AsyncTask在后台运行身份验证

Question

i am trying a simple authentication page using the AsyncTask. I am running the connection to my webservice in the doInBackground() method and updating the UI in the onPostExecute() method. My webservice simply checks the username and password sent to it and returns a JSON object. As long as the webservice is up and returns the JSON object this code works fine. But when the service is down and the connection fails i get the error i have attached below.

Here is my code :

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

    public InputStream is = null;
    public JSONObject jObj = null;
    public String json = "";
    public int flag = 0;

    protected JSONObject doInBackground(String... urls) {
        HttpClient client = new DefaultHttpClient();  
        String getURL = "http://MYWEBSERVICE";
        HttpGet get = new HttpGet(getURL);
        get.addHeader("authorization", urls[0]);
        HttpResponse responseGet;

        try {

            responseGet = client.execute(get);
            HttpEntity httpEntity = responseGet.getEntity();
            is = httpEntity.getContent();  
             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");
                        System.out.println("Authentication status: "+sb.toString());
                    }
                    is.close();

                    json = sb.toString();
                    try {
                        jObj = new JSONObject(json);
                    } catch (JSONException e) {
                        Log.e("JSON Parser", "Error parsing data " + e.toString());
                    }



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


        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block

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

            System.out.println("this is where connection errors are caught!");
        jObj.put("authentication", "cfailed");
                return jObj;
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }

        }
            return jObj;
    }


    protected void onPostExecute(JSONObject result) {
         String auth;
         String notes;

        try {
            auth = jObj.getString("authentication");
            notes = jObj.getString("note");

            if (auth.equalsIgnoreCase("cfailed"))
            {
                emessage.setTextColor(RED);
                emessage.setText("Connection to server failed");
            }
            else
            {
            if (auth.equalsIgnoreCase("Successfull"))
                    {
                // TODO login to page   

            }else if(auth.equalsIgnoreCase("unSuccessfull"))
            {
                emessage.setText(notes);
                emessage.setTextColor(RED);
                if(notes.contains("password"))
                    lpass.setTextColor(RED);
                else if(notes.contains("name"))
                    luname.setTextColor(RED); 


            }
            }
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

Logcat :

  01-03 13:22:13.567: E/AndroidRuntime(334): FATAL EXCEPTION: AsyncTask #1
  01-03 13:22:13.567: E/AndroidRuntime(334): java.lang.RuntimeException: An error occured while executing doInBackground()
  01-03 13:22:13.567: E/AndroidRuntime(334): atandroid.os.AsyncTask$3.done(AsyncTask.java:200)
  01-03 13:22:13.567: E/AndroidRuntime(334):at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
 01-03 13:22:13.567: E/AndroidRuntime(334): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
 01-03 13:22:13.567: E/AndroidRuntime(334):at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
 01-03 13:22:13.567: E/AndroidRuntime(334):at java.util.concurrent.FutureTask.run(FutureTask.java:137)
 01-03 13:22:13.567: E/AndroidRuntime(334):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
 01-03 13:22:13.567: E/AndroidRuntime(334):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
 01-03 13:22:13.567: E/AndroidRuntime(334):     at java.lang.Thread.run(Thread.java:1096)
 01-03 13:22:13.567: E/AndroidRuntime(334): Caused by: java.lang.NullPointerException
 01-03 13:22:13.567: E/AndroidRuntime(334):     at com.cyberink.asyncauth.login$AuthneticateTask.doInBackground(login.java:194)
 01-03 13:22:13.567: E/AndroidRuntime(334):     at com.cyberink.asyncauth.login$AuthneticateTask.doInBackground(login.java:1)
 01-03 13:22:13.567: E/AndroidRuntime(334):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
 01-03 13:22:13.567: E/AndroidRuntime(334):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
 01-03 13:22:13.567: E/AndroidRuntime(334):     ... 4 more

Answer 1

replace jObj.put("authentication", "cfailed"); with

 jObj=new JSONObject();
 jObj.put("authentication", "cfailed");

and change your current onPostExecute as :

protected void onPostExecute(JSONObject result) {
         String auth;
         String notes;
       // check here if result if null or not
       if(result !=null){
         try {
             auth = result.getString("authentication");
             notes = result.getString("note");
             // your code here      
           } catch (JSONException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
           }
       }
      else{
           // code here if json null
       }

    }

Answer 2

Hey after close observation of your code, I found that it was due to NullPointerException caused by jObj (JsonObject). As you posted in the code check that jObj is initialized as null and Object was created only when web service executed successfully. But when Connection error occured it was thrown to IOException block where you are directly putting the key value pairs without creating object. Add one more line jObj = new JsonObject(); before 194th line. Hope it solves your issue.