How do I make a global helper servlet for all applications?

Question

I am running about five different web applications in tomcat 5.0.24. They all need to do some spelling correction from time to time. I have a spelling correction API and a bunch of dictionaries, etc. so I can do it just fine. The problem is, I don't want each application to create all the dictionaries because then I end up with five spell checking programs and five dictionaries being accessed (basically I am exactly repeating myself five times and I start running out of memory). I would like to have a servlet that just sits waiting all the time and which any other servlet or JSP in any of my web applications can quickly dash of a spell check request to at any time.
How do I do this?
I think I need to write a servlet since I want to run it in tomcat and access it from my webapps, but it might not need to be a servlet since it is never actually contacted from a browser and will not ever write anything back to the client. I just need my other servlets and JSPs to access the spell checking functionality from time to time.

Answer 1

I'd say tomcat/common/lib is a good guess for where you'd put the class's jar file, but I don't use Tomcat so I can't say for sure. As for how to only have one dictionary, you need a singleton class, i.e. one that only permits one instance of the class to be created. Like this, if you haven't heard of it:public class SpellChecker {
  // create a single SpellChecker here:
  private SpellChecker theInstance = new SpellChecker();
  // don't let anybody else create another one:
  private SpellChecker() {}
  // provide a method for returning the single instance:
  public static SpellChecker getInstance() {
    return theInstance;
  // remaining methods go here
  // watch out for synchronization issues
}To get hold of the spell-checker, just doSpellChecker.getInstance()PC²