Help with servlet, android

[jasmine franco]

What I am trying to do is get a String variable of JSONObject type from the android and then parse it into 4 different variables: lat, lon, start, end. Then use 2 JSONArrays and 2 int arrays, combine 2 int arrays into a JSONArray.Send this JSONarray to the android where it will be used to plot a graph. Somehow, the response is not getting delivered to the android. please help me.

The servlet code is like this:

@WebServlet("/MyServlet")
public class DoubleMeServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
    
        Long lat;
	Long lon;
	String start = "";
	String end ="";
		String sentString;
	Date date ;
	Date date1;
	long timeSum = 0; // 
	int i;
int[] timeUnix = {1423502074, 1423588474, 1423674874, 1423761274, 1423847674, 1423934074, 1424020474, 1424106874, 1424193274};
int [] db = {1000,2030,3930,4030,5030,6300,7300,8300,9380}; 
int[] timeResult = new int[9];
int[] dbResult = new int[9];
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    	
    	try {
            int length = request.getContentLength();
            byte[] input = new byte[length];
           
            ServletInputStream sin = request.getInputStream();
            int c, count = 0 ;
            while ((c = sin.read(input, count, input.length-count)) != -1) {
            	count +=c;
}
            sin.close();
           // explicitly create a String object and assign the Byte array to it
            String recievedString = new String(input);
            response.setStatus(HttpServletResponse.SC_OK);
            OutputStreamWriter writer = new OutputStreamWriter(response.getOutputStream());
           
			try {
				 JSONObject jo = new JSONObject(recievedString);
			
            lon = (Long) jo.get("longitude");
            lat = (Long) jo.get("latitude");
            start = (String) jo.getString("start");
            end = (String) jo.getString("end");
            
			} catch (JSONException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
            
         // start, end from string to date
            try{
            	date = format.parse(start);
            	date1 = format.parse(end);
            	}catch(ParseException e){
            	e.printStackTrace();
            	}
          
        		  JSONArray arrayTime = new JSONArray();
        		    for(int k = 0; k < timeUnix.length; k++)
        		    {
        		    		try {
								arrayTime.put(k, timeUnix[k]);
							} catch (JSONException e) {
								// TODO Auto-generated catch block
								e.printStackTrace();
							}
        		    }
        		    
        		    JSONArray arrayDB = new JSONArray();
        		    for(int l = 0; l < db.length; l++)
        		   {
        		    	try {
        		    		arrayDB.put(l, db[l]);
        		    	} catch (JSONException e) {
        		    		e.printStackTrace();
        		    	}
        		    }
        		    
        		    
        		    JSONArray GraphData = new JSONArray(); // creating graph data
        		    try {
        		    	GraphData.put(0, timeUnix);
        		    	GraphData.put(1, db);
        		    } catch (JSONException e){
        		    e.printStackTrace();
        		    }
        		  
        		    	for(int timeRes = 0; timeRes < timeUnix.length ; timeRes++)
        		    	{
        		    		try {
								timeResult[timeRes] = arrayTime.getInt(timeRes);
							} catch (JSONException e) {
								// TODO Auto-generated catch block
								e.printStackTrace();
							}
        		    	}
        		    
        		    try {
        		    	for(int dbRes = 0; dbRes < db.length; dbRes++)
        		    	{
        		    		dbResult[dbRes] = arrayDB.getInt(dbRes);
        		    	}
        		    } catch (JSONException e) {
		    			e.printStackTrace();
		    		}
        		    
                 	sentString = GraphData.toString(); // combined JSONArray to string 
            
                 	 writer.write(sentString);
                     writer.flush();
                     writer.close();
                     
    	} catch (IOException e) {
    		
            try{
                response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
                response.getWriter().print(e.getMessage());
                response.getWriter().close();
            } catch (IOException ioe) {
            }
    	
    	}
    }
    }

The Android code is:

public class GraphActivity extends AppCompatActivity {
    private XYPlot mySimpleXYPlot;
    private double longitude;
    private double latitude;
    private String startTime;
    private String endTime;
    private int code = 0;
    private String sentJSON;
    private JSONArray JSONresultTime;
    private JSONArray JSONresultDB;


   private Number[] time = new Number[9];
   private Number[] noise = new Number[9];

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_graph);
        setUpLabel();
        createMessage();
        Communication communication = new Communication();
        communication.execute("http://**********************");                                  //Enter URL to test
    }

    public class Communication extends AsyncTask<String,String,JSONArray>{

        @Override
        protected JSONArray doInBackground(String... params) {
            URL url;
            HttpURLConnection urlConnection = null;
            JSONArray response = new JSONArray();
            int responseCode;

            try{
                url = new URL(params[0]);                                                       //Set up connection
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setDoOutput(true);
                urlConnection.setRequestMethod("POST");
                urlConnection.setRequestProperty("Content-Type", "application/json");
                responseCode = urlConnection.getResponseCode();
                code = responseCode;

                //Post
                OutputStream output = urlConnection.getOutputStream();                          //Send JSON object to server
                output.write(sentJSON.getBytes());
                output.flush();

                //Receive
                if(responseCode == HttpURLConnection.HTTP_OK){
                    String responseString = readStream(urlConnection.getInputStream());         //Storing server response
                    response = new JSONArray(responseString);                                   //put response into JSON Array object

                    try {                                                                       //Pull out the first array
                        JSONresultTime = response.getJSONArray(0);
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

                    try {                                                                       //Pull out second array
                        JSONresultDB = response.getJSONArray(1);
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

                    try {                                                                       //Parsing first array to local array
                        for (int i = 0; i < time.length; i++) {
                            time[i] = JSONresultTime.getInt(i);
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }

                    try {                                                                       //Parsing second array to local array
                        for (int i = 0; i < noise.length; i++) {
                            noise[i] = JSONresultDB.getInt(i);
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
                else{
                    Log.v("Communication", "Response Code:" + responseCode);
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            } finally{
                if(urlConnection != null){
                    urlConnection.disconnect();
                }
            }
            return response;
        }

        @Override
        protected void onPostExecute(JSONArray response) {
            super.onPostExecute(response);
            setUpGraph();                                                                       //Graph after receiving and parsing data
        }

        private String readStream(InputStream in){                                              //Reading in server response
            BufferedReader reader = null;
            StringBuffer response = new StringBuffer();
            try{
                reader = new BufferedReader(new InputStreamReader(in));
                String line = "";
                while ((line = reader.readLine())!=null){
                    response.append(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if (reader != null){
                    try{
                        reader.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
            return response.toString();
        }
    }

    private void createMessage(){
        JSONObject object = new JSONObject();
        try {
            object.put("longitude",longitude);
            object.put("latitude",latitude);
            object.put("start",startTime);
            object.put("end",endTime);
            sentJSON = object.toString();
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    private void setUpGraph(){
        mySimpleXYPlot = (XYPlot) findViewById(R.id.mySimpleXYPlot);

        // create our series from our array of nums:
        XYSeries series1 = new SimpleXYSeries(Arrays.asList(time), Arrays.asList(noise), "Noise Level");

        LineAndPointFormatter series1Format = new LineAndPointFormatter(Color.RED, Color.GREEN, Color.BLUE, null);

        // add an "dash" effect to the series2 line:

.....................} }
Any help would be highly appreciated. Thanks.

[Dave Tolls]

Narrow it down.
Have you logged what's going on in the servlet so you can check it is actually being hit?
I can't see any logging in there.

Should the servlet work when accessed by the device then the next step is to debug that part of the Android code and log what is coming back.
Again, I don't see any logging (beyond stack traces).

Without some debugging logs to show you what is actually going on then you are flying blind. Staring at code and trying to spot an error is very inefficient compared to having solid data about what is going on inside your app.

[Tim Moores]

What does "the response is not getting delivered" mean, exactly? Which lines of code are or are not being executed on the server? Which lines of code are or are not being executed on the client? Are there any exceptions or other messages in either the server logs or the Android logcat?

[jasmine franco]

Dave Tolls wrote:Narrow it down.
Have you logged what's going on in the servlet so you can check it is actually being hit?
I can't see any logging in there.

Should the servlet work when accessed by the device then the next step is to debug that part of the Android code and log what is coming back.
Again, I don't see any logging (beyond stack traces).

Without some debugging logs to show you what is actually going on then you are flying blind. Staring at code and trying to spot an error is very inefficient compared to having solid data about what is going on inside your app.

I don't know how to actually log. I see a log file in the apache tomcat folder but I don't understand much of it.

[jasmine franco]

Tim Moores wrote:What does "the response is not getting delivered" mean, exactly? Which lines of code are or are not being executed on the server? Which lines of code are or are not being executed on the client? Are there any exceptions or other messages in either the server logs or the Android logcat?

The below part of code in Servlet is supposed to provide values in private void setUpGraph() in Android code to these variables : private Number[] time = new Number[9] {};private Number[] noise = new Number[9] .
sentString in servlet should be received at the android end, but it just consider the default values of private Number[] time = new Number[9] {};private Number[] noise = new Number[9] instead of int[] timeUnix = {1423502074, 1423588474, 1423674874, 1423761274, 1423847674, 1423934074, 1424020474, 1424106874, 1424193274};
int [] db = {1000,2030,3930,4030,5030,6300,7300,8300,9380};
int[] timeResult = new int[9];
int[] dbResult = new int[9]; in the servlet.

JSONArray arrayTime = new JSONArray();
                    for(int k = 0; k < timeUnix.length; k++)
                    {
                            try {
                                arrayTime.put(k, timeUnix[k]);
                            } catch (JSONException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }
                    }
                     
                    JSONArray arrayDB = new JSONArray();
                    for(int l = 0; l < db.length; l++)
                   {
                        try {
                            arrayDB.put(l, db[l]);
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                     
                     
                    JSONArray GraphData = new JSONArray(); // creating graph data
                    try {
                        GraphData.put(0, timeUnix);
                        GraphData.put(1, db);
                    } catch (JSONException e){
                    e.printStackTrace();
                    }
                   
                        for(int timeRes = 0; timeRes < timeUnix.length ; timeRes++)
                        {
                            try {
                                timeResult[timeRes] = arrayTime.getInt(timeRes);
                            } catch (JSONException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }
                        }
                     
                    try {
                        for(int dbRes = 0; dbRes < db.length; dbRes++)
                        {
                            dbResult[dbRes] = arrayDB.getInt(dbRes);
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                     
                    sentString = GraphData.toString(); // combined JSONArray to string 
             
                     writer.write(sentString); 

[Stephen M Davies]

I don't know how to actually log. I see a log file in the apache tomcat folder but I don't understand much of it.

You can use android.util.Log;

then you can Log out messages with Log.i / Log.e etc depending on what level you want.

for example to log an error from an Exception.

import android.util.Log;
.....
} catch (Exception e) {
    Log.e("ERROR","Your message",e);
}

Of course you can use this anywhere in your code to log things. The advantage in this over System.out.print is that the Logs colour the messages, making them easier to spot in the Trace, and have extra functionality if needed.

With that in mind, you could also test your servlet in the browser using something like POSTMAN for chrome, which is an excellent free plugin or REST requests. You could even use Chrome dev tools since they are also an excellent resource. Either way you need to see the response you are getting from your server hosting the servlet, it will tell you a lot about whats happening. E.g. if the response code is 404, 500 etc.