Web applications and web services - OSGi in Action - page 484

In this example, you define an HTTP-Resources manifest header that bundles can
use to specify resources they wish to register with the HTTP Service. You check
whether a bundle specifies any resources in the HTTP-Resources header B . The for-
mat of this header is a comma-delimited list of directories that may optionally be
aliased (you'll see this working in a second). If any resources are found, you create a
ProxyHttpContext (shown in the following listing) and register the resources with
the HttpService .

Listing 15.3 ProxyHttpContext for reading resources from a bundle

public class ProxyHttpContext implements HttpContext {

private final Bundle bundle;

public ProxyHttpContext(Bundle bundle) {
this.bundle = bundle;
}

B

Passes getResource()
to tracked bundle

public URL getResource(String name) {
return bundle.getResource(name);
}
...
}
If you used the default HttpContext , the HTTP Service would try to find the requested
resources in your ResourceTracker bundle, which clearly isn't correct. ProxyHttp-
Context attempts to find the resources in the bundle you're tracking. You create a
unique ProxyHttpContext for each tracked bundle. The key line of code in this class
passes the getResource() call through to the tracked bundle B .
To demonstrate how to use the resource tracker, the org.foo.http.resource bun-
dle in the chapter15/httpservice/ directory of the companion code contains the fol-
lowing header:

HTTP-Resources: /resource=html,/resource/images=images
If you deploy this bundle into an OSG i framework along with an HTTP Service and
your ResourceTracker , then its resources are registered; you can browse them at
http://localhost:8080/resource/index.html. This is just one trivial usage of the Http-
Context object. Other possible scenarios might include the following:

Managing authenticated access to web content

■

Mapping local file system resources into the HTTP Service

■

Now that you're familiar with registering static resources with the HTTP Service, let's
look at how it allows you to use servlets in an OSG i environment.

REGISTERING SERVLETS
Java servlets are the building block on which a vast number of web applications have
been built. Some of the key advantages of the servlet specification are the relative
simplicity of the API and the huge number of tools and frameworks available to help
you develop web applications with it. Similar to static content, the HTTP Service