Page History

...

Another extremely powerful concept is how the message is looked up in the property files. Normally a properties file with the same name as the current component is used. E.g. if you are working within the component SummaryPanel, the message is looked up in the file SummaryPanel_nl_NL.properties (for Dutch, Netherlands locale). If that fails (either because the file does not exist, or because it does not contain the message), file SummaryPanel_nl.properties, and then SummaryPanel.properties are investigated. This is all just like Java's resource bundles work. But of course Wicket goes further. If the message is still not found, the property files of the parent class are investigated, and again, and again, all the way up to java.lang.Object. For each class all locale variants are searched for. If that fails also, the parent component (in the page hierarchy) is used as reference to look up the properties file. The whole search game as described above starts again for this component. Searching continues up the component hierarchy until the page is reached. Finally, the class hierarchy trick is repeated with your application class

Components are reusable, but in order to make it really reusable you should be able to override the messages depending on where the component is used. This is facilitated by first looking up the message (following the algorithm above) for every parent in the component hierarchy (aka page hierarchy). Every component can override the messages of its child components, so the search starts at the page's properties and then trickles down to the component that uses it (yes, its top-down). In order to make overrides specific to a certain child component, you can prefix the message key with the component id of the child. See ComponentStringResourceLoader for more details.

If no message was found in the page hierarchy, another search starts which will look at your application class and its super classes. So Wicket first looks at MyApplication.properties (provided MyApplication is the name of your application) and then up the class hierarchy, passing org.apache.wicket.Application, up to java.lang.Object. This is how Wicket provides its many default i18n texts.

This might sound complicated, but in practice you simply have one properties file per page and some more for components that are reused over multiple pages. For smaller applications you can even put everything in one properties file. These rules work so well that you just do what you think is correct and it almost always just is.

...