Please help,

Is it common to have different skilled persons building a web application? A web designer, a web programmer ("integrator" and application logic coder).

I suspect that in l a large projects there will be many people building the "information system" (in the web application and eventually connecting it with the company existing systems).

Is it common to have a web designer to have Java knowledge?

I am doing a academic (6 months) work on a web programming subject, focused on the integration between the application layer and the user interface. And I am searching for some way to get feedback from professionals working in the area.

Appreciate all the help You can give me.

Is it common to have different skilled persons building a web application? A web designer, a web programmer ("integrator" and application logic coder)

It is very common indeed. It is rare that you will find a (real) designer who is a good programmer and vice versa. Good programmers are more logical, linear thinking, most are not creatively gifted in design. The opposite is true for Designers. That's not to say that people who can do both equally well don't exist, they do, but finding someone talented in BOTH areas may be hard.

Is it common to have a web designer to have Java knowledge?

Not in my experience, but you might find a person who does.

For massive web applications they are almost always composed from many programmers and designers each doing their own piece of the app and usually they combine it all in the end threw include files or they each do one portion of the site with the designer putting it together in the site.

Yes, different people all have different skills. Depending on the size of the project you might typically find several disciplines carried out by various people, such as

Back end programming/scripting - PHP, ASP, .NET, Java etc
Web designers - (x)HTML, CSS, Javascript
Graphic design - logos, branding, misc site images

and then you may have other roles...

Sales/Customer liaison
Project manager
Copywriters
Marketing

and so on, the bigger the project the more people involved.

Sorry for the long post,

Thank you all for replying,

Assuming that the most common development teams consist in collaborating web designers and web programmers. The first group responsible for building the looks and user interaction, and the second for wiring the user interaction with the code, writing fast and robust, functional code, and in some cases implementing some advanced user interaction (with AJAX like pages).

In your opinion, what are the harder problems to resolve when collaborating from the designer point of view? and from the programmer point of view?

In my opinion:

From the web designer point of view.
It will build up a functional prototype of the site, something that gives the look-and-feel of the including the base HTML/CSS/JS.
Problem comes next. The work is ready and join their pieces. After it a change is needed (they merged there work to soon, or that a change was requested after release).
From the moment the programmer wires the pages to the code, the designer will have some difficulties in working with the "programmer changed" prototype.
All changes from there on will have to be made with the programmer, after all he is the one that understands fully the impact that some "minor" changes can do.
I am assuming that the work of the programmer is intrusive in the work of the web designer. Something like changing the HTML files extension to JSP and inserting java scriptlets, or changing input elements to struts tags, aspx controls, or some other thing.

From the web programmer point of view.
It will build back-end code, something that performs the actions need, assuming proper input is available, and gets the resulting output. And it haves to think state management, input validation, authentication eventually with different roles. And still has to hurry about things from the user interface, especially if after testing the application with real data, in the first prototype the data was fixed and probably not representative.

What is your opinion?