To introduce NetKernel from a code perspective we will demonstrate a Hello World! example program written in Java. The program is activated when a browser requests the web resource located at http://localhost:8080/tutorial/helloworld. When you click on this link the example code returns "Hello World".

Code in NetKernel resides in modules. Modules may exist as a Java Archive (JAR) file or file system directory. Standard modules supplied with NetKernel are located in the modules/ directory located directly beneath the directory in which you installed NetKernel - in the documentation this path is given the shorthand: [install]. The tutorial module is located at [install]/modules/tutorial/. The Java class for this example is located within the tutorial directory in the file org/ten60/netkernel/tutorial/HelloWorld.java. You can edit the Java source code and when it is saved NetKernel will detect the change and automatically recompile it. Just reissue your browser request to test the change.

When a browser sends a request to NetKernel a corresponding request for a resource at a logical URI address is issued within NetKernel - for the moment don't worry about the details of how the HTTP request is routed to an internal NetKernel URI addresses. What is important is that an HTTP request arriving at NetKernel's HTTP transport causes an internal URI request to be issued inside NetKernel's logical Web-like software address space.

When an internal request is created and issued, it is routed to a software endpoint called an Accessor and the accessor's processRequest() method is called. The following processRequest() method returns our message wrapped in an immutable StringAspect object. (An essential tenet of resource oriented computing is that all resource requests result in an immutable resource representation being returned.)

public void processRequest(INKFConvenienceHelper context) throws Exception
{
  // Create an immutable StringAspect wrapper for our text message
  IURAspect aspect = new StringAspect("Hello World");

  // Create a response object containing the StringAspect
  INKFResponse response = context.createResponseFrom(aspect);

  // Set metadata indicating the MIME type of the response
  response.setMimeType("text/plain");

  // Set metadata indicating the response can be cached
  response.setCacheable();
}

When the processRequest() method is called it receives a context object which provides access to information about the request (such as its logical URI, its parameters, etc). When the method exits the response object created earlier is automatically returned to the calling client.

If you are familiar with Java J2EE development this may appear similar to a Servlet. In some ways NetKernel's resource oriented computing model is an extension of the World Wide Web so a similarity between a servlet and a NetKernel accessor should not be surprising. The Web is resource oriented just like NetKernel. Unlike the Web, NetKernel applies ROC to all internal software - down to the smallest service and the microkernel itself. NetKernel brings the Web Inside ... but there is more to this story ...