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Map spring rest controller to a path without the servlet context

I have a spring boot application with the following context path:
server.servlet.context-path:/api
I need to write a rest controller that's mapped to
http://localhost:8080/logout
instead of http://localhost:8080/api/logout
Is there a way to achieve this? changing the "server.servelt.context-path" value is not an option.
this is what I tried and didn't work:
#GetMapping(value="../signout"){
public void logout(){
}

Nero, you say you can't change the "server.servlet.context-path" value. I bet you say this because you don't want to break the API, but I think you can manage to change this without breaking the API. Set the context-path to blank, which is permitted. Then in your application change the "api" mapping, which I assume is currently "/", to "api".
Change server.servlet.context-path:/api to server.servlet.context-path:/ or maybe server.servlet.context-path: (no slash). (Supposedly this is the default so you might just remove this entry altogether.)
Somewhere in your application change #RequestMapping("/") to #RequestMapping("/api").
Now you can also have #GetMapping(value="/signout") and you will have resources at http://localhost:8080/logout and http://localhost:8080/api.
I don't know what mapping annotations you happen to be using, but hopefully this is clear enough.

It may not be possible within that application to go outside its context root. Maybe you can create a separate Rest service app for that particular url and take it from there.

Accessing a Filter object through a WebApplicationContext

I want to call a method on a Filter object after it has been added according to the web.xml definition. All I got is a WebApplicationContext object (let's call it: wac).
I'm able to add new Filter objects via: wac.getServletContext().addFilter("otherfilter", otherFilter);
Also, I can test successfully for its existence via: wac.getServletContext().getFilterRegistration("myfilter")
But how may I access (and possibly modify) Filter objects which have been added before?

I'm not sure how to do it exactly as you want, but this problem is usually solved using different approach.
You can declare your Filter as a bean in your application context and then register a DelegatingFilterProxy in web.xml to delegate filtering to your filter.
In this case your filter will be a regular Spring bean, and you'll be able to access it like any other bean.

The Servlet API does not provide any mechanism to directly access a Filter instance once it has been added to a ServletContext. The best you are going to get with the Servlet API is the FilterRegistration interface you have already found which lets you modify the same set of configuration options as you can via web.xml.
Depending on exactly what you want to do, you might be able to code your way around this problem using init parameters but that is never going to be a particularly clean solution. I'd go with the DelegatingFilterProxy solution suggested by axtavt.

How to add request parameter in jsf2?

In my app, before upgrading to jsf 2, when doing a custom redirect I used to manually put a request parameter with a specific value in external context like this:
FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap()
.put(CmwNavigationControllerBean.PARAM_DISPLAY_TARGET_POPUP, "true");
Now this line, throws an exception because it seems that this map is no longer allowed to be modified:
at java.util.Collections$UnmodifiableMap.put(Unknown Source) [rt.jar:1.7.0]
Isn't really no other way to bypass this exception? I'm doing refactoring because of upgrade and I try to keep the changes at minimal level.

You can either use a view parameter or use the flash scope for that. A view parameter is in practice a GET parameter which you can pass when you request the page you want to redirect to. For your case, you should redirect to it with the parameter appended.
Return the navigation case with the parameter appended:
//Will be reflected in browser's address bar as /context/myDestinationView.xhtml?displayTargetPopUp=true
return "myDestinationView?displayTargetPopUp=true&faces-redirect=true&includeViewParams=true";
Catch it from your destination view:
<f:viewParam name="displayTargetPopUp" value="#{displayTargetPopUp}" />
Another way if you want to avoid including it in your GET request, is to use flash scope, which is supposed to be fixed for Mojarra 2.1.27 and 2.2.5 versions. Flash scoped values are designed to support a redirection, while the request ones are not.
See also:
Understand Flash Scope in JSF2
How do you pass view parameters when navigating from an action in JSF2?

Rather than getRequestParameterMap() (which is read-only) you should invoke getRequestMap() on the ExternalContext.
For example:
FacesContext.getCurrentInstance()
.getExternalContext()
.getRequestMap()
.put(CmwNavigationControllerBean.PARAM_DISPLAY_TARGET_POPUP, "true");

How to invoke local RESTLET resource without full url?

I need to retrieve a list of given entities (apples) from another resource (fruitDelaer) I know I can do smt like this (somewhere in my fruitDealer resource implementation):
ClientResource applesResource = new ClientResource("http://localhost:8888/fruitShop/apples");
Representation response = applesResource.get();
But since this 'apples' resource is local to the one it's invoking it, is there a way not to specify the full url?
NOTE: I suspect this may have more to do with Java itself than restlet

Restlet offers the RIAP pseudo-protocol (Restlet Internal Access Protocol), which lets you do exactly that, invoke resources local to your application|virtual host|component using an URI such as "riap://application/fruitShop/apples".
Additional details here.

I would consider another approach. A Service that you could call from fruitDealer to retrieve what you need. There is a lot of work to be done creating objects and such that is not necessary.

JSF & Facelets Flow

I have a dynamic Facelets page that needs to show information from database when the page loads. At this point in the flow, there have not been any form submissions. Every JSF example I can find only shows a form submission with dynamic results on the next page.
Every call I make to our database is currently takes place after an action has been triggered by a form submission. Where should this code go if there hasn't been a form submission, and how do I trigger it? A code snippet would really help me out!

You should be able to do your initialization work in the constructor (or lazily in one of your accessors) of your managed bean.

If you're using Spring integration (see here also), it's easy.
In your backing bean, simply use something like:
public class BackingBean implements InitializingBean
{
public void afterPropertiesSet()
{
loadInitialData();
}
}
If you're not integrating with Spring there are two options:
Load the initial data in the class constructor;
In your faces-config.xml, you can set properties to be injected. Properties are guaranteed to be set in the order they're specified in the config file. So, just create a dummy property and then within that method load up your default data. i.e. create a method public void setLoaded(boolean loaded) { loadInitialData(); }, and in your faces-config.xml have 'loaded' being set as a property on that backing bean.
Hope this is all clear!

You write (with my emphasis added):
Every call I make to our database is currently takes place after an action
has been triggered by a form submission. Where should this code go
if there hasn't been a form submission, and how do I trigger it? A
code snippet would really help me out!
It sounds to me that you want to retrieve information from the database prior to form submission.
It seems to me that you want to make an Ajax call to query the database. The Ajax call can fire on a different event than the form submisson event. This will probably entail using Javascript rather than the Faces framework.