Fabrizio Giudici is a Senior Java Architect with a long Java experience in the industrial field. He runs Tidalwave, his own consultancy company, and has contributed to Java success stories in a number of fields, including Formula One. Fabrizio often appears as a speaker at international Java conferences such as JavaOne and Devoxx and is member of JUG Milano and the NetBeans Dream Team. Fabrizio is a DZone MVB and is not an employee of DZone and has posted 67 posts at DZone. You can read more from them at their website. View Full User Profile

Using the NetBeans Platform on the Server with Wicket on the Client

01.07.2009
| 35185 views |
  • submit to reddit
This is the Servlet Decorator:
package it.tidalwave.netbeans.servlet;

import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.openide.util.Lookup;

public class NetBeansPlatformDecoratorServlet implements Servlet
{
private ServletConfig config;
private Servlet delegate;

public void init (final ServletConfig config)
throws ServletException
{
try
{
NetBeansPlatformUtils.boot(config.getServletContext());
}
catch (Exception e)
{
throw new ServletException(e);
}

final ClassLoader classLoaderSave = NetBeansPlatformUtils.installPlatformClassLoader();

try
{
this.config = config;
final String className = config.getInitParameter("netbeans.servlet.delegate");
final Class delegateClass = Thread.currentThread().getContextClassLoader().loadClass(className);
delegate = (Servlet)Lookup.getDefault().lookup(delegateClass);

if (delegate == null)
{
throw new RuntimeException("Can't lookup " + className);
}

delegate.init(config);
}
catch (Exception e)
{
throw new ServletException(e);
}
finally
{
Thread.currentThread().setContextClassLoader(classLoaderSave);
}
}

public ServletConfig getServletConfig()
{
return delegate.getServletConfig();
}

public void service (final ServletRequest req, final ServletResponse res)
throws ServletException, IOException
{
final ClassLoader classLoaderSave = NetBeansPlatformUtils.installPlatformClassLoader();

try
{
delegate.service(req, res);
}
catch (Exception e)
{
throw new ServletException(e);
}
finally
{
Thread.currentThread().setContextClassLoader(classLoaderSave);
}
}

public String getServletInfo()
{
return delegate.getServletInfo();
}

public void destroy()
{
final ClassLoader classLoaderSave = NetBeansPlatformUtils.installPlatformClassLoader();

try
{
delegate.destroy();
}
finally
{
Thread.currentThread().setContextClassLoader(classLoaderSave);
}
}
}

These are the main concepts:

  1. As usual for decorators, the behaviour is forwarded to a delegate.
  2. The decoration consists in setting the context class loader (Thread.currentThread().getClassLoader()) from the NetBeans Platform and restoring it at the end of the method call (taking care of using a finally block for safety). The details are implemented in the NetBeansPlatformUtils class, discussed below.
  3. The delegate instance is retrieved by asking it to the Lookup class, as usual for NetBeans Platform applications (this is why you had to declare all the relevant Servlets and Filters in META-INF/services as previously described). While the common idiom is to pass the class literal as argument (e.g. MyService s = Lookup.getDefault().lookup(MyService.class)), here we can't do that for two reasons: first, because we want the code to be universal, so the class name must be passed in a parameter ("netbeans.servlet.delegate"); and second, because we couldn't get the literal in any way, since it would be never available in the static compilation classpath (there are no good ways to have a .war statically include the Platform stuff; if you tried to extract the .jar files from the .nbm modules - which per se is a cumbersome approach - you would face possible ClassCastExceptions since you would have the same class available in both Tomcat and the Platform class loaders - remember that the same bytecode in two different classloaders is treated as two different classes).
  4. Last but not least, at the first invocation of a Servlet or Filter delegate you must initialize the Platform: that's the task of NetBeansPlatformUtils.boot(). 

Published at DZone with permission of Fabrizio Giudici, author and DZone MVB.

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)

Comments

Harris Goldstone replied on Fri, 2009/01/09 - 3:25pm

In a Wicket application, what is some of the typical functionality that I could let the NetBeans Platform handle?

Fabrizio Giudici replied on Sun, 2009/01/11 - 7:12am

Hi Harris.

At the moment, the great advantage is for what concerns the tier of services and models, that is the business tier. It is something that can be best clarified by examples, and I'll post some in future here on DZone (also with other two "series" of posts about NetBeans Platform Idioms etc...); for the moment, take this small one: I have a Metadata infrastructure that allow to extract metadata from media (e.g. photos), eventually store them in a database, where they can be searched for. Every kind of metadata (EXIF, IPTC, whatever) is implemented by separate modules, as well as persistence in the database is enabled by just adding specific modules, without requiring any configuration. This means that I can easily satisfy different needs (blueMarine itself, blueOcean base, blueOcean as used by my customer, and hopefully other future customers) by just assembling different set of modules in specific custom platforms. This has been achieved mostly by means of the Lookup API (and in future I could use more the layer.xml facility). Most of this stuff could be used also by taking simple .jars as libraries out of the NetBeans Platform; but as the number of configurations increases, it is really important to have the capability of checking compatibilities and dependencies among modules. You could be always safe with a good testing, but in any case I appreciate when a static tool finds / prevents problems as early as possible. Furthermore, having the very same process for two different projects is a big time saver for me.

There are two different uses of the Platform that I'll evaluate soon. First is the "Event Bus" (based on "Central Lookup" by Wade Chandler) that I've talked about a few months ago; in blueMarine it introduces another great deal of decoupling that in the customer's project based on blueOcean I don't have yet. While the Event Bus as is works fine with a single user (it is a singleton), it must be adapted in the case of concurrency (it should be enough to write a variant based on ThreadLocal). Second is about the use of Nodes for a number of things, including dynamic generation of menus based on the functions that you have dynamically included in the current configuration. This is more sensible because of the cited potential problem with the AWT Thread, which would be a serious bottleneck on the server side.

Aldo Brucale replied on Mon, 2009/01/19 - 8:49am

How can I access org.netbeans.Main from my module? It belongs to the Bootstrap module, but when I add this dependency and try to compile, the build system says that the module containing NetBeansPlatformUtils "is not a friend of <nb-platform-dir>/nbbuild/netbeans/platform9/lib/boot.jar".

Fabrizio Giudici replied on Mon, 2009/01/19 - 9:08am

Actually I've never used the o.n.Main from a Platform module - since it's boot code, I've used it from plain JSE code, and of course I've just included the relevant .jar in the path. For what reason do you need to access o.n.Main from a _Platform_ module? Before searching for you a solution to your question, maybe we can find another, better way to do the thing you're trying.

Aldo Brucale replied on Mon, 2009/01/19 - 11:22am in response to: Fabrizio Giudici

Thank you Fabrizio, of course a module cannot boot the application that is supposed to load it!

I placed the servlet in a regular web project, now it works perfectly. Very interesting, thank you.

Matthew Dempesy replied on Sat, 2011/01/08 - 9:30pm

The module which I was planning to work was purely based on server side application only. I would prefer to use netbeans on my Cloud Hosting server platforms. I have not tried it fully. I would hope that things go cool, without creating much of problems to my head. This writeup which is concerned with the server side process would certainly help me in achieving my goals. If any help I would need I would be here to clear that.

Matt Coleman replied on Thu, 2013/02/21 - 1:09am in response to: Fabrizio Giudici

thanks for explaining this issue Fabrizio..I now understand why

buffalo freelance web designer 

Cata Nic replied on Tue, 2013/09/03 - 3:17am

 Is it possible to use a CDN solution for that. I mean... it will be useful to offer a part of the data via a CDN.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.