spring-boot-rest/libraries-http/src/main/java/com/baeldung/javalin/User/UserController.java

package com.baeldung.javalin.User;

import io.javalin.Handler;

import java.util.Objects;

public class UserController {
    public static Handler fetchAllUsernames = ctx -> {
        UserDao dao = UserDao.instance();
        Iterable<String> allUsers = dao.getAllUsernames();
        ctx.json(allUsers);
    };

    public static Handler fetchById = ctx -> {
        int id = Integer.parseInt(Objects.requireNonNull(ctx.param("id")));
        UserDao dao = UserDao.instance();
        User user = dao.getUserById(id).get();
        if (user == null) {
            ctx.html("Not Found");
        } else {
            ctx.json(user);
        }
    };
}