<p>I wonder if there is an example which html files and java files are resides in different folders. </p>

I don't recommend using a separate page directory unless you are quite comfortable with how resource streams work, which I am not.
The vast majority of wicket projects I have seen keep class and html files in the source directory.  I tried separating them myself but then found that getting my hands on other resources, like images and such, was a hassle; so, I wound up putting those resources in the package directory - in the end I had resources in several different places and it was more of a mess than putting everything in package directory would have been.
That said, here's the code I used to put my html templates in a separate folder.  It should be added to Init() in your application class.
```
```
IResourceSettings resourceSettings = getResourceSettings();
resourceSettings.addResourceFolder("pages"); //the full path to your folder, relative to the context root
resourceSettings.setResourceStreamLocator((IResourceStreamLocator) new PathStripperLocator());
```
```
https://cwiki.apache.org/confluence/display/WICKET/Control+where+HTML+files+are+loaded+from
has a tutorial on this.