Android not getting Json result

Question

Here is my code. This is just a snippet of the whole application. It makes a HTTP request and gets train data from septa. The code is correct as it works in a java project. One note, when I try to do the simple http request part in a separate java class and run it as a java file. In the run it gives me a Fatal Error: Invalid Layout of java.lang.String at value. I tried looking at the thread at this forum. Nothing works. No idea why this is happening. The code was working before!

package com.cs275.septaassignment;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.HttpURLConnection;

import android.app.Activity;
import android.os.Bundle;
import android.os.AsyncTask;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

import com.google.gson.*;

import java.util.ArrayList;

public class TrainInfo extends Activity
{
    protected static String startStation;
    protected static String endStation;

    private ListView listView;//ListView for the output
    private ArrayAdapter<String> adapter;//Adapter to interact with the ListView


    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.train_infolayout);

        startStation = this.getIntent().getExtras().getString("fromStation");
        endStation = this.getIntent().getExtras().getString("toStation");

        ArrayList<String> trainInfo = new ArrayList<String>();

        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, trainInfo);//initializing the ArrayAdapter

        listView = (ListView)findViewById(R.id.train_listView);
        listView.setAdapter(adapter);//Linking the adapter      
        adapter.setNotifyOnChange(true);//This ensures that the changes in data so the UI components can refresh themselves     

        TrainData trainSchedule = new TrainData();
        trainSchedule.execute();
    }
    public class TrainData extends AsyncTask<Void,Void,Void>
    {
        ArrayList<String> nextTrains;

        protected void onPostExecute(Void arg0)//This method is called after the background process is complete 
        {
            adapter.clear();
            for(int i = 0;i<nextTrains.size();i++)
            {
                System.out.println(nextTrains.get(i));
                adapter.add(nextTrains.get(i));
            }
            adapter.add("Hello World");
            TextView updateMessage = (TextView) findViewById(R.id.train_list_info);
            updateMessage.setText("Here are the available trains for your trip from " + startStation + " to " + endStation);
            adapter.notifyDataSetChanged();//This send the signal that the data is changes and allows the UI components like the ListView to get updated.           

        }
        @Override
        protected Void doInBackground(Void... params) 
        {
            // TODO Auto-generated method stub
            try
            {
                String sURL = "http://www3.septa.org/hackathon/NextToArrive/"+ startStation + "/" + endStation + "/10"; 
                System.out.println(sURL);
                URL url = new URL(sURL);
                HttpURLConnection request = (HttpURLConnection) url.openConnection();
                request.connect();

                JsonParser jp = new JsonParser();//Json parsing tool
                JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent()));//Getting content in Json
                System.out.println("root:\n" + root);
                JsonArray rootArray = root.getAsJsonArray();

                nextTrains = new ArrayList<String>();
                if(rootArray.size() > 0)
                {
                    for(int i = 0;i<rootArray.size();i++)
                    {
                        JsonObject train = rootArray.get(i).getAsJsonObject();
                        String departureTime = train.get("orig_departure_time").getAsString();
                        String arrivalTime = train.get("orig_arrival_time").getAsString();
                        String delayTime = train.get("orig_delay").getAsString();
                        String trainNumber = train.get("orig_train").getAsString();

                        String result = "Train " + trainNumber + "\nDeparts from " + startStation + ": " + departureTime
                                        + "\nArrives at " + endStation + ": " + arrivalTime;
                        if(!delayTime.equals("On Time"))
                            result = result + "\nDelayed: " + delayTime;
                        nextTrains.add(result);
                    }
                }else
                {
                    nextTrains.add("No trains available from " + startStation + " to " + endStation);
                }


                }catch(Exception e)
                {
                    System.out.println("Unable to make http request!");
                }
            return null;
        }
        public void retrieveData()
        {

        }
    }
}

I would check that it is accessing the URL you think it is. `doInBackground` runs on a separate thread and then you are accessing field variables from the outer class to form the URL. You should, instead, pass those two variables in instead of using `` on the aSyncTask. That way, you know they will be the correct value in `doInBackground` — SDJMcHattie, Mar 01 '14 at 19:22
The thing is that the system.out.print prints out the correct url in the logcat. Hence, the url is correct. — user3213348, Mar 01 '14 at 19:29
OK, and what does `System.out.println("root:\n" + root);` output? — SDJMcHattie, Mar 01 '14 at 19:30
How about if you `System.out.println(request.getContent().toString())` just before you assign the `root`? I'm trying to establish which object isn't doing its job correctly. — SDJMcHattie, Mar 01 '14 at 19:52
yea the System.out.println(request.getContent().toString()) is blank also! — user3213348, Mar 01 '14 at 19:56
So it's the `HttpURLConnection` that's misbehaving. If you take the URL it is linking to by `println`ing the sURL and opening it in a browser, I take it you get data back? — SDJMcHattie, Mar 01 '14 at 19:58
I feel it has something to do with the FATAL Error in java.lang.string value — user3213348, Mar 01 '14 at 20:00
Where is that happening? I tried the URL out and it appears that http://www3.septa.org/hackathon/NextToArrive/Highland/Upsal/10 gives you results, whilst mis-spelling one of the stops gives you the empty [] that you're talking about. I'm guessing the sURL isn't exactly correct — SDJMcHattie, Mar 01 '14 at 20:05
yea SDJMcHattie is correct. The 30th Street Station spaces need to have %20. I was assuming that http would automatically put in the spaces, but it turns out it doesn't. — user3213348, Mar 01 '14 at 20:08
I've posted an answer to solve your underlying problem if you want to accept it. — SDJMcHattie, Mar 01 '14 at 20:11
See the update to the answer. I was mistaken in how it handles spaces — SDJMcHattie, Mar 01 '14 at 20:27
it still messes up the other parts of the url, like the '/' character — user3213348, Mar 01 '14 at 20:41
Wow, these URLEncoders really aren't helping are they? I've updated my answer again! — SDJMcHattie, Mar 01 '14 at 20:53
its fine, I used the uri only for the name of the station and then concatenated to the whole URL. — user3213348, Mar 01 '14 at 22:23

score 0 · Answer 1 · answered Mar 01 '14 at 19:27

0

You should avoid possible threading issues by defining the AsyncTask as <Intent, Void, Void> and call its execute method like trainSchedule.execute(getIntent()); Change doInBackground(Void... params) to doInBackground(Intent... params) and get the extras from that intent before you setup the URL by using

String start = params[0].getExtras().getString("fromStation");
String end = params[0].getExtras().getString("toStation");

answered Mar 01 '14 at 19:27

SDJMcHattie

1,690
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But the URL is correct when I do a print statement. – user3213348 Mar 01 '14 at 20:00

score 0 · Answer 2 · edited May 23 '17 at 12:20

0

Use the URLEncoder encode method to encode your URL which will change spaces to %20 and other necessary encoding

Update

As pointed out, the above method will actually encode spaces to + which is no good in this case because the server doesn't handle them well. You could also try Uri.encode which looks like it should encode spaces to %20 like you want.

Further Update

According to this answer you're going to have to encode the spaces yourself after using the URLEncoder like so: URLEncoder.encode(sURL, "UTF-8").replace("+", "%20")

edited May 23 '17 at 12:20

Community

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answered Mar 01 '14 at 20:11

SDJMcHattie

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FWIW, it will encode spaces as `+` with x-www-form-urlencoded encoding rules. – laalto Mar 01 '14 at 20:17
That's a really good point! I've added an additional bit of info to my answer – SDJMcHattie Mar 01 '14 at 20:24

score 0 · Answer 3 · answered Mar 01 '14 at 20:16

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run it as a java file. In the run it gives me a Fatal Error: Invalid Layout of java.lang.String at value

Run it as an Android application, not as a generic Java application.

answered Mar 01 '14 at 20:16

laalto

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Android not getting Json result

3 Answers3

Update

Further Update