我收到了以下错误消息。 java.lang.NullPointerException：当从服务器获取json文件时，锁= = null。我用Google搜索但无法找到任何解决方案。我使用wamp服务器，mysql和php连接到我的数据库，但是当我尝试注册时，我得到以下错误。
我在第189行和第232行突出显示了块引号中的错误。你能不能帮我解决这些问题。
错误记录
-04 19:41:08.572 2414-2481/com.brad.visor E/Buffer Error﹕ Error converting result java.lang.NullPointerException: lock == null
07-04 19:41:08.572 2414-2481/com.brad.visor E/JSON Parser﹕ Error parsing data org.json.JSONException: End of input at character 0 of
07-04 19:41:08.602 2414-2414/com.brad.visor E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.brad.visor, PID: 2414
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.getString(java.lang.String)' on a null object reference
at com.brad.visor.Register$ProcessRegister.onPostExecute(Register.java:232)
at com.brad.visor.Register$ProcessRegister.onPostExecute(Register.java:189)
at android.os.AsyncTask.finish(AsyncTask.java:636)
at android.os.AsyncTask.access$500(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:653)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Register.java文件
public class Register extends Activity {
/**
* JSON Response node names.
**/
private static String KEY_SUCCESS = "success";
private static String KEY_UID = "uid";
private static String KEY_FIRSTNAME = "fname";
private static String KEY_LASTNAME = "lname";
private static String KEY_USERNAME = "uname";
private static String KEY_EMAIL = "email";
private static String KEY_CREATED_AT = "created_at";
private static String KEY_ERROR = "error";
/**
* Defining layout items.
**/
EditText inputFirstName;
EditText inputLastName;
EditText inputUsername;
EditText inputEmail;
EditText inputPassword;
Button btnRegister;
TextView registerErrorMsg;
/**
* Called when the activity is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.register);
/**
* Defining all layout items
**/
inputFirstName = (EditText) findViewById(R.id.fname);
inputLastName = (EditText) findViewById(R.id.lname);
inputUsername = (EditText) findViewById(R.id.uname);
inputEmail = (EditText) findViewById(R.id.email);
inputPassword = (EditText) findViewById(R.id.pword);
btnRegister = (Button) findViewById(R.id.register);
registerErrorMsg = (TextView) findViewById(R.id.register_error);
/**
* Button which Switches back to the login screen on clicked
**/
Button login = (Button) findViewById(R.id.bktologin);
login.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), Login.class);
startActivityForResult(myIntent, 0);
finish();
}
});
/**
* Register Button click event.
* A Toast is set to alert when the fields are empty.
* Another toast is set to alert Username must be 5 characters.
**/
btnRegister.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if ( ( !inputUsername.getText().toString().equals("")) && ( !inputPassword.getText().toString().equals("")) && ( !inputFirstName.getText().toString().equals("")) && ( !inputLastName.getText().toString().equals("")) && ( !inputEmail.getText().toString().equals("")) )
{
if ( inputUsername.getText().toString().length() > 4 ){
NetAsync(view);
}
else
{
Toast.makeText(getApplicationContext(),
"Username should be minimum 5 characters", Toast.LENGTH_SHORT).show();
}
}
else
{
Toast.makeText(getApplicationContext(),
"One or more fields are empty", Toast.LENGTH_SHORT).show();
}
}
});
}
/**
* Async Task to check whether internet connection is working
**/
private class NetCheck extends AsyncTask<String,String,Boolean>
{
private ProgressDialog nDialog;
@Override
protected void onPreExecute(){
super.onPreExecute();
nDialog = new ProgressDialog(Register.this);
nDialog.setMessage("Loading..");
nDialog.setTitle("Checking Network");
nDialog.setIndeterminate(false);
nDialog.setCancelable(true);
nDialog.show();
}
@Override
protected Boolean doInBackground(String... args){
/**
* Gets current device state and checks for working internet connection by trying Google.
**/
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnected()) {
try {
URL url = new URL("http://www.google.com");
HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
urlc.setConnectTimeout(3000);
urlc.connect();
if (urlc.getResponseCode() == 200) {
return true;
}
} catch (MalformedURLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return false;
}
@Override
protected void onPostExecute(Boolean th){
if(th == true){
nDialog.dismiss();
new ProcessRegister().execute();
}
else{
nDialog.dismiss();
registerErrorMsg.setText("Error in Network Connection");
}
}
}
private class ProcessRegister extends AsyncTask<String, String, JSONObject> { // Error Here
/**
* Defining Process dialog
**/
private ProgressDialog pDialog;
String email,password,fname,lname,uname;
@Override
protected void onPreExecute() {
super.onPreExecute();
inputUsername = (EditText) findViewById(R.id.uname);
inputPassword = (EditText) findViewById(R.id.pword);
fname = inputFirstName.getText().toString();
lname = inputLastName.getText().toString();
email = inputEmail.getText().toString();
uname= inputUsername.getText().toString();
password = inputPassword.getText().toString();
pDialog = new ProgressDialog(Register.this);
pDialog.setTitle("Contacting Servers");
pDialog.setMessage("Registering ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected JSONObject doInBackground(String... args) {
UserFunctions userFunction = new UserFunctions();
JSONObject json = userFunction.registerUser(fname, lname, email, uname, password);
return json;
}
@Override
protected void onPostExecute(JSONObject json) {
/**
* Checks for success message.
**/
try {
if（json.getString（KEY_SUCCESS）！= null）{//这里错误
registerErrorMsg.setText("");
String res = json.getString(KEY_SUCCESS);
String red = json.getString(KEY_ERROR);
if(Integer.parseInt(res) == 1){
pDialog.setTitle("Getting Data");
pDialog.setMessage("Loading Info");
registerErrorMsg.setText("Successfully Registered");
DatabaseHandler db = new DatabaseHandler(getApplicationContext());
JSONObject json_user = json.getJSONObject("user");
/**
* Removes all the previous data in the SQlite database
**/
UserFunctions logout = new UserFunctions();
logout.logoutUser(getApplicationContext());
db.addUser(json_user.getString(KEY_FIRSTNAME),json_user.getString(KEY_LASTNAME),json_user.getString(KEY_EMAIL),json_user.getString(KEY_USERNAME),json_user.getString(KEY_UID),json_user.getString(KEY_CREATED_AT));
/**
* Stores registered data in SQlite Database
* Launch Registered screen
**/
Intent registered = new Intent(getApplicationContext(), Registered.class);
/**
* Close all views before launching Registered screen
**/
registered.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
pDialog.dismiss();
startActivity(registered);
finish();
}
else if (Integer.parseInt(red) ==2){
pDialog.dismiss();
registerErrorMsg.setText("User already exists");
}
else if (Integer.parseInt(red) ==3){
pDialog.dismiss();
registerErrorMsg.setText("Invalid Email id");
}
}
else{
pDialog.dismiss();
registerErrorMsg.setText("Error occured in registration");
}
} catch (JSONException e) {
e.printStackTrace();
}
}}
public void NetAsync(View view){
new NetCheck().execute();
}}
Manifest.java文件
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.brad.visor" >
<application
android:icon="@mipmap/logo"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".Login">
</activity>
<activity
android:name=".Register">
</activity>
<activity
android:name=".Registered">
</activity>
<activity
android:name=".Main">
</activity>
<activity
android:name=".PasswordReset">
</activity>
<activity
android:name=".ChangePassword">
</activity>
</application>
<!-- Allow to connect with internet and to know the current network state-->
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
</manifest>
Userfunction.java代码
public class UserFunctions {
private JSONParser jsonParser;
//URL of the PHP API
private static String loginURL = "http://192.168.0.3:8080/bradvisor_login_api/";
private static String registerURL = "http://192.168.0.3:8080/bradvisor_login_api/";
private static String forpassURL = "http://192.168.0.3:8080/bradvisor_login_api/";
private static String chgpassURL = "http://192.168.0.3:8080/bradvisor_login_api/";
private static String login_tag = "login";
private static String register_tag = "register";
private static String forpass_tag = "forpass";
private static String chgpass_tag = "chgpass";
// constructor
public UserFunctions(){
jsonParser = new JSONParser();
}
/**
* Function to Login
**/
public JSONObject loginUser(String email, String password){
// Building Parameters
List params = new ArrayList();
params.add(new BasicNameValuePair("tag", login_tag));
params.add(new BasicNameValuePair("email", email));
params.add(new BasicNameValuePair("password", password));
JSONObject json = jsonParser.getJSONFromUrl(loginURL, params);
return json;
}
/**
* Function to change password
**/
public JSONObject chgPass(String newpas, String email){
List params = new ArrayList();
params.add(new BasicNameValuePair("tag", chgpass_tag));
params.add(new BasicNameValuePair("newpas", newpas));
params.add(new BasicNameValuePair("email", email));
JSONObject json = jsonParser.getJSONFromUrl(chgpassURL, params);
return json;
}
/**
* Function to reset the password
**/
public JSONObject forPass(String forgotpassword){
List params = new ArrayList();
params.add(new BasicNameValuePair("tag", forpass_tag));
params.add(new BasicNameValuePair("forgotpassword", forgotpassword));
JSONObject json = jsonParser.getJSONFromUrl(forpassURL, params);
return json;
}
/**
* Function to Register
**/
public JSONObject registerUser(String fname, String lname, String email, String uname, String password){
// Building Parameters
List params = new ArrayList();
params.add(new BasicNameValuePair("tag", register_tag));
params.add(new BasicNameValuePair("fname", fname));
params.add(new BasicNameValuePair("lname", lname));
params.add(new BasicNameValuePair("email", email));
params.add(new BasicNameValuePair("uname", uname));
params.add(new BasicNameValuePair("password", password));
JSONObject json = jsonParser.getJSONFromUrl(registerURL,params);
return json;
}
/**
* Function to logout user
* Resets the temporary data stored in SQLite Database
* */
public boolean logoutUser(Context context){
DatabaseHandler db = new DatabaseHandler(context);
db.resetTables();
return true;
}
}
JsonPraser.java文件
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url, List params) {
// Making HTTP request
try {
// 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();
} 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();
Log.e("JSON", json);
} 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;
}
答案 0 :(得分：0)
您可以从另一个异步任务中调用异步任务。问题出在RegisteredUser Function。
答案 1 :(得分：0)
问题似乎是doInBackground正在返回null。因此，当onPostExecute运行时，参数json为null。要避免异常，请在继续执行其余逻辑之前测试json是否为null。您可能必须找出userFunction.registerUser(...)返回null的原因才能真正解决问题。
答案 2 :(得分：0)
（因为你的refisterUser函数返回了一个JsonObject），最好在将它转换为Json之前检查返回的String
添加支票
if(returnedString == null || returnedString == "null") { return; }