I’m a big fan of Apache Wicket, but there’s an urgent need for a better-organized component-ecosystem around Wicket. To write a real web application you need a framework (that’s Wicket) and visual components (that’s JQuery, YUI, Recaptcha etc) and you need the two to work together smoothly. A newcomer to Wicket should be impressed by the clean, component-oriented approach to producing the GUI for his application, but a production web application needs more than just HTML. So, inevitably, the next step is to try to find the stuff which will make your web-application look like all those other web 2.0 sites out there. However, very few of the Wicket components referenced from the Wicket home pages are “best-of-breed” and a[…]

Yesterday we had a bug caused by the following situation: a class X had a variable “user”. Class X had an inner, anonymous class extending class Y. Inside the inner class a reference was made to the “user” variable from the enclosing class X. Somebody then added a protected variable “user” to class Y. The java compiler silently updated the reference to “user” within the inner class from X.user to Y.user. This is pretty nasty and I hoped that some of the code-checking tools would warn about about it, so I checked the code with PMD, Findbugs and Checkstyle. Unfortunately, none of them flagged the issue.

If you work with anonymous classes a lot (as Wicket applications do), you sometimes get confronted with compiler/tool messages referring to anonymous (inner) classes with names like MyPage$1$1$2 (for instance in FindBugs reports). Its pretty tedious to figure out which class is meant. Maybe there’s a better way, but what I do is go to the target directory and call “javap MyPage$1$1$2.class”. This produces a decompiled version of the class which makes it pretty clear which class it is.

We had an amazingly annoying problem in a Wicket application. A specific user was continuously having problems with ajax controls on pages (search fields, auto-complete fields etc). The problems were caused by PageExpiredExceptions. We couldn’t understand why only this one user had these problems. This went on for ages, until today I found out that Wicket 1.4 sets a default limit of 5 page maps per session. This specific user typically worked with multiple browser tabs on the application and once he went over 5, some of the page maps got evicted and the ajax stuff started failing. The solution was to call “getSessionSettings().setMaxPageMaps(100)” to allow up to 100 page maps per session.