Execution model

Mateu follows a fully stateless execution model. Every request is self-contained and reproducible.

Lifecycle per request

For each request:

Determine the ViewModel type from the route
Instantiate the ViewModel
Hydrate it with path parameters, query parameters, and form state sent by the browser
Execute the requested action (if any)
Serialize the result
Return the HTTP response
Discard the ViewModel

flowchart TD
    A[HTTP request] --> B[Determine ViewModel type]
    B --> C[Instantiate ViewModel]
    C --> D[Hydrate with request data\npath params · query params · state]
    D --> E[Execute action]
    E --> F[Serialize result]
    F --> G[HTTP response]
    G --> H[ViewModel discarded]

No server-side state

There is no persistent UI state between requests.

The browser holds the form state. On each interaction, it sends the current state to the server. The server hydrates a fresh ViewModel with that state, runs the action, and returns the result.

This means:

you cannot store UI state in instance fields across requests
there are no sessions to replicate
any two server instances produce identical results for the same request

What this enables

Horizontal scalability with no constraints — any instance can handle any request
No session management or replication infrastructure
Resilience to restarts and pod replacements
Consistent behavior across environments (local, staging, production)

Spring beans and services

ViewModels are instantiated by Mateu, not by Spring, but they can still inject services:

@UI("/products/new")
public class NewProductForm {

    @Autowired
    ProductRepository productRepository;

    @NotBlank
    String name;

    @Button
    public Message save() {
        productRepository.save(name);
        return new Message("Saved");
    }

}

Because the ViewModel is discarded after each response, injected beans are only used within that single request.

Mental model

Think of Mateu as:

UI = pure function (request state → response)

No hidden lifecycle. No long-lived server objects. No shared mutable state.