Java Servlets

Using Google's App Engine for Java, the server side coding is done using Java Servlets.

Servlets are just Java classes that get run on the server when a web browser requests a URL. A servlet can handle just one specific URL, or a range of URLs using wildcards. You specify which URLs a servlet handles using a URL mapping. The Java class when run must output something that will get sent back to the user's web browser...typically HTML, but in the case of GWT the servlet may return data that gets parsed on the client side.

Open up your web application project in Eclipse, and open war/WEB-INF/web.xml. Eclipse parses out the XML and shows you a structured editor for it. Click on the plus sign beside web-app. The servlet section defines what servlets are available, and the servlet-mapping section defines the mappings between those servlets and URLs.

The sample application has just a single servlet, and a single mapping for that servlet. We need a servlet to handle the RPX results, and we need that to map to /rpxresults. We could just replace the sample servlet, but we need to add new ones eventually, so let's go ahead and add a new one.

You could fool around with Eclipse's XML editor to do this, but I prefer to work in text. Right click on the web.xml file in the project list, and choose Open With->Text Editor. Copy the <servlet> and <servlet-mapping> sections and paste them at the bottom of the file, just after </servlet-mapping>.

Change the servlet-name to some name that you'll use to refer to this servlet in web.xml. Change the servlet-class to the name of the servlet class (we haven't written that yet, so just make this what you plan to name that class). Follow the same package naming that the sample servlet uses, typicall "project.server.classname".

In the servlet-mapping section, change the servlet-name to match what you used above, and change the url-pattern to /rpxresults. That should make the server aware of the servlet and have that servlet invoked when anyone tries to go to /rpxresults.

Now we just need to write the actual servlet class.