StateSupplier

By default, Mateu serialises the ViewModel itself as the component state sent to the browser. StateSupplier lets you return a different object instead — useful when the state the client needs is a projection, a DTO, or a computed view of the ViewModel’s internal data.

public interface StateSupplier {
    Object state(HttpRequest httpRequest);
}

The returned object is serialised to JSON and sent to the browser as the component’s initial state. Field values in the returned object become available in client-side rule expressions as state.<fieldName>.

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When to use it

Use StateSupplier when:

• The ViewModel contains fields that should not be exposed to the client (e.g., internal service references, sensitive data).
• The client state is a computed projection rather than the raw ViewModel fields.
• You need to control exactly what is serialised without using @Hidden on every private field.

If you only want to hide a few fields, @Hidden or VisibilitySupplier is simpler. StateSupplier gives you full control at the cost of having to manage the projection manually.

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Example

@UI("/orders/{id}")
public class OrderForm implements StateSupplier {

    private final OrderService orderService;  // injected — should not reach the client
    public String orderId;
    public String status;
    public double total;

    public record OrderState(String orderId, String status, double total) {}

    @Override
    public Object state(HttpRequest httpRequest) {
        return new OrderState(orderId, status, total);
    }
}

Only orderId, status, and total are sent to the browser; orderService is never serialised.