Android登录不起作用

Question

I try to learn android programming on the internet but when I want to create a login system it just doesn't write "Succes". My php file:

<?php
$con = mysqli_connect("hostname", "username", "password", "database");

$email = $_POST['email'];
$password = $_POST['password'];

$query = mysqli_query($con, "SELECT id FROM users WHERE email like '$email' and password like '$password'");
if(mysqli_num_rows($query) > 0){
echo "Success!";
} else {
echo "Wrong e-mail or password!";
}
mysqli_close($con);
?>

and I also got 2 java class, the first is the MainActivity:

public class MainActivity extends AppCompatActivity {

    EditText email, password;
    //Button loginbtn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        email = (EditText) findViewById(R.id.editText2);
        password = (EditText) findViewById(R.id.editText3);
    }

    public void onLogin(View view){
        String Email = email.getText().toString();
        String Password = password.getText().toString();
        String type = "login";

        BackgroundWorker backgroundWorker = new BackgroundWorker(this);
        backgroundWorker.execute(Email, Password, type);
    }
}

and the second is my backgroundWorker:

public class BackgroundWorker extends AsyncTask<String,Void,String> {
    Context context;
    AlertDialog alertDialog;
    BackgroundWorker (Context cdx){
        context = cdx;
    }
    @Override
    protected String doInBackground(String... params){
        String type = params[0];
        String login_url = "http://diamondearth.16mb.com/android/login.php";
        if(type.equals("login")){
            try {
                String email = params[1];
                String password = params[2];
                URL url = new URL(login_url);
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);
                OutputStream outputStream = httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
                String post_data = URLEncoder.encode("email","UTF-8")+"="+URLEncoder.encode(email,"UTF-8")+"&"
                        +URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(password,"UTF-8");
                bufferedWriter.write(post_data);
                bufferedWriter.flush();
                bufferedWriter.close();
                outputStream.close();
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "iso-8859-1"));
                String result="";
                String line="";
                while((line = bufferedReader.readLine())!= null){
                    result += line;
                }
                bufferedReader.close();
                inputStream.close();
                httpURLConnection.disconnect();
            } catch (MalformedURLException e){
                e.printStackTrace();
            } catch (IOException e){
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override
    protected  void onPreExecute(){
        alertDialog = new AlertDialog.Builder(context).create();
        alertDialog.setTitle("Login Status");
    }

    @Override
    protected  void onPostExecute(String result){
        alertDialog.setMessage(result);
        alertDialog.show();
    }
}