Error with AsyncTask, what is the reason?

Question

Java

I want to display data from MySQL hosting to an Android application, but at startup the application crashes and an error occurs.
Main activity code:

import java.io.BufferedReader;
        import java.io.IOException;
        import java.io.InputStream;
        import java.io.InputStreamReader;
        import java.util.ArrayList;
        import java.util.HashMap;
        import java.util.List;
        import java.util.Map;

        import org.apache.http.HttpResponse;
        import org.apache.http.client.ClientProtocolException;
        import org.apache.http.client.HttpClient;
        import org.apache.http.client.methods.HttpPost;
        import org.apache.http.impl.client.DefaultHttpClient;
        import org.json.JSONArray;
        import org.json.JSONException;
        import org.json.JSONObject;

        import android.os.AsyncTask;
        import android.os.Bundle;
        import android.app.Activity;
        import android.view.Menu;
        import android.widget.ListView;
        import android.widget.SimpleAdapter;
        import android.widget.Toast;

public class MainActivity extends Activity {
    private String jsonResult;
    private String url = "http://cpriyankara.coolpage.biz/employee_details.php";
    private ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.listView1);
        accessWebService();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    // Async Task to access the web
    private class JsonReadTask extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... params) {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost(params[0]);
            try {
                HttpResponse response = httpclient.execute(httppost);
                jsonResult = inputStreamToString(
                        response.getEntity().getContent()).toString();
            }

            catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }

        private StringBuilder inputStreamToString(InputStream is) {
            String rLine = "";
            StringBuilder answer = new StringBuilder();
            BufferedReader rd = new BufferedReader(new InputStreamReader(is));

            try {
                while ((rLine = rd.readLine()) != null) {
                    answer.append(rLine);
                }
            }

            catch (IOException e) {
                // e.printStackTrace();
                Toast.makeText(getApplicationContext(),
                        "Error..." + e.toString(), Toast.LENGTH_LONG).show();
            }
            return answer;
        }

        @Override
        protected void onPostExecute(String result) {
            ListDrwaer();
        }
    }// end async task

    public void accessWebService() {
        JsonReadTask task = new JsonReadTask();
        // passes values for the urls string array
        task.execute(new String[] { url });
    }

    // build hash set for list view
    public void ListDrwaer() {
        List<Map<String, String>> employeeList = new ArrayList<Map<String, String>>();

        try {
            JSONObject jsonResponse = new JSONObject(jsonResult);
            JSONArray jsonMainNode = jsonResponse.optJSONArray("emp_info");

            for (int i = 0; i < jsonMainNode.length(); i++) {
                JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
                String name = jsonChildNode.optString("employee name");
                String number = jsonChildNode.optString("employee no");
                String outPut = name + "-" + number;
                employeeList.add(createEmployee("employees", outPut));
            }
        } catch (JSONException e) {
            Toast.makeText(getApplicationContext(), "Error" + e.toString(),
                    Toast.LENGTH_SHORT).show();
        }

        SimpleAdapter simpleAdapter = new SimpleAdapter(this, employeeList,
                android.R.layout.simple_list_item_1,
                new String[] { "employees" }, new int[] { android.R.id.text1 });
        listView.setAdapter(simpleAdapter);
        Toast.makeText(getApplication(), "c", Toast.LENGTH_SHORT).show();

    }

    private HashMap<String, String> createEmployee(String name, String number) {
        HashMap<String, String> employeeNameNo = new HashMap<String, String>();
        employeeNameNo.put(name, number);
        return employeeNameNo;
    }
}

And here is the listing of the error:

HostConnection::get() New Host Connection established 0xaff4a5f0, tid 19118
07-26 07:39:42.075 19118-19162/devbyte.grinvichkino E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
                                                                      Process: devbyte.grinvichkino, PID: 19118
                                                                      java.lang.RuntimeException: An error occurred while executing doInBackground()