[equinox-dev] JSP support in the servlet bridge incubator project

[Richard Backhouse <backhous@xxxxxxxxxx>]

I have spent a little time investigating
supporting JSPs within the server side OSGi incubator project. Having taken
a look at what Harald Niesche had achieved with his JasperBundle I felt
that instead of having to prefix all my JSP requests with "/jasper-jsp"
it would be preferable to support JSP's just as requests for static resources
are handled.

Here is what I have put together :

1.) Created a org.apache.jasper bundle
containing the required Jasper jars to run the JSP Container (commons-el.jar,
jasper-compiler.jar, jasper-compiler-jdt.jar and jasper-runtime.jar). This
bundle is also a fragment bundle whose bundle host is org.eclipse.equinox.servlet.bridge.http
bundle. This allows references to the Jasper classes to be made without
having to add explicit imports to the org.eclipse.equinox.servlet.bridge.http
manifest.

2.) In the org.eclipse.equinox.servlet.bridge.http
bundle I created a JspEnabledProxyServlet class that extends the ProxyServlet
class. Within this new class a single JSPServletRegistration object is
created that wrappers the Jasper org.apache.jasper.servlet.JspServlet.
Also a specialized JspServletHtpContext class has been created to handle
setting the correct resouce http context for the bundle that contains the
JSP resource.

3.) In the org.eclipse.equinox.servlet.bridge.http
bundle I created a JspEnabledResourceRegistration class that extends the
existing ResourceRegistration class and overides the handleRequest method.
When created it is passed a reference to the JSPServletRegistration object
.When the  handleRequest method is called if the supplied alias has
an extension identified as a JSP extension the JSPServletRegistration object
is used to handle the request instead of the standard ResourceRegistration.


4) All of the above is enabled by making
some slight modifications to some of the org.eclipse.equinox.servlet.bridge.http
classes, specifically the Activator class and the ProxyServlet class. The
ProxyServlet changes were simply changing some of the class attributes
and methods to protected access. The change to the Activator class was
to invoke the new JspEnabledProxyServlet instead of the standard ProxyServlet.
The manifest for the org.eclipse.equinox.servlet.bridge.extensionbundle
was also modified to filter the javax.servlet.jsp classes down from the
running webcontainer.
 
So this works nicely for any JSP resources
configure via the standard resources extension point but what if the JSP's
reference Custom Tag Libraries ? The solution I have come up with allows
Custom Tag Libraries to be created as standard OSGi bundles. They register
their provided TLD's via a TldProvider service I added to the org.eclipse.equinox.http.registry
bundle. The JspEnabledProxyServlet class tracks the registered services
and adds their  TLD uri's to the Jasper JSP Servlet. via an extended
URLClassloader  I could have achieved the registration of the TLDProviders
by using a new extension point added to the org.eclipse.equinox.http.registry
bundle but getting access to the registry details seemed as though it would
be quite hard to achieve in simple manor. 

Thoughts ?

Richard Backhouse