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From Spring Boot to Nexy

Nexy's modular router keeps the shape of a Spring Boot app: a @RestController is a @Controller class, a @Service is an @Injectable injected through __init__, and a module groups them. Bean Validation becomes Pydantic, and springdoc's OpenAPI page is built in.

Each section below shows a Spring Boot habit, then the same thing in Nexy.

Turning the modular router on

DemoApplication.java
@SpringBootApplicationpublic class DemoApplication {    public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); }}

The root module is a field of nexyconfig.py, and nx dev serves it:

nexyconfig.py
from nexy.core.models import NexyConfigModel from src.apps.app_module import AppModule  class NexyConfig(NexyConfigModel):    useRouter = AppModule

Spring finds its beans by scanning packages; a Nexy module lists them, so what a module serves is written in one place.

A controller

HelloController.java
@RestController@RequestMapping("/api/hello")public class HelloController {    @GetMapping    public Map<String, String> hello() {        return Map.of("message", "Hello");    }}

The path is the first argument of @Controller, and the method name is the HTTP verb:

src/apps/hello/hello_controller.py
from nexy.decorators import Controller  @Controller("/api/hello")class HelloController:    async def get(self) -> dict:        return {"message": "Hello"}

A controller has one handler per verb, so @GetMapping and @PostMapping on one path are the get and post methods of one class. GET /items and GET /items/{id} are two controllers.

@PathVariable and @RequestParam

UserController.java
@GetMapping("/api/users/{id}")public Map<String, Object> user(@PathVariable long id,                                @RequestParam(defaultValue = "") String fields) {    return Map.of("id", id, "fields", fields);}

{id} stays in the path and becomes a typed parameter; a request parameter is a parameter with a default:

src/apps/users/user_controller.py
from nexy.decorators import Controller  @Controller("/api/users/{id}")class UserController:    async def get(self, id: int, fields: str = "") -> dict:        return {"id": id, "fields": fields}

A non-numeric id answers 404, and a request parameter of the wrong type 422.

@RequestBody, @Valid and ResponseEntity

NewItem.java
public record NewItem(@NotBlank @Size(max = 100) String name,                      @Positive double price) {}
ItemController.java
@PostMapping("/api/items")public ResponseEntity<NewItem> create(@Valid @RequestBody NewItem item) {    return ResponseEntity.status(HttpStatus.CREATED).body(item);}

The record and its annotations are a Pydantic model, always validated, and @UseResponse sets the status:

src/apps/items/items_controller.py
from pydantic import BaseModel, Field from nexy.decorators import Controller, UseResponse  class NewItem(BaseModel):    name: str = Field(min_length=1, max_length=100)    price: float = Field(gt=0)  @Controller("/api/items")class ItemsController:    @UseResponse(status_code=201)    async def post(self, item: NewItem) -> NewItem:        return item

@Service and constructor injection

GreetingService.java
@Servicepublic class GreetingService {    public String greet(String name) { return "Hello " + name; }} @RestController@RequestMapping("/api/greet")public class GreetingController {    private final GreetingService greetings;     public GreetingController(GreetingService greetings) { this.greetings = greetings; }     @GetMapping    public Map<String, String> greet(@RequestParam String name) {        return Map.of("message", greetings.greet(name));    }}

@Service is @Injectable(), and the annotation of __init__ tells the container what to inject:

src/apps/greet/greeting_service.py
from nexy.decorators import Injectable  @Injectable()class GreetingService:    def greet(self, name: str) -> str:        return f"Hello {name}"
src/apps/greet/greeting_controller.py
from nexy.decorators import Controller from .greeting_service import GreetingService  @Controller("/api/greet")class GreetingController:    def __init__(self, greetings: GreetingService) -> None:        self.greetings = greetings     async def get(self, name: str) -> dict:        return {"message": self.greetings.greet(name)}

A bean is a singleton by default, as in Spring. @RequestScope is @Injectable(scope=Scope.REQUEST), and @Scope("prototype") is Scope.TRANSIENT. See Dependency injection.

@Configuration classes and modules

A module lists its controllers and the services they use, and exports what other modules may inject:

src/apps/greet/greet_module.py
from nexy.decorators import Module from .greeting_controller import GreetingControllerfrom .greeting_service import GreetingService  @Module()class GreetModule:    controllers = [GreetingController]    providers = [GreetingService]    exports = [GreetingService]

The root module imports the others:

src/apps/app_module.py
from nexy.decorators import Module from .admin.admin_module import AdminModulefrom .greet.greet_module import GreetModulefrom .health_controller import PublicHealthControllerfrom .hello.hello_controller import HelloControllerfrom .items.items_controller import ItemsControllerfrom .orders.orders_controller import OrderControllerfrom .posts.posts_module import PostsModulefrom .signup.signup_controller import SignupControllerfrom .users.user_controller import UserControllerfrom .users.users_page_controller import UsersPageControllerfrom .ws.echo_controller import EchoController  @Module()class AppModule:    controllers = [        HelloController,        UserController,        ItemsController,        OrderController,        SignupController,        PublicHealthController,        UsersPageController,        EchoController,    ]    imports = [GreetModule, AdminModule, PostsModule]

@RequestMapping on the class

AdminController.java
@RestController@RequestMapping("/admin")public class AdminController {    @GetMapping("/stats")    public Map<String, Integer> stats() { return Map.of("users", 3); }     @GetMapping("/health")    public Map<String, String> health() { return Map.of("status", "UP"); }}

A shared mapping is the prefix of a module, and each sub-path is a controller of that module:

src/apps/admin/admin_controllers.py
from nexy.decorators import Controller, UseGuard from .guards import require_admin  @Controller("/stats")@UseGuard(require_admin)class StatsController:    async def get(self) -> dict:        return {"users": 3}  @Controller("/health")@UseGuard(require_admin)class HealthController:    async def get(self) -> dict:        return {"status": "UP"}
src/apps/admin/admin_module.py
from nexy.decorators import Module from .admin_controllers import HealthController, StatsController  @Module(prefix="/admin")class AdminModule:    controllers = [StatsController, HealthController]

Spring Security

SecurityConfig.java
@BeanSecurityFilterChain filters(HttpSecurity http) throws Exception {    return http.authorizeHttpRequests(auth -> auth            .requestMatchers("/admin/**").hasRole("ADMIN")            .anyRequest().permitAll())        .build();}

A guard is a function that raises when the request may not go on. @UseGuard puts it on a controller, or on one method, like @PreAuthorize:

src/apps/admin/guards.py
from nexy.http import Header, HTTPException  def require_admin(x_role: str = Header("")) -> None:    if x_role != "admin":        raise HTTPException(status_code=403, detail="Admins only")

Filters

AppHeaderFilter.java
@Componentpublic class AppHeaderFilter extends OncePerRequestFilter {    @Override    protected void doFilterInternal(HttpServletRequest req, HttpServletResponse res,                                    FilterChain chain) throws ServletException, IOException {        res.setHeader("X-App", "demo");        chain.doFilter(req, res);    }}

A filter for every request is an ASGI middleware class, listed in nexyconfig.py:

src/middlewares/app_header.py
from starlette.middleware.base import BaseHTTPMiddleware  class AppHeader(BaseHTTPMiddleware):    async def dispatch(self, request, call_next):        response = await call_next(request)        response.headers["x-app"] = "demo"        return response
nexyconfig.py
from nexy.core.models import NexyConfigModel from src.apps.app_module import AppModulefrom src.middlewares.app_header import AppHeader  class NexyConfig(NexyConfigModel):    useRouter = AppModule    useMiddlewares = [(AppHeader, {})]

A HandlerInterceptor that only runs before some controllers is a guard on them.

ResponseStatusException and @ControllerAdvice

OrderController.java
@GetMapping("/api/orders/{id}")public Order order(@PathVariable long id) {    return orders.findById(id)        .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "No such order"));}
src/apps/orders/orders_controller.py
from nexy.decorators import Controllerfrom nexy.http import HTTPException ORDERS = {1: {"id": 1, "total": 42}}  @Controller("/api/orders/{id}")class OrderController:    async def get(self, id: int) -> dict:        if id not in ORDERS:            raise HTTPException(status_code=404, detail="No such order")        return ORDERS[id]

An API client that sends Accept: application/json gets {"detail": "No such order"} with the status you raised; a browser gets the HTML not-found page.

Thymeleaf

UserPageController.java
@Controllerpublic class UserPageController {    @GetMapping("/users")    public String users(Model model) {        model.addAttribute("users", List.of(new User("Ada"), new User("Alan")));        return "users";    }}
templates/users.html
<ul>  <li th:each="user : ${users}" th:text="${user.name}"></li></ul>

A controller returns a view the way it returns "users": useViews renders a .nexy file, and its context is the Model:

src/apps/users/users_view.nexy
---users: prop[list]---<ul>  {% for user in users %}  <li>{{ user.name | e }}</li>  {% endfor %}</ul>
src/apps/users/users_page_controller.py
from nexy import useViewsfrom nexy.decorators import Controller  @Controller("/users")class UsersPageController:    async def get(self):        users = [{"name": "Ada"}, {"name": "Alan"}]        return useViews("src/apps/users/users_view.nexy", context={"users": users})

th:text escapes and {{ }} does not: escape what a visitor typed with | e. A page can also stay a file of src/routes/, served next to the controllers.

JPA entities and repositories

Post.java
@Entitypublic class Post {    @Id @GeneratedValue Long id;    String title;    boolean published;} public interface PostRepository extends JpaRepository<Post, Long> {    List<Post> findByPublishedTrue();}

The entity is a SQLModel class, and the repository an injectable service around a session:

src/models/post_model.py
from sqlmodel import Field, SQLModel  class Post(SQLModel, table=True):    id: int | None = Field(default=None, primary_key=True)    title: str    published: bool = False
src/apps/posts/post_repository.py
from sqlmodel import Session, select from nexy.decorators import Injectablefrom src.configs.db import enginefrom src.models.post_model import Post  @Injectable()class PostRepository:    def find_by_published_true(self) -> list[Post]:        with Session(engine) as session:            return list(session.exec(select(Post).where(Post.published)))
src/apps/posts/posts_controller.py
from nexy.decorators import Controller from .post_repository import PostRepository  @Controller("/api/posts/published")class PublishedPostsController:    def __init__(self, posts: PostRepository) -> None:        self.posts = posts     async def get(self) -> dict:        return {"titles": [post.title for post in self.posts.find_by_published_true()]}
src/apps/posts/posts_module.py
from nexy.decorators import Module from .post_repository import PostRepositoryfrom .posts_controller import PublishedPostsController  @Module()class PostsModule:    controllers = [PublishedPostsController]    providers = [PostRepository]

Flyway or Liquibase migrations become nx migrate -m "add posts" and nx migrate --upgrade. See Databases.

application.properties

Spring Boot Nexy
server.port=8080 usePort = 8080 in nexyconfig.py
spring.datasource.url DATABASE_URL in .env
@CrossOrigin / CorsConfigurationSource useCORS = {"allow_origins": [...]}
server.compression.enabled=true useGZip = {"minimum_size": 1000}
springdoc.swagger-ui.path=/docs useDocsUrl = "/docs", on by default
src/main/resources/static/ public/, served at /
nexyconfig.py
from nexy.core.models import NexyConfigModel from src.apps.app_module import AppModule  class NexyConfig(NexyConfigModel):    useRouter = AppModule    usePort = 8080    useCORS = {"allow_origins": ["https://example.com"]}    useGZip = {"minimum_size": 1000}

Actuator health

application.properties
management.endpoints.web.exposure.include=health

A health check is a controller like any other, here the /admin/health one above. A public one goes in the root module:

src/apps/health_controller.py
from nexy.decorators import Controller  @Controller("/health")class PublicHealthController:    async def get(self) -> dict:        return {"status": "UP"}

@Async and @Scheduled

MailService.java
@Asyncpublic void sendWelcome(String email) { ... }

Work that runs after the answer is a background task, taken as a parameter:

src/apps/signup/signup_controller.py
from nexy.decorators import Controller, UseResponsefrom nexy.http import BackgroundTasks  def send_welcome(email: str) -> None: ...  @Controller("/api/signup")class SignupController:    @UseResponse(status_code=202)    async def post(self, email: str, tasks: BackgroundTasks) -> dict:        tasks.add_task(send_welcome, email)        return {"queued": True}

For @Scheduled jobs, run a scheduler such as APScheduler, or a cron job, next to nx start.

WebSockets

EchoHandler.java
public class EchoHandler extends TextWebSocketHandler {    @Override    protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {        session.sendMessage(message);    }}

A socket method opens a WebSocket on the path of its controller:

src/apps/ws/echo_controller.py
from fastapi import WebSocket from nexy.decorators import Controller  @Controller("/ws/echo")class EchoController:    async def socket(self, websocket: WebSocket) -> None:        await websocket.accept()        await websocket.send_text(await websocket.receive_text())

Clients connect to /ws/echo/, with the trailing slash.

Tests with MockMvc

HelloControllerTest.java
@WebMvcTest(HelloController.class)class HelloControllerTest {    @Autowired MockMvc mvc;     @Test    void hello() throws Exception {        mvc.perform(get("/api/hello")).andExpect(jsonPath("$.message").value("Hello"));    }}
tests/test_hello.py
from fastapi.testclient import TestClient from nexy.app import app  def test_hello():    assert TestClient(app).get("/api/hello").json() == {"message": "Hello"}

Running

Spring Boot Nexy
start.spring.io nx new, with the modular router
./mvnw spring-boot:run with DevTools nx dev
./mvnw package && java -jar app.jar nx build, then nx start
./mvnw test nx test

Next steps

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