BufferedReader / AsynchTask- java.lang.NullPointerException：锁== null

Question

I am working on an Android App and I am stuck on an error. I am attempting to communicate with a server and get a JSON object from that server. I made a class called ServerCommunication which extends AsynchTask. My server communication class has the standard doInBackground() method. In this method, I try to parse a JSON object from a webpage but an exception is thrown in that method.

I should mention im running my server locally on my machine for now. Therefore, the url im passing my ServerCommunication is: http://127.0.0.1:9000/getVehicle/2942 . This webpage contains plain text of a JSON object. Ill include the JSON object at the bottom.

The exception is: java.lang.NullPointerException: lock == null . This exception is thrown in the second try-catch.

The line that causes this exception is:

BufferedReader reader = new BufferedReader(new InputStreamReader(
                        is, "iso-8859-1"), 8);

This is line has an error because my InputStream is is null. For some reason, this line is throwing an exception which is why is is null. Ill include my log output for this at the end of this post

    HttpResponse httpResponse = httpClient.execute(httpPost);

Here is my ServerCommunication class:

class ServerCommunication extends AsyncTask<String, Integer, JSONObject> {

    public ServerResponse delegate = null;
    public JSONObject jResult;

    // this is called whenever you call puhlishProgress(Integer), for example
    // when updating a progressbar when downloading stuff
    protected void onProgressUpdate(Integer... progress) {

    }

    // the onPostexecute method receives the return type of doInBackGround()
    protected void onPostExecute(JSONObject result) {
        delegate.processFinish(result);
    }

    @Override
    protected JSONObject doInBackground(String... params) {

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

        Log.e("Params 0", params[0]);

        try {
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(params[0]);
            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);
            }

            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 jObj;
    }
}

Here is the JSON Object I am trying to parse:

{"Bus":[{"pkey":604,"vehicle_id":261,"trip_id":945162,"route_id":2942,"stop_id":1847,"latitude":43.26762008666992,"longitude":-79.9635009765625,"speed":3.0,"label":"504","bearing":110.0,"odometer":1329300.0,"timestamp":1420775313},{"pkey":605,"vehicle_id":284,"trip_id":945024,"route_id":2942,"stop_id":1926,"latitude":43.22480010986328,"longitude":-79.7864990234375,"speed":10.0,"label":"703","bearing":296.0,"odometer":9481600.0,"timestamp":1420775308},{"pkey":607,"vehicle_id":388,"trip_id":944939,"route_id":2942,"stop_id":1368,"latitude":43.247520446777344,"longitude":-79.84809875488281,"speed":12.0,"label":"1008","bearing":288.0,"odometer":2.21116E+7,"timestamp":1420775317},{"pkey":610,"vehicle_id":422,"trip_id":945158,"route_id":2942,"stop_id":2145,"latitude":43.2575798034668,"longitude":-79.92250061035156,"speed":0.0,"label":"1205","bearing":98.0,"odometer":203000.0,"timestamp":1420775296},{"pkey":623,"vehicle_id":402,"trip_id":945023,"route_id":2942,"stop_id":1955,"latitude":43.25736999511719,"longitude":-79.87146759033203,"speed":8.0,"label":"1102","bearing":286.0,"odometer":5067800.0,"timestamp":1420775311},{"pkey":630,"vehicle_id":276,"trip_id":945154,"route_id":2942,"stop_id":3089,"latitude":43.25257110595703,"longitude":-79.85984802246094,"speed":4.0,"label":"518","bearing":184.0,"odometer":5778500.0,"timestamp":1420775286},{"pkey":634,"vehicle_id":294,"trip_id":945161,"route_id":2942,"stop_id":1923,"latitude":43.23030090332031,"longitude":-79.79962158203125,"speed":13.0,"label":"713","bearing":110.0,"odometer":1.7729E+7,"timestamp":1420775313},{"pkey":639,"vehicle_id":335,"trip_id":944997,"route_id":2942,"stop_id":1320,"latitude":43.257320404052734,"longitude":-79.93509674072266,"speed":2.0,"label":"819","bearing":272.0,"odometer":4.09802E+7,"timestamp":1420775293},{"pkey":653,"vehicle_id":425,"trip_id":944985,"route_id":2942,"stop_id":2560,"latitude":43.23651885986328,"longitude":-79.97097778320312,"speed":13.0,"label":"1208","bearing":210.0,"odometer":5824800.0,"timestamp":1420775288},{"pkey":660,"vehicle_id":317,"trip_id":945168,"route_id":2942,"stop_id":2530,"latitude":43.20967102050781,"longitude":-79.78714752197266,"speed":0.0,"label":"801","bearing":272.0,"odometer":428900.0,"timestamp":1420775282}]}

Log Output

01-09 00:05:29.053: W/System.err(21902): org.apache.http.conn.HttpHostConnectException: Connection to http://127.0.0.1:9000 refused
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:235)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:167)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:125)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.client.DefaultRequestDirector.executeOriginal(DefaultRequestDirector.java:1227)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:677)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:567)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:491)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:469)
01-09 00:05:29.053: W/System.err(21902):    at com.example.myshuttle.ServerCommunication.doInBackground(ServerCommunication.java:46)
01-09 00:05:29.053: W/System.err(21902):    at com.example.myshuttle.ServerCommunication.doInBackground(ServerCommunication.java:1)
01-09 00:05:29.053: W/System.err(21902):    at android.os.AsyncTask$2.call(AsyncTask.java:288)
01-09 00:05:29.053: W/System.err(21902):    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
01-09 00:05:29.053: W/System.err(21902):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
01-09 00:05:29.053: W/System.err(21902):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
01-09 00:05:29.053: W/System.err(21902):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
01-09 00:05:29.053: W/System.err(21902):    at java.lang.Thread.run(Thread.java:841)
01-09 00:05:29.053: W/System.err(21902): Caused by: java.net.ConnectException: failed to connect to /127.0.0.1 (port 9000): connect failed: ECONNREFUSED (Connection refused)
01-09 00:05:29.053: W/System.err(21902):    at libcore.io.IoBridge.connect(IoBridge.java:114)
01-09 00:05:29.053: W/System.err(21902):    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
01-09 00:05:29.053: W/System.err(21902):    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:460)
01-09 00:05:29.053: W/System.err(21902):    at java.net.Socket.connect(Socket.java:833)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
01-09 00:05:29.053: W/System.err(21902):    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:188)
01-09 00:05:29.053: W/System.err(21902):    ... 15 more
01-09 00:05:29.053: W/System.err(21902): Caused by: libcore.io.ErrnoException: connect failed: ECONNREFUSED (Connection refused)
01-09 00:05:29.053: W/System.err(21902):    at libcore.io.Posix.connect(Native Method)
01-09 00:05:29.053: W/System.err(21902):    at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:85)
01-09 00:05:29.053: W/System.err(21902):    at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
01-09 00:05:29.053: W/System.err(21902):    at libcore.io.IoBridge.connect(IoBridge.java:112)
01-09 00:05:29.053: W/System.err(21902):    ... 20 more

Any suggestions?

Answer 1

Here

sb.append(line + "n"); <<<<<

You are adding n with each line when reading data from BufferedReader which make invalid json string.

Just read and append data in StringBuilder :

   while ((line = reader.readLine()) != null) {
        sb.append(line);
    }

Also before passing InputStream to InputStreamReader make sure is is not null .

Answer 2

I wrote a helper class for WebService connection. I think you can try with it.

 public class ServiceHelper {
    /**
     * Get conten from url
     * 
     * @param url
     * @return
     */
    public static String getHttp(String url) {
        // Get the HTML response
        HttpClient client = new DefaultHttpClient();
        HttpGet request = new HttpGet(url);
        HttpResponse response;
        try {
            response = client.execute(request);
            return parseStringFromResponse(response);
        } catch (Exception e) {

        }
        return "";
    }

    /**
     * Post content to url
     * 
     * @param url
     * @param params
     * @return
     */
    public static String postHttp(String url, List<NameValuePair> params) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(url);
        try {
            // Add params if need
            if (params != null && !params.isEmpty()) {
                httppost.setEntity(new UrlEncodedFormEntity(params));
            }
            // Execute HTTP Post Request
            HttpResponse response = httpclient.execute(httppost);
            return parseStringFromResponse(response);
        } catch (Exception e) {

        }
        return "";
    }

    /**
     * Parse string from {@link HttpResponse}
     * 
     * @param response
     * @return
     * @throws Exception
     */
    public static final String parseStringFromResponse(
            final HttpResponse response) throws Exception {
        InputStream in = response.getEntity().getContent();
        BufferedReader reader = new BufferedReader(
                new InputStreamReader(in));
        StringBuilder str = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            str.append(line);
        }
        in.close();
        return str.toString();
    }
}

Answer 3

So I found my problem:

I was running my server locally on my laptop on port 9000. I could access my server on my laptop by using localhost:9000 .

I was running my android app on my tablet. Therefore when my tablet tried to access localhost:9000 , my tablet was trying to access its own local host, not my laptop.

To fix this error, the url I had to pass my tablet was MyLaptopIP:9000 . I also had to ensure that my laptop and tablet were on the same network.