainActivity$GetAllCustomerTask.onPostExecute(MainActivity.java:58) 
01-03 13:59:19.599: E/AndroidRuntime(762): at com.example.connecttoexternaldatabase.MainActivity$GetAllCustomerTask.onPostExecute(MainActivity.java:1) 
01-03 13:59:19.599: E/AndroidRuntime(762): at android.os.AsyncTask.finish(AsyncTask.java:417) 
01-03 13:59:19.599: E/AndroidRuntime(762): at android.os.AsyncTask.access$300(AsyncTask.java:127) 
01-03 13:59:19.599: E/AndroidRuntime(762): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429) 
01-03 13:59:19.599: E/AndroidRuntime(762): at android.os.Handler.dispatchMessage(Handler.java:99) 
01-03 13:59:19.599: E/AndroidRuntime(762): at android.os.Looper.loop(Looper.java:130) 
01-03 13:59:19.599: E/AndroidRuntime(762): at android.app.ActivityThread.main(ActivityThread.java:3683) 
01-03 13:59:19.599: E/AndroidRuntime(762): at java.lang.reflect.Method.invokeNative(Native Method) 
01-03 13:59:19.599: E/AndroidRuntime(762): at java.lang.reflect.Method.invoke(Method.java:507) 
01-03 13:59:19.599: E/AndroidRuntime(762): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:870) 
01-03 13:59:19.599: E/AndroidRuntime(762): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) 
01-03 13:59:19.599: E/AndroidRuntime(762): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

당신은 당신의 루프에서 null로 된 JSONObject를 설정하는 :

JSONObject json = null; 

을

하지만 어디서나 JSONObject를 만들지 않습니다. 루프 앞에 다음과 같이 입력해야합니다.

JSONObject json = new JSONObject();