错误解析JSON到Java对象：显示java.lang.NullPointerException [英] Error parsing json to java object: java.lang.NullPointerException

问题描述

我创建登录系统我的应用程序。它发送的登录信息的API，并返回一个JSON。

I'm creating login system for my application. It's sends the login information to the API and return a json.

这是LoginActivity.java

This is LoginActivity.java

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

        // Login Button Click event
        Button btnLogin = (Button) findViewById(R.id.btnLogin);
        btnLogin.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                this.retrieveLogin();
            }

            private void retrieveLogin() {
                LoginAsyncTask task = new LoginAsyncTask();
                task.execute();
            }

        });

        // Link to Register Screen
        Button btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegister);
        btnLinkToRegister.setOnClickListener(new View.OnClickListener() {
                public void onClick(View view) {
                    Intent i = new Intent(getApplicationContext(),RegisterActivity.class);
                    startActivity(i);
                    finish();
                }
        });   
    }

    private class LoginAsyncTask extends AsyncTask<Void, Void, Void> {
        Login login2;
        private Activity activity;

        final EditText inputEmail = (EditText) findViewById(R.id.loginEmail);
        final EditText inputPassword = (EditText) findViewById(R.id.loginPassword);
        final TextView loginErrorMsg = (TextView) findViewById(R.id.login_error);

        String email = inputEmail.getText().toString();
        String pwrd = inputPassword.getText().toString();


        @Override
        protected Void doInBackground(Void... params) {
            //System.out.println(loginURL);
            try {
                //Create an HTTP client
                DefaultHttpClient client = new DefaultHttpClient();
                HttpPost post = new HttpPost(loginURL);

                //Perform the request and check the status code
                HttpResponse response = client.execute(post);
                StatusLine statusLine = response.getStatusLine();
                if(statusLine.getStatusCode() == 200) {
                    HttpEntity entity = response.getEntity();
                    InputStream content = entity.getContent();

                    try {
                        //Read the server response and attempt to parse it as JSON
                        Reader reader = new InputStreamReader(content);

                        Gson gson = new Gson();
                        this.login2 = gson.fromJson(reader, Login.class);
                    } catch (Exception ex) {
                        Log.e(TAG, "Failed to parse JSON due to: " + ex);
                        failedLoading();
                    }
                } else {
                    Log.e(TAG, "Server responded with status code: " + statusLine.getStatusCode());
                    failedLoading();
                }
            } catch(Exception ex) {
                Log.e(TAG, "Failed to send HTTP POST request due to: " + ex);
                failedLoading();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {

        }
    }

    @Override
    protected void onPause() {

        super.onPause();
        //finish();
    }
    private void failedLoading() {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(LoginActivity.this, "Failed to Register. look at LogCat.", Toast.LENGTH_SHORT).show();
            }
        });
    }   
}

如果我输入无效数据登录其返回以下JSON：

If I enter invalid data for login its return following json:

{
"result":"KO",
"message":["Make sure you did not misspell your password."]
}

该消息显示TextView的成功。

The message is display on the textview successfully.

但是，当我输入登录其返回以下JSON有效数据：

But when I enter valid data for login its return following json:

{
"result":"OK",
"message":["Successfull login."],
"values":{"id":"1809","fname":"me","gender":"male"}
}

在这种情况下，我的应用程序强制关闭，并得到以下的logcat：

In this situation my application force closes and gets following logcat:

    09-30 12:55:05.445: E/AndroidRuntime(14593): FATAL EXCEPTION: main
09-30 12:55:05.445: E/AndroidRuntime(14593): java.lang.NullPointerException
09-30 12:55:05.445: E/AndroidRuntime(14593):    at com.kabelash.sk.LoginActivity$LoginAsyncTask.onPostExecute(LoginActivity.java:128)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at com.kabelash.sk.LoginActivity$LoginAsyncTask.onPostExecute(LoginActivity.java:1)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at android.os.AsyncTask.finish(AsyncTask.java:631)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at android.os.Handler.dispatchMessage(Handler.java:99)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at android.os.Looper.loop(Looper.java:137)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at android.app.ActivityThread.main(ActivityThread.java:4898)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at java.lang.reflect.Method.invokeNative(Native Method)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at java.lang.reflect.Method.invoke(Method.java:511)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
09-30 12:55:05.445: E/AndroidRuntime(14593):    at dalvik.system.NativeStart.main(Native Method)

但我找不到它的任何解决方案。有人请帮助。

But I couldn't find any solution for it. Someone please help.

推荐答案

我需要你的价值类。因为您的变量也许整数类decleration。在JSON数据的标识为字符串

I need your Values class. Because your variable maybe integer decleration in class. In Json data id is string

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