In Java, first we had servlets, and each one of them answered to request made to a particular url (or an url matching a particular expression), but it was hard to create pages that way, and it was even harder to create a system composed of many “pages” (note the conceptual jump from servlets answering url requests to "pages”)
Then, JSPs were created, take a look at them and you will see that each JSP page knows nothing about any other, JSP was designed thinking that the best way to deal with many pages was to handle it them as “independent”: lets make each page unaware of what page is next (and what page was previously). Just as servlets were somehow unaware or each other.
After that, JSF was invented, this new technology sees "Pages" as components (composed of other simpler components) forming a component tree. All the components in the same page collaborate to give life to a JSF page (but it does it in a pretty limited way, unless you use Facelets, but they weren't invented until later, and they didn't help much with navigation). By now, we should be far far away from the servlets with which we started... but still each page is unaware of what page is next (and what page was previously). Just as servlets were somehow unaware or each other.
Why?
Then, we got Seam, with its powerful bijection, to help us deal with the job of exchanging information between pages. And its pages.xml files, to help us deal with the limited navigational capabilities available with plain JSF. But still each page is unaware of what page is next (and what page was previously). Just as servlets were somehow unaware or each other.
Why?
In a somewhat parallel universe, perhaps in the Twilight Zone, WebObjects was created, in WebObjects, we have no servlets, "Pages" are components (composed of other simpler components) forming a component tree. All the components in the same page collaborate to give life to a WO page. And if you want, you can treat a WO page as a WO Component, they are pretty much the same thing, at it is trivial to change from one to the other, and create libraries of WO Components (comparatively creating JSF components is so hard that is mind boggling). And each page is aware of what page is next (and what page was previously). Let me state that again: The code in each page is aware of what page is next (and what page was previously). Here is a pseudo code example:
public WOComponent gotoProfilePage(){
ProfilePage profilePage = new ProfilePage();profilePage.setUser(this.getSelectedUser());
return profilePage;
}
And that's it, that is how you send the currently selected user from the current page into the next page, plain and simple, you just create an object of the type of the page where you want to go, and use its getters and setters go share state with it... what could be simpler than that? why I have been unable to find a framework that deals with page navigation like this? Well, you might say, it is not that flexible, what if you want configurable navigation? Well, then you can do it like this:
public WOComponent gotoProfilePage(){
WOComponent profilePage = this.getPageWithName("ProfilePage");profilePage.takeValueForKey(this.getSelectedUser(),"user");
return profilePage;
}
Any page with the name "ProfilePage" that has a "user" attribute will used for this navigation action. So... the question is still in the air... why? why I have been unable to find a web framework that deals with navigation in this way... why? We have frameworks that create dependencies between otherwise only dynamically related stuff, like
Hibernate, creating properties in java objects that mimic the dynamic relations in a database, but we refuse to offer the same services for page navigation... I don't get why... this seems as such a natural way to deal with this kind of problem... is there a disadvantage here that I am not seeing? Or was WebObjects really created in the Twilight Zone?
Update: Just discovered
another disadvantage of xml based navigation in JSF/Seam: It is
not possible to use the java debugger or logging frameworks "out of the box" to debug the conditionals in the xml file, one has to wait for (or build) a custom debugger/logger for JSF/Seam navigation.
