Day: January 30, 2008

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Code Examples Should Work

I’m looking at Wicket this evening. There’s a wicket tutorial on theserverside.com. However, the first code example fails!

Initially I tried to get things working by downloading wicket. However, the article recommends maven (as does the quickstart), so I grit my teeth and went ahead.

Once again, I get 50 lines of gibberish, including an error. But everything seems to work. Clench teeth some more, and move on.

The first code example is the definition of the WicketApplication class, which Maven has helpfully created for us in outline. The first method to add is:

  private ApplicationContext getContext() {
    return WebApplicationContextUtils
      .getRequiredWebApplicationContext(getServletContext());
  }

As usual, I get compile errors. This is normal, just hit quick-fix in Eclipse to import the classes ApplicationContext. Except that there isn’t one.

Strike one.

I take a “lucky guess” and add a dependency on spring-web to my pom.xml. That makes both ApplicationContext and WebApplicationContextUtils appear on my classpath. Yay.

The next problematic method is this one:

  public static WicketApplication get() {
      return (WicketApplication) WebApplication.get();
  }

According to the tutorial:

The third overrides the Application#get() method to allow for covariant return types, in this case the WicketApplication class. This example uses the WicketApplication as a form of Service Locator.

Great! Except for the minor problem that it doesn’t compile:

  The return type is incompatible with Application.get()

Strike two.

For now, I’m going to comment it out and carry on playing until I get by bitten by that. But it’s not what I’d call a great start to a tutorial when your first code example is this buggy.

Update: I spoke to the author of the article, Nick Heudecker, and he pointed out:

  • I should have downloaded the example code, that works.
    • Well, great, but it would have been nice to have that mentioned.
  • Variant return types are supported by Java 5.
    • Which I certainly thought I was using. I don’t know what went wrong here. But I didn’t know that Java 5 could do this, so it’s good to know.