Android中的NullPointerException JSONParser

我有一個Android應用程序，每當我按下登錄按鈕時崩潰;我一直在我的JSONParser中得到一個空指針異常。我真的希望你能幫上忙。Android中的NullPointerException JSONParser

這裏是我的UserFunctions.java：

package com.example.sabre9.library; 

import java.util.ArrayList; 
import java.util.List; 

import org.apache.http.NameValuePair; 
import org.apache.http.message.BasicNameValuePair; 
import org.json.JSONObject; 

import android.content.Context; 

public class UserFunctions { 

    private JSONParser jsonParser; 

    // Testing in localhost using wamp or xampp 
    // use http://10.0.2.2/ to connect to your localhost ie http://localhost/ 
    private static String loginURL = "http://10.0.2.2/Sabre1/"; 
    //private static String registerURL = "http://10.0.2.2/Sabre1/"; 

    private static String login_tag = "login"; 
    //private static String register_tag = "register"; 

    // constructor 
    public UserFunctions(){ 
     jsonParser = new JSONParser(); 
    } 

    /** 
    * function make Login Request 
    * @param email 
    * @param password 
    * */ 
    public JSONObject loginUser(String email, String password){ 
     // Building Parameters 
     List<NameValuePair> params = new ArrayList<NameValuePair>(); 
     params.add(new BasicNameValuePair("tag", login_tag)); 
     params.add(new BasicNameValuePair("email", email)); 
     params.add(new BasicNameValuePair("password", password)); 
     JSONObject json = jsonParser.makeHttpRequest(loginURL, "POST", params); 
     // return json 
     // Log.e("JSON", json.toString()); 
     return json; 
    } 

    /** 
    * function make Register Request 
    * @param name 
    * @param email 
    * @param password 
    * */ 
    /* 
    public JSONObject registerUser(String name, String email, String password){ 
     // Building Parameters 
     List<NameValuePair> params = new ArrayList<NameValuePair>(); 
     params.add(new BasicNameValuePair("tag", register_tag)); 
     params.add(new BasicNameValuePair("name", name)); 
     params.add(new BasicNameValuePair("email", email)); 
     params.add(new BasicNameValuePair("password", password)); 


     //getting JSON Object 
     JSONObject json = jsonParser.makeHttpRequest(registerURL, "POST", params); 
     // return json 
     return json; 
    }*/ 

    /** 
    * Function get Login status 
    **/ 
    public boolean isUserLoggedIn(Context context){ 
     DatabaseHandler db = new DatabaseHandler(context); 
     int count = db.getRowCount(); 
     if(count > 0){ 
      // user logged in 
      return true; 
     } 
     return false; 
    } 

    /** 
    * Function to logout user 
    * Reset Database 
    * */ 
    public boolean logoutUser(Context context){ 
     DatabaseHandler db = new DatabaseHandler(context); 
     db.resetTables(); 
     return true; 
    } 
}

JSONParser.java：

package com.example.sabre9.library; 
import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.InputStreamReader; 
import java.io.UnsupportedEncodingException; 
import java.util.List; 

import org.apache.http.HttpEntity; 
import org.apache.http.HttpResponse; 
import org.apache.http.NameValuePair; 
import org.apache.http.client.ClientProtocolException; 
import org.apache.http.client.entity.UrlEncodedFormEntity; 
import org.apache.http.client.methods.HttpGet; 
import org.apache.http.client.methods.HttpPost; 
import org.apache.http.client.utils.URLEncodedUtils; 
import org.apache.http.impl.client.DefaultHttpClient; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.util.Log; 

public class JSONParser { 

     static InputStream is = null; 
     static JSONObject jObj = null; 
     static String json = ""; 

     // constructor 
     public JSONParser() { 

     } 

     // function get json from url 
     // by making HTTP POST or GET mehtod 
     public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params) { 

       // Making HTTP request 
       try { 

         // check for request method 
         if(method == "POST"){ 
           // request method is POST 
           // defaultHttpClient 
           DefaultHttpClient httpClient = new DefaultHttpClient(); 
           HttpPost httpPost = new HttpPost(url); 
           httpPost.setEntity(new UrlEncodedFormEntity(params)); 

           HttpResponse httpResponse = httpClient.execute(httpPost); 
           HttpEntity httpEntity = httpResponse.getEntity(); 
           is = httpEntity.getContent(); 

         }else if(method == "GET"){ 
           // request method is GET 
           DefaultHttpClient httpClient = new DefaultHttpClient(); 
           String paramString = URLEncodedUtils.format(params, "utf-8"); 
           url += "?" + paramString; 
           HttpGet httpGet = new HttpGet(url); 

           HttpResponse httpResponse = httpClient.execute(httpGet); 
           HttpEntity httpEntity = httpResponse.getEntity(); 
           is = httpEntity.getContent(); 
         }      


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

       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(); 
         json = sb.toString(); 
       } catch (Exception e) { 
         Log.e("Buffer Error", "Error converting result " + e.toString()); 
       } 

       // try parse the string to a JSON object 
       try { 
         jObj = new JSONObject(json); 
       } catch (JSONException e) { 
         Log.e("JSON Parser", "Error parsing data " + e.toString()); 
       } 

       // return JSON String 
       return jObj; 

     } 
}

這裏是我的logcat錯誤：

02-13 03:15:01.921: E/Buffer Error(1263): Error converting result java.lang.NullPointerException: lock == null 
02-13 03:15:01.931: E/JSON Parser(1263): Error parsing data org.json.JSONException: End of input at character 0 of 
02-13 03:15:02.891: E/Buffer Error(1263): Error converting result java.lang.NullPointerException: lock == null 
02-13 03:15:02.891: E/JSON Parser(1263): Error parsing data org.json.JSONException: End of input at character 0 of

編輯：我LoginActivity.java：

package com.example.sabre9; 

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

import android.app.Activity; 
import android.content.Intent; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

import com.example.sabre9.library.DatabaseHandler; 
import com.example.sabre9.library.UserFunctions; 

public class LoginActivity extends Activity { 
    Button btnLogin; 
    //Button btnLinkToRegister; 
    EditText inputEmail; 
    EditText inputPassword; 
    TextView loginErrorMsg; 

    // JSON Response node names 
    private static String KEY_SUCCESS = "success"; 
    //private static String KEY_ERROR = "error"; 
    //private static String KEY_ERROR_MSG = "error_msg"; 
    private static String KEY_UID = "uid"; 
    private static String KEY_NAME = "name"; 
    private static String KEY_EMAIL = "email"; 
    private static String KEY_CREATED_AT = "created_at"; 

    private class MyAsyncTask extends AsyncTask<String, Void, JSONObject> { 

     protected JSONObject doInBackground(String... params) { 
       UserFunctions userFunction = new UserFunctions(); 
       if (params.length != 2) 
         return null; 
       JSONObject json = userFunction.loginUser(params[0], params[1]); 
       return json; 
     } 

     protected void onPostExecute(JSONObject json) { 
       try { 
      if (json != null && json.getString(KEY_SUCCESS) != null) { 
       loginErrorMsg.setText(""); 
       String res = json.getString(KEY_SUCCESS); 
       if(Integer.parseInt(res) == 1){ 
        // user successfully logged in 
        // Store user details in SQLite Database 
        DatabaseHandler db = new DatabaseHandler(getApplicationContext()); 
        JSONObject json_user = json.getJSONObject("user"); 

        // Clear all previous From in database 
        UserFunctions userFunction = new UserFunctions(); 
        userFunction.logoutUser(getApplicationContext()); 
        db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT));       

        // Launch Main Screen 
        Intent main = new Intent(getApplicationContext(), MainActivity.class); 

        // Close all views before launching Dashboard 
        main.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
        startActivity(main); 

        // Close Login Screen 
        finish(); 
       }else{ 
        // Error in login 
        loginErrorMsg.setText("Incorrect username/password"); 
       } 
      } 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 
     } 
} 

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

     // Importing all assets like buttons, text fields 
     inputEmail = (EditText) findViewById(R.id.loginEmail); 
     inputPassword = (EditText) findViewById(R.id.loginPassword); 
     btnLogin = (Button) findViewById(R.id.btnLogin); 
     //btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen); 
     loginErrorMsg = (TextView) findViewById(R.id.login_error); 

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

      public void onClick(View view) { 
       String email = inputEmail.getText().toString(); 
       String password = inputPassword.getText().toString();     
       new MyAsyncTask().execute(email, password); 
      } 

     }); 

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

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

來源

2014-02-13 Saint-Clair

如果你能告訴我們異常發生在哪裏，那會很好。 –

當您遇到異常時，請嘗試使用'Log.e（tag，message，throwable）'，以便將異常的堆棧跟蹤寫入LogCat。 – PaF

如果我真的可以告訴，我會的。事情是，我做不到。那些條目是我的logcat中唯一的條目。 –

您的java.lang.NullPointerException: lock == null發生> = Android 3.0，因爲在主（UI）線程上不允許網絡連接，除非通過StrictMode策略覆蓋。嘗試：

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); 
StrictMode.setThreadPolicy(policy);

需要注意的是結果，httpClient.execute(httpPost);會因爲等待響應鎖定系統非常糟糕。（相反，你可以在AsyncTask中這樣做，所以它不鎖定主線程。）希望這有助於。

來源

2014-02-13 09:22:41 unity303

** StrictMode **只能用於遠離網絡操作錯誤。它不是一個正確的方法。因爲你不能在你的實時應用中使用它。它可以避免與網絡相關的錯誤。 – Piyush

我編輯了我的帖子，以便包含我的LoginActivity的代碼。任何想法最好插入你提供的代碼？我的AsyncTask也在那裏陳述。 –

我修復了這個錯誤。似乎通過一個非常尷尬的大腦放屁，我忘記了在我的清單文件中包含所需的互聯網權限。另外，我調整了一些我的php文件。謝謝你的答案:)

來源

2014-02-13 10:17:48

Android中的NullPointerException JSONParser

回答

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