Apache Felix Http Service

This is an implementation of the Http Service Specification as described in chapter 102 of the OSGi Compendium. The goal is to provide a standard and simplified way to register servlets and resources in a Servlet container, and to associate them with URIs. It also implement a non-standard extension for registering servlet filters as well as a whiteboard implementation. Complete set of features:

• Standard Http Service implementation.
• Extended Http Service implementation that allows for servlet filter registration.
• Run either with Jetty or inside your own application server using the servlet bridge.
• A whiteboard implementation for easy registration of servlets and filters.
• One complete bundle that includes everything to simplify deployment.

Installing

The Apache Felix Http project includes several bundles.

• org.apache.felix.http.jetty - Http Service implementation that is embedding Jetty server.
• org.apache.felix.http.whiteboard - Whiteboard implementation that uses any Http Service implementation.
• org.apache.felix.http.bridge - Http Service implementation that uses the host applicaiton server (bridged mode). Must be used with proxy.
• org.apache.felix.http.bundle - All in one bundle that includes all of the above.
• org.apache.felix.http.proxy - Proxy that is needed inside WAR when deployed inside an application server.

So, in most cases you could just use org.apache.felix.http.bundle and forget about all the other ones.

Using the HttpService

The main components provided by the Apache Felix Http Service bundle are:

• HttpService - Service used to dynamically register resources and servlets
• HttpContext - Additional (optional) component to handle authentication, resource and mime type mappings

Servlets created for the OSGi HTTP service don't need to have any reference to the OSGi specification (they only need to conform to the Servlet specification), like in the example:

public class HelloWorld extends HttpServlet
{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 
	{
           resp.getWriter().write("Hello World");		
	}	
}

To register a Servlet and map it to a URI, you need to retrieve the HttpService and call its registerServlet method:

public class Activator implements BundleActivator
{
	public void start(BundleContext context) throws Exception 
	{
		ServiceReference sRef = context.getServiceReference(HttpService.class.getName());
		if (sRef != null)
		{
			HttpService service = (HttpService) context.getService(sRef);
			service.registerServlet("/hello", new HelloWorld(), null, null);
		}
	}

In the same way, you can unregister a Servlet (for instance, in the stop method of the Bundle Activator) calling the HttpService.unregister method.

As you notice in the example above, the registerServlet method accepts four parameters:

• the Servlet alias
• the Servlet instance
• an additional configuration Map
• an HttpContext

The Servlet alias must begin with a slash and must not end with a slash. When a request is processed, the Http Service will try to exact match the requested URI with a registered Servlet. If not existent, it will remove the last '/' in the URI and everything that follows, and try to match the remaining part, and so on.

An additional configuration Map can be optionally specified; if present, all the parameters contained will be copied in the ServletContext object.

Finally, an HttpContext object can be optionally specified to handle authentication, mime type and resource mapping. The HttpContext interface is quite simple:

public interface HttpContext
{
   String getMimeType(java.lang.String name); //Returns the mime type of the specified resource
   URL getResource(java.lang.String name);   //Returns the URL to retrieve the specified resource
   boolean handleSecurity(HttpServletRequest request, HttpServletResponse response); //Manages security for the specified request
}

The use of a custom HttpContext is typical when you want to serve static contents with the HTTP Service. Let's see first the simplest example of resource registration (without HttpContext)

public class Activator implements BundleActivator
{
	public void start(BundleContext context) throws Exception 
	{
		ServiceReference sRef = context.getServiceReference(HttpService.class.getName());
		if (sRef != null)
		{
			HttpService service = (HttpService) context.getService(sRef);
			service.registerResources("/static", "/etc/www", null);
		}
	}

As a result of the service.registerResources("/static", "/etc/www", null) code, all the files available under /etc/www will be exposed under /static (f.i. http://localhost:8080/static/001.jpg will render the /etc/www/001.jpg). However, the example above can be simplistic in practice; the HttpContext object is the solution to customize the resource handling.

For instance, you can set the define more complex URI to file mappings overriding the HttpContext.getResource method, or the correct mime type implementing the method HttpContext.getMimeType like in the example:

    //....

	public String getMimeType(String file) 
	{  
	   if (file.endsWith(".jpg")
	   {  
	      return "image/jpeg";  
	   } 
	   else if (file.endsWith(".png")) 
	   {  
	      return "image/png";  
	   } 
	   else 
	   {  
	      return "text/html";  
	   }  
	}  
	
	//....

If you implement a customized HttpContext object, don't forget to specify it as third parameter of the registerResources method invocation:

public class Activator implements BundleActivator
{
	public void start(BundleContext context) throws Exception 
	{
		ServiceReference sRef = context.getServiceReference(HttpService.class.getName());
		if (sRef != null)
		{
			HttpService service = (HttpService) context.getService(sRef);
			HttpContext myHttpContext = new MyHttpContext());
			service.registerResources("/static", "/etc/www", myHttpContext);
		}
	}

Using the ExtHttpService

To be able to register filters, it is possible to get hold of org.apache.felix.http.api.ExtHttpService. This is exported by both jetty and the bridged implementation. Let's see the simplest example of a filter registration.

public class Activator implements BundleActivator
{
	public void start(BundleContext context) throws Exception 
	{
		ServiceReference sRef = context.getServiceReference(ExtHttpService.class.getName());
		if (sRef != null)
		{
			ExtHttpService service = (ExtHttpService) context.getService(sRef);
			service.registerFilter(new HelloWorldFilter(), "/hello/.*", null, 0, null);
		}
	}

Notice the pattern for filters is using regular expressions. So .
* is the same as a simple
* using standard servlet patterns.

Configuration Properties

The service can both be configured using OSGi environment properties and using Configuration Admin. The service PID for this service is "org.apache.felix.http". If you use both methods, Configuration Admin takes precedence. The following properties can be used (some legacy property names still exist but are not documented here on purpose):

• org.osgi.service.http.port - The port used for servlets and resources available via HTTP. The default is 80.
• org.osgi.service.http.port.secure - The port used for servlets and resources available via HTTPS. The default is 443.
• org.apache.felix.http.nio - Flag to enable the use of NIO instead of traditional IO. One consequence of using NIO with HTTPS is that the bundle needs at least a Java 5 runtime. The default is true.
• org.apache.felix.http.svcprop.port - The name of the property to use to set the HTTP port. The default is org.osgi.service.http.port.
• org.apache.felix.http.svcprop.port.secure - The name of the property to use to set the HTTPS port. The default is org.osgi.service.http.port.secure.
• org.apache.felix.http.enable - Flag to enable the use of HTTP. The default is true.
• org.apache.felix.https.enable - Flag to enable the user of HTTPS. The default is false.
• org.apache.felix.https.keystore - The name of the file containing the keystore.
• org.apache.felix.https.keystore.password - The password for the keystore.
• org.apache.felix.https.keystore.key.password - The password for the key in the keystore.
• org.apache.felix.https.truststore - The name of the file containing the truststore.
• org.apache.felix.https.truststore.password - The password for the truststore.
• org.apache.felix.https.clientcertificate - Flag to determine if the HTTPS protocol requires, wants or does not use client certificates. Legal values are needs, wants and none. The default is none.
• org.apache.felix.http.debug - Flag to enable debugging for this service implementation. The default is false.

Additionally, the all-in-one bundle uses the following environment properties:

• org.apache.felix.http.jettyEnabled - True to enable jetty as the http container. The default is false.
• org.apache.felix.http.whiteboardEnabled - True to enable the whiteboard implementation. The default is false.