Develop Reference

What is Vaadin UI and how to navigate between UI's

First question: I am trying to create web app using Vaadin 8.3.1 but I am struggling to understand concept of the UI class. I was reading docs but still I can not somehow understand it. I thought that it is just a basic web page which is currently displayed but I am not sure about that definition. So my question is what exactly is UI, how can I navigate between UI's, when to use view and when to use UI ?
Second question: I was reading docs about navigation between views but I was not able to display anything. In UI all we have to do is to setContent and that is it. But what about Views ? How can I display something using views ?
Thanks for any help !

The basic concept of Vaadin is to create single page web applications. The UI class is the root of the dynamic web page, which has changing content, the views. So typical Vaadin application does not consist of multiple UI's, but single one. (It can have many, but I said typical)
One UI can thus have many views. Usually in main UI you set root content, a main layout that consist of menu and content container (a layout) for Views. When Navigator is setup, it is given that content holder, and then based on navigation Navigator will be placing the views to content area. This is described in detail here:
https://vaadin.com/docs/v8/framework/advanced/advanced-navigator.html
Apparently you want to integrate Spring with Vaadin, and for this you need Vaadin Spring add-on. The documentation is here:
https://vaadin.com/docs/v8/framework/advanced/advanced-spring.html
To get most out of the documentation, you need example application, which you and inspect and play with. On Vaadin web page, there is full stack functional demo application, which demonstrates application architecture made with Vaadin + Spring.
https://vaadin.com/start/v8-full-stack-spring

Multi Windowing on a Java Web project

I have an EJB 2.1 Project (Actually, it must be migrated into EJB 3.1 :-)) Currently it supports only one window. it means the user should work on a window. It is because of the variables, used as session variables. (Last Search Criteria, last used id, etc...).
I want to make it possible to open two or more tabs in for example Firefox and work parallel. If the user is on the same tab, the variables should be kept only for that tab. Only global variables can be valid for all tabs.
How can i approach to this problem.??
Any documentation to understand multiwindow will be also helpful.
Or any other idea or experiences about multiwindow web project is also welcome.

There isn't any built-in way to deal with this in either browsers or any EJB that I am aware of. Other web app frameworks have the concept of Web Flows that are series of connected actions that can handle multiple flows in different tabs of the same browsers, so you may wish to start looking there.
In a nutshell, they create their own "cookies" that the application controls, not the browser itself. These "application cookies" are then used to stash chunks of information related to the current set of operations, much like a session.
These sorts of things are often kicked off by the user clicking a link that opens in a "new window" (or tab) that notifies the application (via a page hit or an ajax call) that a new "work session" is being opened and gets the inner-session set up.

show or hide a portlet based on the event of another portlet

I m new in Liferay portlet. Can any one tell me how I can show or hide a portlet based on the event of another portlet. I want coding in ice:spaces only not any other way. If someone know solution for this please reply me as soon as possible.
Note: I m using ice:spaces in xhtml not .jsp file.
Thank you.

If you're using standard portlet technology this is not possible in a direct way. If using JSR 286 (Portlet 2.0) you could send an event (or a public render parameter) so that the portlet you want to hide can set its window state to minimized (you still see the title). Alternatively you could set the window state of the portlet requesting to hide others to maximized, this would hide all other portlets.

JSF table component with high demo value

As part of an ongoing quest for a nice web demo in a couple of weeks we now have a list of customers where we are considering presenting an HTML table with a row of core details for each, and then allowing the user to ask for additional details.
This could be in a mouse over, an opening up the table inserting a panel of details, or opening a popup window. Right now I am looking for a JSF table component optimized for ooh-aah-value doing one or more of the above. Until now I've stayed with the core JSF components, and the h:dataTable is functional but rather un-oohaahish.
I'd appreciate suggestions. Links to videopresentations are appreciated even more :)
(Note: I'm using the latest Mojarra, so JSF 2.0 is fine)
EDIT: To wrap things up: We went with OpenFaces 3.0EA2 for the web demo with very nice visual results, but found that the documentation for getting up and running with the full bells and whistles is simply not there and there is too much pixie dust. We ended adjusting the existing demo (which is extremely impressive) to deal with our data instead.

OK, oohaahishness requires a good shot of CSS. This is indeed not included in the standard JSF implementation. So, you'd like to look for a component library which includes CSS skins/themes. They usually have a component showcase at their homepage. There are several:
PrimeFaces - Datatable component demo - Theme gallery
OpenFaces - Datatable component demo
RichFaces - Datatable component demo
IceFaces - Component showcase, check Table (URL is not bookmarkable)

Supporting BalusC's answer, I will add that PrimeFaces lab table demo even have new features.
In order to use the jar, download the lab showcase demo and open the war from your IDE (e.g. eclipse). You will see how to use it.

Adding Help Contents, Search Help using Command Framework

My colleagues and I are building a new RCP application and trying to find our footing in RCP. My coworker managed to get the Eclipse Help framework working pretty quickly - but he used the old style Actions and ActionBarAdvisor.makeActions() to do it. All of the RCP Menu creation tutorials I've read (the ones that were written post Eclipse 3.3 anyway) advocate depreciating Actions and switching over completely to Commands. So I'm trying to do this. However, I cannot get the help Commands to work - not without using the help actions.
Specifically, I'm attempting to figure out how to add the default Eclipse help menu commands org.eclipse.ui.help.helpContents and org.eclipse.ui.help.helpSearch to my help menu. I've created the menu contribution, and added the commands. But they remain greyed out. I can't find any mention of anything else I have to do to hook them up to the help framework my coworker had working before using actions. If I add the actions for them and register them in make Action, they still work. But I'm trying to do this without Actions. How is this done? What am I not doing?

According to the Command tutorial on vogella.de some common commands need some ActionFactories registered:
Standard commands sometimes map to actions which are contributed via ActionFactory in the class ApplicationActionBarAdvisor. If the ActionFactory returns an IAction you need to register this action. If not these commands are inactive in your menu. For example the following made the reset perspective and welcome command active.
I think, this might be the case with the Help command as well - but I have not tested it. The other possibility would be that there is no enabled handler for the command...