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Monday, December 5, 2011

Reading Spring Controller and RequestMapping Definitions

My current, major task at work is to bring two existing web applications into one utilizing a single-signon mechanism and overhaul the UI based on my recommendations previously made.  Part of the background architecture work involved in allowing the creation of a menu structure that would ultimately be utilized to create a similar structure in the UI.

I wanted to use JAXB to unmarshall my menu XML into Java objects but I suspect the complex nature of the XML schema and some limitations of the JAXB framework combined with my lack of a complete understanding of JAXB hindered this process to such a degree that I had to stop due to the time I was spending on it.  So, instead of getting the created objects "for free" I had to resort to writing my own SAX Parser event handler to build up the menu structure in Java land.  I had tried a DOM-based approach first, but the recursive nature of the elements made me cringe a bit while writing the code and if you ever have the thought of "there's got to be an easier way to do this" while writing code, your best bet is to just flat out stop what you are doing and take some time to thoroughly think things through before spending any more time on the task.

The event handler also built up the menu item URI paths using attributes on the hierarchical menu structure in the menu XML.  This gave the menu item actions (arbitrary) name-spacing.  I say arbitrary because when using Spring MVC with only one DispatcherServlet, the URI paths are essentially meaningless.

One other thing I wanted to ensure was that we would never have a dangling menu item - that is a menu item defined (and in the UI) but not actually tied back to a Spring Controller method.  So, I created a unit test that loads my menu XML, pulls a list of all the RequestMapping annotated methods, and confirms that every menu item ties back to a server-side method.

Here's the code:

  Map<String, Object> controllers =
    this.ctx.getBeansWithAnnotation(Controller.class);
  for(Map.Entry<String, Object> entry : controllers.entrySet()) {

    Class controllerClass = entry.getValue().getClass();
    for(Method method : controllerClass.getDeclaredMethods()) {

      RequestMapping rm =
        method.getAnnotation(RequestMapping.class);
      if(rm == null) {
        continue;
      }
      else {

        String[] vals = rm.value();
        if (vals.length == 1) {
          this.mappingSet.add(vals[0]);
        }
        else {
          String msg =
            "this test assumes only one request mapping per method.  " +
            "check class: " + controllerClass + " and method: " + method;
          Assert.fail(msg);
        }
      }
    }
  }

Two notes:

  1. The reference "this.ctx" refers to a Spring ApplicationContext, in my case here an instance of the XmlWebApplicationContext class that loads my Spring configuration.
  2. The reference "this.mappingSet" is simply a class-local field (HashSet<String>) in which I simply store the RequestMapping values.
Finally, after this is complete I confirm that every menu item action URI is contained in the set of extracted RequestMapping values.

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