Implementing Facade in Java

Facade: A simplified interface that coordinates a subsystem so most callers can use it without understanding every internal collaborator.

In Java, a facade often sits at an application boundary such as:

• checkout orchestration
• document conversion
• report generation
• media processing

Start With The Use Case

The facade should reflect the task the caller wants done:

1public interface CheckoutFacade {
2    CheckoutResult placeOrder(CheckoutCommand command);
3}

That is stronger than exposing five subsystem services and asking each caller to orchestrate them correctly.

A Small Java Example

 1public final class DefaultCheckoutFacade implements CheckoutFacade {
 2    private final InventoryService inventory;
 3    private final PricingService pricing;
 4    private final PaymentService payments;
 5    private final OrderService orders;
 6
 7    public DefaultCheckoutFacade(
 8            InventoryService inventory,
 9            PricingService pricing,
10            PaymentService payments,
11            OrderService orders) {
12        this.inventory = inventory;
13        this.pricing = pricing;
14        this.payments = payments;
15        this.orders = orders;
16    }
17
18    @Override
19    public CheckoutResult placeOrder(CheckoutCommand command) {
20        inventory.reserve(command.items());
21        Money total = pricing.totalFor(command.items(), command.customerId());
22        PaymentReceipt receipt = payments.charge(command.paymentToken(), total);
23        return orders.create(command, total, receipt.reference());
24    }
25}

This facade owns sequencing and subsystem collaboration, but it does not replace the underlying services. It simply gives most callers one coherent entry point.

What A Facade Should Not Become

Avoid turning the facade into:

• a giant god service
• the only place where all business logic is allowed
• a dependency sink with dozens of collaborators

If every operation in the subsystem ends up on one facade, the boundary is probably too broad.

Design Review Questions

• What common task is the facade making simpler?
• Which subsystem details are intentionally hidden?
• Which advanced operations still deserve direct access elsewhere?

Facade is strong when it simplifies common use, not when it monopolizes all access for style reasons.