What is this project?

This project implements a simple HTTPS server where users can register and then send/recieve information about sightseeing locations. The project was done as a programming course assignment so it is not really meant to be used for anything other than viewing/reference. The project deals with database programming (JDBC, SQLite), data formats (JSON, XML) and the server part of client-server applications as well as a little concurrency.

Code stuff

Registering a new user

When the server starts it creates an UserAuthenticator object which implements BasicAuthenticator. Then the server creates context for the different paths and sets the authenticator for them.RegistrationHandler is used for handling all requests to the /registration path. The handler implements HttpHandler.

@Override
public void handle(HttpExchange exchange) throws IOException {
     
  String responseString = null;
      
  if (exchange.getRequestMethod().equalsIgnoreCase("POST")) {
    
    if(checkContentType(exchange)){ // invalid Content-Type response handled inside checkContentType()
          InputStreamReader inputReader = new InputStreamReader(exchange.getRequestBody(), StandardCharsets.UTF_8);
          BufferedReader buffer = new BufferedReader(inputReader);
          String newUser = buffer.lines().collect(Collectors.joining("\n"));
          inputReader.close();

          if(newUser != null && newUser.length() != 0){
              JSONObject json = null;
              try {
                   json = new JSONObject(newUser);
              } catch(JSONException e) {
                  responseString = "JSON was faulty";
                  handleResponse(exchange, responseString, 400);
              }

              if(json != null){
                  tryToRegisterUser(exchange, json);
              }
          }
          else {
              responseString = "No user credentials provided";
              handleResponse(exchange, responseString, 400);
          }
      }
  }
  else {
      responseString = "Not supported; Only POST is accepted";
      handleResponse(exchange, responseString, 400);
  }
}           

In the above snippet the handler first checks the if the request is a "POST" request and then if it's Content-Type is valid by calling checkContentType() (is "application/json"). Then it reads the contents into newUser and attemps to create a JSONObject out of it. After this it calls the tryToRegisterUser() method which does some simple checks to ensure the new user has given all the required information. The tryToRegisterUser() method calls a method from the authenticator to try and add the user. he authenticator simply calls the database which does the final checks (user doesnt alreadye exists).

/**
* Tries to register the user from the given JSONObject. User can only be registered if the username is unique and password is not missing.
* @param exchange The HTTP request
* @param json The JSONObject containing user information
*/
private void tryToRegisterUser(HttpExchange exchange, JSONObject json) throws IOException {
      
    String responseString = null;
      
    try {
        if(json.getString("username").length() != 0 && json.getString("password").length() != 0){
            // Try to register the user
            if(authenticator.addUser(json.getString("username"), json.getString("password"), json.getString("email"), json.getString("userNickname"))){
                responseString = "Registration was succesful";
                handleResponse(exchange, responseString, 200);
            }
            else {
                responseString = "User already exists";
                handleResponse(exchange, responseString, 409);
            }
        }
        else {
            responseString = "Username or password is missing";
            handleResponse(exchange, responseString, 400);
        }

    } catch(JSONException e) {
        responseString = "JSON is missing a key";
        handleResponse(exchange, responseString, 400);
    }
}           

addUser() from the authenticator:

/**
* Attempts to add a new user with given parameters.
* @param username The name used for registering/login
* @param password
* @param email
* @param nickname The name shown publicly
* @return True if the user could be added. False if the user could not be added.
*/
public boolean addUser(String username, String password, String email, String nickname) {

    JSONObject potentialUser = new User(username, password, email, nickname).toJsonObject();
    try {
        return db.insertUser(potentialUser);
    } 
    catch(SQLException e) {
        System.out.println("adding user to database failed");
        e.printStackTrace();
        return false;
    }
}           

And inside the database: (check if user already exists, if not add user)

/**
* Creates a new user in the database if the provided user does not already exist.
* @param user
* @throws SQLException
* @return True if the user could be added, False if not.
*/
public boolean insertUser(JSONObject user) throws SQLException {

    if(checkIfUserExists(user.getString("username"))){
        return false;
    }

    PreparedStatement prepUser = dbConnection.prepareStatement(preparedInsertUser);
    prepUser.setString(1, user.getString("username"));
    prepUser.setString(2, encryptPassword(user.getString("password")));
    prepUser.setString(3, user.getString("email"));
    prepUser.setString(4, user.getString("userNickname"));
    prepUser.executeUpdate();
    prepUser.close();

    return true;
}         

/**
* Checks if the provided username is already in the database.
* @param username
* @throws SQLException
* @return True if the username is taken, false if the username is not taken.
*/
private boolean checkIfUserExists(String username) throws SQLException {
      
    String preparedUserSelect = "SELECT username FROM users WHERE username = ?";
    PreparedStatement prep = dbConnection.prepareStatement(preparedUserSelect);
    prep.setString(1, username);
    ResultSet result = prep.executeQuery();

    return result.next();
}