Title: Servlet module
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# Configuration

In most cases there is no need for any additional configuration beside adding the required 
dependencies to your project, because all required listeners and filters are automatically 
registered in the container.

However there are certain situations in which you will have to manually register the 
listeners and filters in your `web.xml`:

* Your container doesn't support Servlet 3.0 or newer.
* You have set `metadata-complete=true` in your `web.xml`.
* You packaged the servlet module in the `lib` directory of an EAR archive.

In these cases you will have to add the following section manually to your `web.xml`:

    <listener>
        <display-name>EventBridgeContextListener</display-name>
        <listener-class>org.apache.deltaspike.servlet.impl.event.EventBridgeContextListener</listener-class>
    </listener>

    <listener>
        <display-name>EventBridgeSessionListener</display-name>
        <listener-class>org.apache.deltaspike.servlet.impl.event.EventBridgeSessionListener</listener-class>
    </listener>

    <listener>
        <display-name>ServletContextHolderListener</display-name>
        <listener-class>org.apache.deltaspike.servlet.impl.produce.ServletContextHolderListener</listener-class>
    </listener>

    <listener>
        <display-name>RequestResponseHolderListener</display-name>
        <listener-class>org.apache.deltaspike.servlet.impl.produce.RequestResponseHolderListener</listener-class>
    </listener>

    <filter>
        <display-name>RequestResponseHolderFilter</display-name>
        <filter-name>RequestResponseHolderFilter</filter-name>
        <filter-class>org.apache.deltaspike.servlet.impl.produce.RequestResponseHolderFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>RequestResponseHolderFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <filter>
        <display-name>EventBridgeFilter</display-name>
        <filter-name>EventBridgeFilter</filter-name>
        <filter-class>org.apache.deltaspike.servlet.impl.event.EventBridgeFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>EventBridgeFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>


# Injectable Servlet objects

The DeltaSpike Servlet module contains producers for many objects of a Servlet environment. 
All produces are using the special qualifier `@DeltaSpike` for compatibility with CDI 1.1, 
which supports the injection of some Servlet objects out of the box.

The following code shows the general injection pattern to use for all objects.

    @Inject @DeltaSpike
    private ServletObject servletObject;

## ServletContext

The `ServletContext` is made available in the application scope. It can be injected into any CDI bean 
like this:

    @Inject @DeltaSpike
    private ServletContext servletContext;

## ServletRequest / HttpServletRequest

The `ServletRequest` is made available in the request scope. The current request can be injected 
into a CDI bean like this:

    @Inject @DeltaSpike
    private ServletRequest request;

In case of HTTP requests you can also inject the `HttpServletRequest`:

    @Inject @DeltaSpike
    private HttpServletRequest request;

## ServletResponse / HttpServletResponse

The `ServletResponse` is made available in the request scope. The current response can be 
injected into a CDI bean like this:

    @Inject @DeltaSpike
    private ServletResponse response;

In case of HTTP requests you can also inject the `HttpServletResponse`:

    @Inject @DeltaSpike
    private HttpServletResponse response;

## HttpSession

The `HttpSession` is made available in the session scope. You can inject the current session 
of a user into a CDI bean like this:

    @Inject @DeltaSpike
    private HttpSession session;

Please note that injecting the session this way will force the creation of a session. 

## Principal

The `Principal` is made available in the request scope. The current principal can be 
injected into a CDI bean like this:

    @Inject @DeltaSpike
    private Principal principal;

The `Principal` is obtained by calling `getUserPrincipal()` on the `HttpServletRequest`.


# Servlet event propagation

The DeltaSpike Servlet module will propagate a number of Servlet object lifecycle events to 
the CDI event bus. This allows regular CDI beans to observe these events and react accordingly.

In most cases the event type is the object whose lifecycle is observed. To distinguish 
between construction and destruction of the corresponding object, DeltaSpike uses the 
qualifiers `@Initialized` and `@Destroyed`.

The following sections will show which concrete Servlet objects are supported and how their 
lifecycle can be observed.

## Servlet context lifecycle events

The Servlet module supports initialization and destruction events for the `ServletContext`. These events
can for example be used to detect application startup or shutdown. The following code shows
how these events can be observed:

    public void onCreate(@Observes @Initialized ServletContext context) {
        System.out.println("Initialized ServletContext: " + context.getServletContextName());
    }
    
    public void onDestroy(@Observes @Destroyed ServletContext context) {
        System.out.println("Destroyed ServletContext: " + context.getServletContextName());
    }

The events are emitted from a `ServletContextListener` called `EventBridgeContextListener`. You can
disable lifecycle events for the `ServletContext` by deactivating the following class:

    org.apache.deltaspike.servlet.impl.event.EventBridgeContextListener

If you manually registered the required filters and listeners, you can also simply remove the
entry for the `EventBridgeContextListener` from your `web.xml` to disable the events.

## Request and response lifecycle events

The Servlet module also supports initialization and destruction events for the `HttpServletRequest`
and `HttpServletResponse`. These events can for example be used for initialization work like invoking
`setCharacterEncoding` on the request.

The following example shows how to observe lifecycle events for the request:

    public void onCreate(@Observes @Initialized HttpServletRequest request) {
        System.out.println("Starting to process request for: " + request.getRequestURI());
    }
    
    public void onDestroy(@Observes @Destroyed HttpServletRequest request) {
        System.out.println("Finished processing request for: " + request.getRequestURI());
    }
 
Observing lifecycle events for the response works the same way:
 
    public void onCreate(@Observes @Initialized HttpServletResponse response) {
        System.out.println("HttpServletResponse created");
    }
    
    public void onDestroy(@Observes @Destroyed HttpServletResponse response) {
        System.out.println("HttpServletResponse destroyed");
    }

All events of this category are emitted from a servlet filter called `EventBridgeFilter`.
If you want to disable events for this category, just use DeltaSpike's deactivation mechanism
to deactivate the following class:

    org.apache.deltaspike.servlet.impl.event.EventBridgeFilter
 
If you manually registered the required filters and listeners you can also simply remove the
entry for the `EventBridgeFilter` from your `web.xml` to disable the events.

## Session lifecycle events

The last category of events supported by the DeltaSpike Servlet module are the lifecycle events
for the user's HTTP session. The following example shows how these events can be observed from
a regular CDI bean.

    public void onCreate(@Observes @Initialized HttpSession session) {
        System.out.println("Session created: " + session.getId());
    }
    
    public void onDestroy(@Observes @Destroyed HttpSession session) {
        System.out.println("Session destroyed: " + session.getId());
    }

The lifecycle events for the HTTP session are sent from a `HttpSessionListener` called
`EventBridgeSessionListener`. To disable this event category, deactivate the following
class:

    org.apache.deltaspike.servlet.impl.event.EventBridgeSessionListener
    
If you manually registered the required filters and listeners you can also simply remove the
entry for the `EventBridgeSessionListener` from your `web.xml` to disable the events.