application Android Json Mysql : Error in http connection android.os.NetworkOnMainThreadException

Question

When I start my emulator after install the application it return me error log this is error they're return me

error opening trace file: No such file or directory (2)
1.Error in http connection android.os.NetworkOnMainThreadException
2.Error converting result java.lang.NullPointerException: lock == null
3.Error parsing data org.json.JSONException: End of input at character 0 

this is my code java

package com.example.locav;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class Locav extends Activity {
    TextView txt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.accueil);
     txt=(TextView)findViewById(R.id.text1);
     txt.setText("Connexion...");
     txt.setText(getServerData(strURL)); 

    }
    public static final String strURL ="http://105.143.142.224/locav/consulte.php";
    private String getServerData(String returnString) {
        InputStream is = null;
        String result = "";
        // Envoyer la requête au script PHP.
        // Script PHP : $sql=mysql_query("select * from tblVille where Nom_ville like '".$_REQUEST['ville']."%'");
        // $_REQUEST['ville'] sera remplacé par L dans notre exemple.
        // Ce qui veut dire que la requête enverra les marques commençant par la lettre f
        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
        nameValuePairs.add(new BasicNameValuePair("marque","f"));

        // Envoie de la commande http
        try{
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost(strURL);
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();

        }catch(Exception e){
            Log.e("log_tag", "1.Error in http connection " + e.toString());
        }

        // Convertion de la requête en string
        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");
            }
            is.close();
            result=sb.toString();
        }catch(Exception e){
            Log.e("log_tag", "2.Error converting result " + e.toString());
        }
        // Parse les données JSON
        try{
            JSONArray jArray = new JSONArray(result);
            for(int i=0;i<jArray.length();i++){
                JSONObject json_data = jArray.getJSONObject(i);
                // Affichage ID_ville et Nom_ville dans le LogCat
                Log.i("log_tag","idReservation: "+json_data.getInt("idReservation")+
                        ", marque: "+json_data.getString("marque")
                );
                // Résultats de la requête
                returnString += "\n\t" + jArray.getJSONObject(i); 
            }
        }catch(JSONException e){
            Log.e("log_tag", "3.Error parsing data " + e.toString());
        }
        return returnString; 
    }
}

this code is completed with a manisfest and layout

Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.locav"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />
    <uses-permission android:name="android.permission.INTERNET"/>


    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.locav.Locav"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

and my code php

<?php
  mysql_connect("localhost","root","");
  mysql_select_db("bdlocav");
  $sql=mysql_query("select * from tbreservation where marque like '".$_REQUEST['marque']."%'");
  while($row=mysql_fetch_assoc($sql))
  $output[]=$row;
  print(json_encode($output));
  mysql_close();
?>

Answer 1

The Exception is really clearly, see the docs:

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

So you are doing a network request on the MainThread. This happens because yo do this in the MainActivity, which is executed on the MainThread.

Simply use an AsyncTask or a BackgroundService for such things to get around this.

class DownloadTask extends AsyncTask<String, Void, String> {

    protected String doInBackground(String... urls) {
        //Put your getServerData-logic here
        //return serverData

    }
    //This Method is called when Network-Request finished
    protected void onPostExecute(String serverData) {
        textView.setText(serverData)
    }
}

In your Activity run the AsyncTask like this:

DownloadTask dlTask = new DownloadTask();
dlTask.execute()