Single-file Spring Boot application. A silly example but it can be done. Run it as `jbang TodoApp.java`. You need the https://www.jbang.dev/ tool installed

TodoApp.java

//JAVA 17
//DEPS org.springframework.boot:spring-boot-dependencies:3.1.3@pom
//DEPS org.springframework.boot:spring-boot-starter-web
//DEPS org.springframework.boot:spring-boot-starter-data-jdbc
//DEPS com.h2database:h2

package app;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.event.EventListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.data.annotation.Id;
import org.springframework.data.jdbc.repository.query.Modifying;
import org.springframework.data.jdbc.repository.query.Query;
import org.springframework.data.relational.core.mapping.Table;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Repository;
import org.springframework.web.bind.annotation.*;

@SpringBootApplication
@RestController
public class TodoApp {
    public static void main(String[] args) {
        SpringApplication.run(TodoApp.class, args);
    }
    private final Logger logger = LoggerFactory.getLogger(TodoApp.class);

    private final TodoRepository todoRepository;

    TodoApp(TodoRepository todoRepository) {
        this.todoRepository = todoRepository;
    }

    @GetMapping("/todos")
    Iterable<Todo> todos() {
        return todoRepository.findAll();
    }

    @PostMapping("/todos")
    Todo newTodo(@RequestBody TodoCreateCommand todo) {
        logger.debug("Creating new todo: {}", todo);
        return todoRepository.save(new Todo(null, todo.description(), todo.done()));
    }

    @PostMapping("/todos/{id}/done")
    Todo markTodoDone(@PathVariable("id") Integer id) {
        todoRepository.markAsDone(id);
        return todoRepository.findById(id).orElseThrow();
    }

    @PostMapping("/todos/{id}/not-done")
    Todo markTodoNotDone(@PathVariable("id") Integer id) {
        todoRepository.markAsNotDone(id);
        return todoRepository.findById(id).orElseThrow();
    }
}

@Component
record StartupAppListener(JdbcTemplate jdbc) {
    @EventListener
    public void onApplicationEvent(ContextRefreshedEvent event) {
        jdbc.execute("""
            CREATE TABLE IF NOT EXISTS todos
            (
                id          INTEGER PRIMARY KEY NOT NULL AUTO_INCREMENT,
                description TEXT                NOT NULL,
                done        BOOLEAN             NOT NULL DEFAULT 0
            );
        """);
    }
}

record TodoCreateCommand(String description, Boolean done) {
}

@Table("TODOS")
record Todo(@Id Integer id, String description, Boolean done) {
}

@Repository
interface TodoRepository extends CrudRepository<Todo, Integer> {

    @Modifying
    @Query("update todos set done = true where id=:id")
    void markAsDone(@Param("id") Integer id);

    @Modifying
    @Query("update todos set done = false where id=:id")
    void markAsNotDone(@Param("id") Integer id);
}