client-side-views

name	client-side-views
description	Guide Claude on building client-side (React/Hilla) views in Vaadin 25. This skill should be used when the user asks to "build a client-side view", "create a React view", "use Hilla", "use @BrowserCallable", "file-based routing", "call Java from React", "create an offline view", "client-side rendering", "use ViewConfig", "create a Hilla endpoint", "use reactive endpoints", "subscribe to server push from React", "use signals in React", or needs help with React-based Vaadin views, file-based routing conventions, or type-safe backend communication.
version	0.1.0

Client-Side Views with React and Hilla in Vaadin 25

Use the Vaadin MCP tools (search_vaadin_docs) to look up the latest documentation whenever uncertain about a specific API detail. Always set vaadin_version to "25" and ui_language to "react".

When to Use Client-Side Views

Client-side (React/Hilla) views run in the browser and communicate with Java endpoints over HTTP. Choose them when:

• High traffic — no server-side UI state per user, so the server scales better
• Offline support — views can work without a server connection
• Fine-grained DOM control — full access to the React ecosystem and browser APIs
• Rich interactivity — complex animations, drag-and-drop, or canvas rendering

Use server-side Flow views when you need rapid prototyping with pure Java, direct database access from UI code, or full server-side security for every interaction.

A single Vaadin 25 application can mix both models — Flow views and Hilla views coexist via the generated routes.tsx.

Project Structure

src/main/frontend/
  views/                     # File-based routing root
    @layout.tsx              # Main application layout
    @index.tsx               # Root view (/)
    about.tsx                # /about
    products/
      @index.tsx             # /products
      {productId}.tsx        # /products/:productId
  components/                # Shared React components (not routes)
  generated/                 # Auto-generated endpoint clients (do not edit)
    endpoints.ts

src/main/java/
  com/example/services/
    ProductService.java      # @BrowserCallable endpoint

The generated/ directory is rebuilt automatically during development. Import generated endpoint clients from Frontend/generated/endpoints.

File-Based Routing

Views are .tsx files in src/main/frontend/views/. The file path determines the URL.

Filename Conventions

File	URL	Purpose
@index.tsx	Directory index (/)	Landing page for a directory
@layout.tsx	—	Wrapping layout with <Outlet/>
about.tsx	/about	Static route
{productId}.tsx	/products/:productId	Required parameter
{{search}}.tsx	/search/:search?	Optional parameter
{...wildcard}.tsx	/*	Wildcard (catch-all)
_utils.tsx	—	Ignored by router (underscore prefix)

Route Parameters

Access parameters with React Router's useParams:

import { useParams } from 'react-router';

export default function ProductView() {
  const { productId } = useParams();
  // fetch product by productId...
}

Programmatic Navigation

import { useNavigate } from 'react-router';

function SaveButton() {
  const navigate = useNavigate();

  const handleSave = async () => {
    await ProductService.save(product);
    navigate('/products');
  };

  return <Button onClick={handleSave}>Save</Button>;
}

ViewConfig

Export a config object from any view to customize its route metadata:

import type { ViewConfig } from '@vaadin/hilla-file-router/types.js';

export default function DashboardView() {
  return <div>Dashboard content</div>;
}

export const config: ViewConfig = {
  title: 'Dashboard',
  loginRequired: true,
  rolesAllowed: ['ADMIN', 'MANAGER'],
  menu: {
    title: 'Dashboard',
    icon: 'vaadin:dashboard',
    order: 1,
  },
};

Key properties: title, route, loginRequired, rolesAllowed, skipLayouts, menu (title, icon, order, exclude), detail. See the reference file for the full property table.

Auto-Generated Menu

Use createMenuItems() from @vaadin/hilla-file-router/runtime.js to populate navigation:

import { createMenuItems } from '@vaadin/hilla-file-router/runtime.js';
import { SideNavItem } from '@vaadin/react-components/SideNavItem.js';
import { Icon } from '@vaadin/react-components/Icon.js';

{createMenuItems().map(({ to, icon, title }) => (
  <SideNavItem path={to} key={to}>
    {icon && <Icon icon={icon} slot="prefix" />}
    {title}
  </SideNavItem>
))}

Layouts

Create @layout.tsx in any directory. It wraps sibling and child views via <Outlet/>. Use AppLayout with SideNav for the standard application shell:

import { AppLayout } from '@vaadin/react-components/AppLayout.js';
import { DrawerToggle } from '@vaadin/react-components/DrawerToggle.js';
import { Suspense } from 'react';
import { Outlet } from 'react-router';

export default function MainLayout() {
  return (
    <AppLayout primarySection="drawer">
      <div slot="drawer" className="flex flex-col justify-between h-full p-m">
        <h1 className="text-l m-0">My App</h1>
        {/* SideNav with createMenuItems() here */}
      </div>
      <DrawerToggle slot="navbar" aria-label="Menu toggle" />
      <Suspense fallback={<div>Loading...</div>}>
        <Outlet />
      </Suspense>
    </AppLayout>
  );
}

Set skipLayouts: true in ViewConfig to render a view without parent layouts (e.g., login page).

@BrowserCallable Endpoints

Annotate a Java service with @BrowserCallable to expose it to the frontend. Hilla generates type-safe TypeScript clients automatically.

Java Service

@BrowserCallable
@AnonymousAllowed
public class ProductService {
    private final ProductRepository repo;

    public ProductService(ProductRepository repo) {
        this.repo = repo;
    }

    @RolesAllowed("ADMIN")
    public Product save(@Valid @Nonnull Product product) {
        return repo.save(product);
    }

    public @Nonnull List<@Nonnull Product> findAll() {
        return repo.findAll();
    }
}

Calling from React

import { ProductService } from 'Frontend/generated/endpoints';
import { useEffect } from 'react';
import { useSignal } from '@vaadin/hilla-react-signals';
import type Product from 'Frontend/generated/com/example/Product';

export default function ProductListView() {
  const products = useSignal<Product[]>([]);

  useEffect(() => {
    ProductService.findAll().then(data => {
      products.value = data;
    });
  }, []);

  return (
    <ul>
      {products.value.map(p => (
        <li key={p.id}>{p.name}</li>
      ))}
    </ul>
  );
}

Security Annotations

Every @BrowserCallable method is denied by default. Add one of:

Annotation	Access
@AnonymousAllowed	Anyone, no login required
@PermitAll	Any authenticated user
@RolesAllowed("ROLE")	Users with the specified role(s)
@DenyAll	Explicitly blocked (the default)

Place on the class for a default, or on individual methods to override.

Error Handling

Catch EndpointValidationError (Bean Validation failures with per-field validationErrorData), EndpointError (server exceptions with message and type), or plain errors (network failures). All from @vaadin/hilla-frontend. See the reference file for a complete error handling template.

Reactive Endpoints (Server Push)

Return a Flux from a @BrowserCallable method to push data to the browser:

Java Service

@BrowserCallable
public class TimeService {

    @AnonymousAllowed
    public Flux<@Nonnull String> getClock() {
        return Flux.interval(Duration.ofSeconds(1))
                .onBackpressureDrop()
                .map(i -> Instant.now().toString());
    }

    @AnonymousAllowed
    public EndpointSubscription<@Nonnull String> getClockCancellable() {
        return EndpointSubscription.of(getClock(), () -> {
            // cleanup when client unsubscribes
        });
    }
}

Subscribing from React

import { TimeService } from 'Frontend/generated/endpoints';
import type { Subscription } from '@vaadin/hilla-frontend';

const sub = useSignal<Subscription<string> | undefined>(undefined);

// Start
sub.value = TimeService.getClockCancellable()
  .onNext(time => { serverTime.value = time; })
  .onError(err => console.error(err));

// Stop
sub.value?.cancel();
sub.value = undefined;

The Subscription object provides cancel(), onNext(), onError(), onComplete(), and onSubscriptionLost() callbacks. See the reference file for the full API table.

Signals in React

Vaadin provides useSignal as a lightweight alternative to React's useState. Signals skip unnecessary re-renders by updating only the DOM nodes that read the signal value.

import { useSignal, useComputed } from '@vaadin/hilla-react-signals';

export default function CounterView() {
  const count = useSignal(0);
  const doubled = useComputed(() => count.value * 2);

  return (
    <div>
      <p>Count: {count.value}</p>
      <p>Doubled: {doubled.value}</p>
      <Button onClick={() => count.value++}>Increment</Button>
    </div>
  );
}

• Read/write via .value
• useComputed creates derived signals that update automatically
• Signals work with Vaadin components the same way as with plain HTML elements

Best Practices

1. Choose the right model — use client-side views for high-traffic pages, offline needs, or complex interactivity. Use Flow for admin panels, internal tools, or rapid prototyping with pure Java.

2. Keep endpoints stateless — @BrowserCallable services should not store per-user state in fields. Use method parameters and return values. Inject Spring services for data access.

3. Always add security annotations — endpoints are denied by default. Every public method needs @AnonymousAllowed, @PermitAll, or @RolesAllowed. Combine with loginRequired and rolesAllowed in ViewConfig for defense in depth.

4. Use signals over useState — useSignal from @vaadin/hilla-react-signals provides fine-grained reactivity with less boilerplate. Reserve useState for cases where you need React's rendering lifecycle (e.g., transitions).

5. Follow file naming conventions — use @index.tsx for directory indices, @layout.tsx for layouts, {param}.tsx for parameters. Prefix non-route files with _.

6. Handle endpoint errors — always wrap endpoint calls in try/catch. Distinguish EndpointValidationError (field-level issues) from EndpointError (server exceptions) and network errors.

7. Use ViewConfig for access control — set loginRequired and rolesAllowed on views, and matching security annotations on endpoints. This gives both client-side route protection and server-side enforcement.