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 * and open the template in the editor.
 */
package AndroidControllers;

import Database.Authentication;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.json.simple.JSONObject;

/**
 *
 * @author serge
 */
public class Android extends HttpServlet {

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {
            /* TODO output your page here. You may use following sample code. */
            out.println("<!DOCTYPE html>");
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet Android</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet Android at " + request.getContextPath() + "</h1>");
            out.println("</body>");
            out.println("</html>");
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("application/json");
        response.setCharacterEncoding("utf-8");
            PrintWriter writer = response.getWriter();
            String user = request.getParameter("username");
            String pass = request.getParameter("password");
            PrintWriter out = response.getWriter();
            JSONObject logged = Authentication.login_json(user, pass);
            if(logged != null)
                writer.print(logged);
            else{
                logged.put("type", "ERROR");
                logged.put("username", "ERROR");
                writer.print(logged);
            }
        //processRequest(request, response);
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {


        processRequest(request, response);

    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}

public static JSONObject login_json(String user, String pass){
        JSONObject json = new JSONObject();
        Connection conn = null;
        String sql = "select username, user_type from users where username = '" + user +
                "' and password = '" + pass + "';";
        try{
            Class.forName("com.mysql.jdbc.Driver");
            conn = Utilities.connect();
            Statement st = conn.createStatement();
            ResultSet rs = st.executeQuery(sql);
            if(rs.next()){
                json.put("username", user);
                json.put("type", rs.getString("user_type"));
            }
            else{
                json.put("username", "FAIL");
                json.put("type", "FAIL");
            }
        }
        catch(SQLException | ClassNotFoundException ecc){
            System.out.println("ERROR: " + ecc.getMessage());
        }
        finally{
            Utilities.disconnect(conn);
        }
        return json;
    }

package com.example.serge.biblioteca;
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
public class http_authentication{
    public static JSONObject login_json(String user, String pass) {
        String json_string = "";
        JSONObject stream = new JSONObject();
        JSONParser parser = new JSONParser();
        String url = "http://localhost:43746/Progetto_TWEB/Android?username=" + user
                + "&password=" + pass;
        try {
            URL link = new URL(url);
            HttpURLConnection urlConnection = (HttpURLConnection) link.openConnection();

            // Check the connection status
            if (urlConnection.getResponseCode() == 200) {
                // if response code = 200 ok
                InputStream in = new BufferedInputStream(urlConnection.getInputStream());

                // Read the BufferedInputStream
                BufferedReader r = new BufferedReader(new InputStreamReader(in));
                StringBuilder sb = new StringBuilder();
                String line;
                while ((line = r.readLine()) != null) {
                    sb.append(line);
                }
                json_string = sb.toString();
                stream = (JSONObject) parser.parse(json_string);

                // End reading...............
                // Disconnect the HttpURLConnection
                urlConnection.disconnect();
            } else {
                // Do something
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } finally {

        }
        // Return the data from specified url
        return stream;
    }
}

package com.example.serge.biblioteca;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import org.json.simple.parser.JSONParser;

import org.json.simple.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

/**
 * Created by serge on 28/12/2017.
 */

public class login extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        final Button login = (Button) findViewById(R.id.login_login);
        final EditText username = (EditText) findViewById(R.id.txtUser);
        final EditText password = (EditText) findViewById(R.id.txtPass);


        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

        JSONObject logged = new JSONObject();
        boolean vuoto = false;
        String logged_type = "";
        String logged_user = "", user_type = "";
        TextView welcome = (TextView)findViewById(R.id.normal_intro);
        String user = username.getText().toString();
        String pass = password.getText().toString();
        try {
            logged = http_authentication.login_json(user, pass);
                vuoto = logged.isEmpty();
//The following setText always returns an empty String so I think the object is null
                username.setText(logged.toString());
        }
        catch(Exception ecc){
            username.setText(ecc.getMessage());
        }
            }
        });
    }
}