خطا در اتصال به سرور و دریافت json به کمک کتابخانه volley

این کلاس LoginActivity ام هست. 

package activity;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.android.volley.Request.Method;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.avr.logreg.MainActivity;
import com.avr.logreg.R;

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

import java.util.HashMap;
import java.util.Map;

import app.AppConfig;
import app.AppController;
import helper.SQLiteHandler;
import helper.SessionManager;


public class LoginActivity extends Activity {
  private static final String TAG = RegisterActivity.class.getSimpleName();
  private Button btnLogin;
  private Button btnLinkToRegister;
  private EditText inputEmail;
  private EditText inputPassword;
  private ProgressDialog pDialog;
  private SessionManager session;
  private SQLiteHandler db;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);

    inputEmail = (EditText) findViewById(R.id.email);
    inputPassword = (EditText) findViewById(R.id.password);
    btnLogin = (Button) findViewById(R.id.btnLogin);
    btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen);

    // Progress dialog
    pDialog = new ProgressDialog(this);
    pDialog.setCancelable(false);

    // SQLite database handler
    db = new SQLiteHandler(getApplicationContext());

    // Session manager
    session = new SessionManager(getApplicationContext());

    // Check if user is already logged in or not
    if (session.isLoggedIn()) {
      // User is already logged in. Take him to main activity
      Intent intent = new Intent(LoginActivity.this, MainActivity.class);
      startActivity(intent);
      finish();
    }

    // Login button Click Event
    btnLogin.setOnClickListener(new View.OnClickListener() {

      public void onClick(View view) {
        String email = inputEmail.getText().toString().trim();
        String password = inputPassword.getText().toString().trim();


        // Check for empty data in the form
        if (!email.isEmpty() && !password.isEmpty()) {
          // login user
          checkLogin(email, password);
        } else {
          // Prompt user to enter credentials
          Toast.makeText(getApplicationContext(),
            "Please enter the credentials!", Toast.LENGTH_LONG)
            .show();
        }
      }

    });

    // Link to Register Screen
    btnLinkToRegister.setOnClickListener(new View.OnClickListener() {

      public void onClick(View view) {
        Intent i = new Intent(getApplicationContext(),
          RegisterActivity.class);
        startActivity(i);
        finish();
      }
    });

  }

  /**
   * function to verify login details in mysql db
   * */
  private void checkLogin(final String email, final String password) {
    // Tag used to cancel the request
    String tag_string_req = "req_login";

    pDialog.setMessage("Logging in ...");
    showDialog();

    StringRequest strReq = new StringRequest(Method.POST,
      AppConfig.URL_LOGIN, new Response.Listener<String>() {

      @Override
      public void onResponse(String response) {
        Log.d(TAG, "Login Response: " + response.toString());
        hideDialog();

        try {
          JSONObject jObj = new JSONObject(response);
          boolean error = jObj.getBoolean("error");

          // Check for error node in json
          if (!error) {
            // user successfully logged in
            // Create login session
            session.setLogin(true);

            // Now store the user in SQLite
            String uid = jObj.getString("uid");

            JSONObject user = jObj.getJSONObject("user");
            String name = user.getString("name");
            String email = user.getString("email");
            String created_at = user
              .getString("created_at");

            // Inserting row in users table
            db.addUser(name, email, uid, created_at);

            // Launch main activity
            Intent intent = new Intent(LoginActivity.this,
              MainActivity.class);
            startActivity(intent);
            finish();
          } else {
            // Error in login. Get the error message
            String errorMsg = jObj.getString("error_msg");
            Toast.makeText(getApplicationContext(),
              errorMsg, Toast.LENGTH_LONG).show();
          }
        } catch (JSONException e) {
          // JSON error
          e.printStackTrace();
          Toast.makeText(getApplicationContext(), "Json error: " + e.getMessage(), Toast.LENGTH_LONG).show();
        }

      }
    }, new Response.ErrorListener() {

      @Override
      public void onErrorResponse(VolleyError error) {
        Log.e(TAG, "Login Error: " + error.getMessage());
        Toast.makeText(getApplicationContext(),
          error.getMessage(), Toast.LENGTH_LONG).show();
        hideDialog();
      }
    }) {

      @Override
      protected Map<String, String> getParams() {
        // Posting parameters to login url
        Map<String, String> params = new HashMap<String, String>();
        params.put("email", email);
        params.put("password", password);

        return params;
      }

    };

    // Adding request to request queue
    AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
  }

  private void showDialog() {
    if (!pDialog.isShowing())
      pDialog.show();
  }

  private void hideDialog() {
    if (pDialog.isShowing())
      pDialog.dismiss();
  }
}

این هم کل logcat  موقع crash  کردن برنامه :

08-11 09:21:33.855 1513-1513/com.avr.logreg E/Trace: error opening trace file: No such file or directory (2)
08-11 09:21:36.022 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.monkeyPatchExistingResources
08-11 09:21:36.024 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.pruneResourceCache
08-11 09:21:36.286 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.294 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.294 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.294 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.media.session.MediaController', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.294 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.widget.Toolbar', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.app.ActivityManager$TaskDescription', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.app.SharedElementCallback', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.transition.TransitionManager', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.app.SharedElementCallback', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.app.assist.AssistContent', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.view.SearchEvent', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method activity.LoginActivity.access$super
08-11 09:21:36.304 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method activity.LoginActivity.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.app.Application$OnProvideAssistDataListener', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.os.UserHandle', referenced from method app.AppController.access$super
08-11 09:22:04.494 1513-1513/com.avr.logreg E/dalvikvm: Could not find class 'android.app.Application$OnProvideAssistDataListener', referenced from method app.AppController.access$super
08-11 09:22:04.545 1513-1513/com.avr.logreg E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at activity.LoginActivity.checkLogin(LoginActivity.java:187)
at activity.LoginActivity.access$200(LoginActivity.java:32)
at activity.LoginActivity$1.onClick(LoginActivity.java:81)
at android.view.View.performClick(View.java:4084)
at android.view.View$PerformClick.run(View.java:16966)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)

public class AppController extends Application {

  public static final String TAG = AppController.class.getSimpleName();

  private RequestQueue mRequestQueue;

  private static AppController mInstance;

  @Override
  public void onCreate() {
    super.onCreate();
    mInstance = this;
  }

  public static synchronized AppController getInstance() {
    return mInstance;
  }

  public RequestQueue getRequestQueue() {
    if (mRequestQueue == null) {
      mRequestQueue = Volley.newRequestQueue(getApplicationContext());
    }

    return mRequestQueue;
  }

  public <T> void addToRequestQueue(Request<T> req, String tag) {
    req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
    getRequestQueue().add(req);
  }

  public <T> void addToRequestQueue(Request<T> req) {
    req.setTag(TAG);
    getRequestQueue().add(req);
  }

  public void cancelPendingRequests(Object tag) {
    if (mRequestQueue != null) {
      mRequestQueue.cancelAll(tag);
    }
  }
}

 بجای استفاده از تابع زیر  

AppController.getInstance().addToRequestQueue(strReq, tag_string_req);

خیلی ساده  strReq رو به queue اضافه کردم:

 
queue.add(strReq);