# Javax / Faces

## Overview

The `javax.faces` module is the root of the JavaServer Faces (JSF) package tree. JSF is a server-side component framework for building Java web applications using a component-based programming model. This module does not contain source files itself; instead, it serves as the organizational umbrella under which a set of sub-packages — most notably `javax.faces.webapp` — are grouped.

In a production JSF implementation (such as Mojarra or MyFaces), the framework would provide a rich set of APIs for managing UI components, handling request lifecycle phases, performing validation and conversion, rendering views in different markup languages (primarily HTML), and integrating with backing beans (managed POJOs) for business logic. The current codebase contains only stub definitions, indicating this appears to be a test fixture or scaffolding for the JSF API rather than a runnable implementation.

## Sub-module Guide

### `javax.faces.webapp`

This package bridges the servlet container and the JSF framework. Its primary purpose is to provide `FacesServlet`, which acts as the front-controller entry point for all HTTP requests that should be processed by the JSF lifecycle.

The `FacesServlet` class is defined in the codebase but currently contains no implementation body — it is a stub. In a real JSF runtime, this servlet would:

- Intercept HTTP requests matching a configured URL pattern (e.g. `*.jsf`, `/faces/*`).
- Bootstrap the JSF lifecycle phases: restore view, apply request values, process validations, update model values, invoke application, and render response.
- Create and manage the `FacesContext` — the request-scoped object that holds all state for a single JSF request.
- Wire into the `javax.servlet` APIs for reading the request and writing the response.

The servlet is registered in two web deployment descriptors (`web.xml` and `web-full.xml`), suggesting this project supports both standard and full Java EE profiles. Both descriptors reference `FacesServlet`, which means the servlet container is expected to dispatch matching requests to it at startup.

**How the sub-modules relate:** `javax.faces.webapp` is currently the only known child module under `javax.faces`. It depends on the broader JSF infrastructure (lifecycle, context, components) that would reside in sibling packages under this root. In a complete JSF distribution, packages like `javax.faces.component`, `javax.faces.lifecycle`, and `javax.faces.context` would work alongside `webapp` to deliver the full framework experience. The current codebase appears to be focused on the servlet integration point as the primary entry surface.

## Architecture

### Request Flow

In a fully implemented JSF application, the request flow through the `javax.faces` module follows a well-defined lifecycle:

```mermaid
flowchart TD
    A["Browser Request"] --> B["Servlet Container"]
    B --> C["FacesServlet.service()"]
    C --> D["JSF Lifecycle"]
    D --> E["Restore View"]
    D --> F["Apply Request Values"]
    D --> G["Process Validations"]
    D --> H["Update Model Values"]
    D --> I["Invoke Application"]
    D --> J["Render Response"]
    J --> K["HTML returned to Browser"]
```

The `FacesServlet` sits at the top of this flow, receiving raw HTTP requests and delegating them into the six-phase JSF lifecycle. Each phase transforms the request state further until a rendered response is sent back to the browser. Since `FacesServlet` is currently a stub, none of this processing occurs — the request flow is structural only.

### Design Decisions

The use of a front-controller servlet pattern is a deliberate JSF architectural choice. Rather than scattering request handling across many servlets, a single `FacesServlet` owns the entire request lifecycle, which enables:

- **Consistent lifecycle execution** — every JSF request passes through the same phases in the same order, guaranteeing predictable behavior.
- **Shared state management** — the `FacesContext` is created once per request and passed to all phases, avoiding state synchronization problems.
- **Separation of concerns** — view rendering is decoupled from request handling by the lifecycle's render phase, which delegates to component-specific renderers.

This appears to be a stub placeholder within a test fixture, as the `FacesServlet` class body is empty. The module is functional in structure (correct package, correct class name, wired into `web.xml`) but deferred in implementation.

## Dependencies and Integration

### Inbound Dependencies

| Consumer       | Role                                       |
|----------------|--------------------------------------------|
| `web.xml`      | Standard servlet registration and mapping  |
| `web-full.xml` | Full Java EE profile variant of config     |

These XML deployment descriptors declare and map `FacesServlet`. The servlet container reads them at application startup to register the servlet and route matching requests to it.

### Framework Dependencies (Expected)

In a complete JSF implementation, `javax.faces.webapp` would depend on:

- **`javax.servlet`** — for HTTP request/response handling.
- **`javax.faces.context`** — for creating and managing the `FacesContext`.
- **`javax.faces.lifecycle`** — for invoking the six lifecycle phases.
- **`javax.faces.component`** — for the component tree that represents the view.

The current stub has no declared dependencies beyond what the servlet container provides, since the class body is empty.

## Notes for Developers

1. **This is a stub.** `FacesServlet` is declared but contains no implementation. Production code relying on JSF request processing will need the implementation filled in.

2. **URL mapping governs behavior.** The requests that enter the JSF lifecycle are determined by the URL pattern configured in `web.xml` and `web-full.xml`. Common patterns include `*.jsf`, `*.faces`, or `/faces/*`.

3. **Only GET and POST are handled.** A real `FacesServlet` typically processes only GET and POST requests. Other HTTP methods are passed through unchanged and should be handled by servlet filters if needed.

4. **Single-instance lifecycle.** Like all servlets, `FacesServlet` is instantiated once per web application. Any state stored as instance variables must be thread-safe.

5. **Multiple deployment descriptors.** The presence of both `web.xml` and `web-full.xml` means this project targets both standard and full Java EE profiles. Ensure both files define consistent servlet mappings to avoid divergent behavior across profiles.

6. **No source files indexed.** The parent `javax.faces` module contains no indexed source files or classes directly — all symbols are defined within its sub-packages, primarily `javax.faces.webapp`.