# Javax

## Overview

The `javax` package at the root level serves as a **namespace root for the JavaServer Faces (JSF) specification** within this codebase. It does not contain any indexed source files or classes directly — instead, it organizes a hierarchy of subpackages that together implement (or, in this codebase, document) a component-based, event-driven web framework for building Java web applications.

JSF follows the **Page Controller pattern**, centering around a request processing lifecycle that maps HTTP requests to UI component trees, processes form submissions, and renders responses. The `javax.faces` subpackage is the core entry point into this framework.

This documentation area describes the **standard JSF specification contract** (based on the Oracle reference implementation, Mojarra, or the Apache MyFaces implementation). The local codebase contains only stub or placeholder content, suggesting it is intended as a reference rather than a runtime implementation.

## Sub-module Guide

### `javax.faces.webapp` — Servlet Entry Point

The `webapp` sub-package is the **bridge between the Java Servlet API and the JSF framework**. It exposes `FacesServlet`, the central dispatcher that intercepts HTTP requests based on URL patterns configured in `web.xml` (e.g., `*.jsf`, `/faces/*`).

**How it relates to the broader system:**

`FacesServlet` is the gateway — everything in JSF flows through it. It does not implement the lifecycle itself but delegates to classes in `javax.faces.lifecycle` (for phase execution) and `javax.faces.context` (for per-request state). This makes the `webapp` package **thin and delegating by design** — it handles HTTP protocol concerns while the heavy lifting (component tree management, validation, model binding, rendering) lives in sibling sub-packages.

## Key Patterns and Architecture

### The Request Processing Lifecycle

The dominant architectural pattern in `javax.faces` is the **template method pattern** realized through the JSF request processing lifecycle. Each incoming request progresses through six ordered phases:

1. **Restore View** — Loads the existing component tree or creates a new one.
2. **Apply Request Values** — Populates UI component values from HTTP request parameters.
3. **Process Validations** — Runs registered validators against submitted values.
4. **Update Model Values** — Copies validated data into backing beans (managed beans or CDI beans).
5. **Invoke Application** — Executes action listeners, navigation rules, and business logic.
6. **Render Response** — Builds the HTML (or other format) response from the component tree.

This lifecycle ensures a consistent, structured processing model. `FacesServlet` invokes the lifecycle; individual phases are handled by collaborators in other sub-packages.

### Servlet-to-Faces Context Bridge

`FacesServlet` implements a **bridge pattern** between two incompatible APIs: the raw `HttpServletRequest`/`HttpServletResponse` from the Servlet API, and the rich `FacesContext`/`ExternalContext` abstractions used by the rest of JSF. This separation allows the framework to remain agnostic of the underlying HTTP transport while providing a unified programming model.

```mermaid
flowchart TD
    REQ["HTTP Request"] --> FACES["FacesServlet
javax.faces.webapp"]
    FACES --> CTX["FacesContext
javax.faces.context"]
    FACES --> LIFECYCLE["Lifecycle
javax.faces.lifecycle"]
    CTX --> COMP["UIComponent
javax.faces.component"]
    LIFECYCLE --> RVIEW["Restore View"]
    LIFECYCLE --> ARVAL["Apply Request Values"]
    LIFECYCLE --> PVALID["Process Validations"]
    LIFECYCLE --> UMODEL["Update Model Values"]
    LIFECYCLE --> INVOKE["Invoke Application"]
    LIFECYCLE --> RENDER["Render Response"]
    RENDER --> RESP["HTTP Response"]
    COMP --> MODEL["Backing Beans
Managed/CDI"]
```

## Dependencies and Integration

### Outbound Dependencies

The `javax.faces` hierarchy depends on a set of sibling sub-packages that form the core JSF runtime:

| Dependency | Purpose |
|---|---|
| `javax.faces.context` | Provides `FacesContext` and `ExternalContext` — the per-request state carrier |
| `javax.faces.lifecycle` | Provides `Lifecycle` and `LifecycleFactory` — the phase execution engine |
| `javax.faces.component` | Provides the `UIComponent` tree — the component model for views |
| `javax.servlet.*` | Provides the `Servlet` interface and HTTP request/response types |

### Inbound Dependencies

| Artifact | Relationship |
|---|---|
| `web.xml` / `web-full.xml` | Declares and maps `FacesServlet` to URL patterns |

The `javax.faces` package has no indexed source files of its own, meaning all functionality is distributed across its sub-packages. It functions as a **namespace root** rather than a package with its own implementations.

## Notes for Developers

### Stub Implementations

The local codebase contains stub classes (e.g., `FacesServlet` with an empty class body). The real JSF implementation is expected to come from a transitive dependency such as Mojarra (the Oracle reference implementation) or MyFaces (the Apache implementation). Documentation in this area describes the **standard JSF specification contract**, not local code.

### Configuration Conventions

- A single `FacesServlet` is typical per JSF application.
- URL pattern selection matters — patterns like `*.jsf` or `/faces/*` determine which requests trigger the lifecycle. Static resources (CSS, JS, images) should not match these patterns, or JSF 2.0+ resource handling must be configured to exclude them.

### Extension Points

- **Custom `Lifecycle`**: Developers can register custom lifecycle implementations to inject behavior (logging, security checks, performance monitoring) around the standard phases.
- **`@FacesServletMapping`**: JSF 2.3+ supports annotation-based servlet mapping as an alternative to `web.xml` configuration.
- **Phase listeners**: Implement `PhaseListener` to intercept specific lifecycle phases.

### AJAX Handling

AJAX requests (via `<f:ajax>` or third-party libraries) are routed through the same `FacesServlet` but trigger partial processing — only the relevant components and view fragments are re-rendered, rather than the entire page.