# Javax / Faces / Webapp

## Overview

The `javax.faces.webapp` package is the web-layer entry point for the JavaServer Faces (JSF) framework. It exposes the `FacesServlet` — a `javax.servlet.Servlet` implementation that acts as the central dispatcher for all HTTP requests in a JSF application. When deployed, the FacesServlet intercepts incoming requests, routes them through the JSF lifecycle, and manages the rendering of component-based UIs back to the client.

## Key Classes and Interfaces

### FacesServlet

**Source:** [`FacesServlet.java`](full-fixture-codebase/src/java/javax/faces/webapp/FacesServlet.java)

The `FacesServlet` is the primary servlet in a JSF application. It is the single entry point that allFaces-related requests flow through, serving as the front controller for the framework.

In this codebase the source file is currently a stub:

```java
package javax.faces.webapp;
public class FacesServlet {}
```

In a fully-implemented JSF deployment, this class would extend `javax.servlet.http.HttpServlet` and implement the full request-processing pipeline:

- **`init()`** — Initializes the Faces servlet context, often bootstrapping the `FacesContext` factory and loading application configuration.
- **`service()` / `doGet()` / `doPost()`** — Intercepts incoming HTTP requests, determines whether the request matches a JSF mapping (typically `*.jsf`, `*.faces`, or `/faces/*`), and delegates to the JSF lifecycle.
- **`initFacesContext()`** — Creates and scopes a new `FacesContext` instance per request, which holds all request-scoped state (parameters, attributes, view references).
- **`releaseFacesContext()`** — Cleans up the `FacesContext` after the request completes to avoid memory leaks.

#### Lifecycle delegation

In a complete implementation, the FacesServlet coordinates the JSF lifecycle in six phases:

1. **Restore View** — Reconstructs the component tree from the saved view state.
2. **Apply Request Values** — Populates component local values from the request.
3. **Process Validations** — Runs validators on each component.
4. **Update Model Values** — Writes validated values into backing beans / model objects.
5. **Invoke Application** — Fires application-level events (e.g., button action handlers).
6. **Render Response** — Builds the HTML (or other format) response from the component tree.

## How It Works

### Request Flow

When a client makes an HTTP request to a URL mapped to the FacesServlet (as defined in `web.xml` or `web-full.xml`), the servlet:

1. Checks if the request is a postback (a form submission that originated from a JSF page) or an initial page load.
2. If a postback, validates the view state to prevent tampering.
3. Creates a `FacesContext` for the current request.
4. Executes the six-phase JSF lifecycle.
5. Renders the response and cleans up.

The FacesServlet is typically configured with a URL pattern like `*.jsf` or `/faces/*`, which means all requests ending in those patterns are routed through JSF processing. Non-JSF requests pass through unmodified.

### Cross-Module Relationships

The FacesServlet is registered in the application's web deployment descriptors:

```mermaid
flowchart TD
    WebXML["web.xml"] -->|registers servlet mapping| FacesServlet["FacesServlet"]
    WebFullXML["web-full.xml"] -->|registers servlet mapping| FacesServlet
```

Both `web.xml` and `web-full.xml` reference `FacesServlet` in their servlet configurations, meaning the servlet is set up through the standard Java EE web deployment mechanism.

## Data Model

This package does not define any entity, DTO, or data model classes. The FacesServlet operates on JSF's internal data structures — primarily the `FacesContext` instance (per-request state) and the `UIViewRoot` component tree — which are defined in the broader `javax.faces` package hierarchy.

## Dependencies and Integration

- **`web.xml`** — Standard Servlet API deployment descriptor that registers and maps the FacesServlet.
- **`web-full.xml`** — Full Java EE profile deployment descriptor with the same FacesServlet registration.
- **`javax.servlet.*`** — The FacesServlet is a servlet and depends on the Servlet API for HTTP request/response handling.
- **`javax.faces.*`** — The FacesServlet delegates core processing to the JSF framework classes (lifecycle, context management, component tree, render kit) in the `javax.faces` package and its subpackages.

## Notes for Developers

- This source file is a minimal stub. A production FacesServlet would contain the full lifecycle delegation logic. If you are implementing this class, refer to the [Java EE / Jakarta EE JSF specification](https://jakarta.ee/specifications/faces/) for the complete lifecycle API.
- The servlet is registered via standard web deployment descriptors (`web.xml`, `web-full.xml`), so it follows the conventional Java EE servlet configuration patterns — no special bootstrapping is required beyond what the application server handles.
- URL mapping is the primary configuration point for controlling which requests JSF processes. The mapping is defined in the deployment descriptor, not in code.
- In modern Jakarta EE applications (Jakarta Faces / JSF 3.x+), the package would be `jakarta.faces.webapp` instead of `javax.faces.webapp`.