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Re: How Does Language Impact Framework Design?
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Posted: Jan 16, 2008 8:00 AM
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> > You say that Wicket is an excellent web framework...why
> do
> > you have to write things twice? one time in the HTML
> file
> > and one in Java.
> >
> > My company considered Wicket a year ago but we did not
> > choose it because of this problem: we had to write
> things
> > twice.
> >
> > The only solution (that no one has done yet, I don't
> know
> > why) is to completely eliminate all kinds of HTML/XML
> and
> > write web applications in Java only, with a framework
> that
> > mimics a GUI library (i.e. widget trees) but produces
> > HTML/Javascript.
>
> What, exactly, did you have to write twice? You have to
> write a Wicket ID twice -- once in the Java component and
> once as an attribute in the HTML to link the Java with the
> HTML, but that's about it. You do have the option
> sometimes of coding into the HTML sample display elements
> that will be replaced by the Java component, if you want
> to get a more realistic sense of what the page will look
> like once the Java component replaces the sample elements
> with the real once based on the model -- but you don't
> have to do that.
Ok. Let's see some examples. Let's start with the Hello World example.
You have to write the following Java code:
import org.apache.wicket.markup.html.WebPage;
import org.apache.wicket.markup.html.basic.Label;
public class HelloWorld extends WebPage
{
/**
* Constructor
*/
public HelloWorld()
{
add(new Label("message", "Hello World!"));
}
}
And this HTML:
<html>
<body>
<span wicket:id="message" id="message">Message goes here</span>
</body>
</html>
Which is pretty much the same: an HTML page declared twice, once as HTML and once as a label object inside a page object.
Ok, let's go to another example: the GuestBook. The Java code is:
public final class GuestBook extends WebPage
{
/** Use a Vector, as it is synchronized. */
private static final List commentList = new Vector();
private final ListView commentListView;
public GuestBook()
{
add(new CommentForm("commentForm"));
add(commentListView = new ListView("comments", commentList)
{
public void populateItem(final ListItem listItem)
{
final Comment comment = (Comment)listItem.getModelObject();
listItem.add(new Label("date", comment.date.toString()));
listItem.add(new MultiLineLabel("text", comment.text));
}
});
}
public final class CommentForm extends Form
{
private final Comment comment = new Comment();
public CommentForm(final String componentName)
{
super(componentName);
add(new TextArea("text", new PropertyModel(comment, "text")));
}
public final void onSubmit()
{
final Comment newComment = new Comment();
newComment.text = comment.text;
commentList.add(0, newComment);
commentListView.modelChanged();
comment.text = "";
}
}
}
The above code builds a page with a text area, a submit button, and a list of strings.
Then we need this HTML:
<html>
<body>
<form wicket:id = "commentForm">
Add your comment here:
<p>
<textarea wicket:id = "text">This is a comment</textarea>
<p>
<input type = "submit" value = "Submit"/>
</form>
<p>
<span wicket:id = "comments">
<p>
<span wicket:id = "date">1/1/2004</span><br>
<span wicket:id = "text">Comment text goes here.</span>
</p>
</span>
<wicket:remove>
<p>
1/2/2004<br/>
More comment text here.
</p>
</wicket:remove>
</body>
</html>
Which builds again the same thing.
And I am asking you: why? the WebPage object could simply go through all of the components, produce a nice HTML object automatically.
The HTML written above is reduntant.
>
> The solution you suggest (abstract the HTML away
> completely) has indeed been done, see Google Web Toolkit
> (GWT) and also in Echo and (for AJAX) Echo2. However, I
> suspect these have less flexibility than Wicket when it
> comes to customizing the look-and-feel of the pages.
No, it has not been done.
The Google Web Toolkit translates Java code to html/javascript. It is not the Java code that produces the html/javascript.
The Echo2 toolkit (I have worked with it for a project) makes the browser a display server, ala X-Windows, using AJAX techniques. It's slow and complex.
My idea is to preserve the web page concept, complete with navigation, but not to have to write html.
>
> Beyond that, it depends on whether you prefer using HTML
> to customize your look-and-feel versus doing that via API
> method invocations (as when building fat clients in
> Swing). Most people building web applications have
> already made a significant investment in HTML/CSS skills,
> and high-power tools for that are readily available -- so
> you're not locked into using a particular Java IDE to ease
> the painting of GUIs. Furthermore, you may have some
> pre-written HTML portions that you really want to
> incoroprate (e.g. standard page headers, or static pages
> written in HTML by others), and this is probably much
> easier to do in Wicket than in GWT or Echo.
Any html coming from artists or web creators should be converted to Java code that produces the html at run-time. The workflow should be:
raw html -> java code -> compilation -> html with data.
The HTML should be treated like an Qt .ui file, i.e. as a description of the gui.
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