Sometimes its useful in an application to have a list of users who are currently logged onto an application on a server. To do this, you first need a SessionAttributeListener which listens for attributes being added to and removed from the session:

Then from within your application login, you can set a session attribute when a user logs on

You don’t need to remove the attribute on logout, as long as you are invalidating the session – this will automatically remove the attribute and invoke the attributeRemoved method of the listener. The final step is to add an activity monitor display to your application which calls SessionAttributeListener.getActiveUsers() and displays the list.

For someone starting out with Wicket, it can be tricky to figure out basic things like how to display images. Here are basic three scenarios: 1. Simple fixed image – no wicket code required: HTML:

This is fine as long as you don’t need any control over the image. 2. Image set from code: HTML:

JAVA:

The ContextRelativeResource method here tells wicket to load the image from the images folder in your application (the same path as used in the relative src attribute used in the simple HTML example 1). 3. Image set using CSS: HTML:

CSS:

This approach is preferred for images which are really only part of the styling of the application (like[…]