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Is it possible/advisable to run Spring Boot without controllers just for the #ScheduledTasks and ORM?

I'd like to run a Spring Boot service without any of the controller-related stuff. I'd like it to just run a scheduled task every hour and do work if needed. I'm wanting to use Spring Boot, because I already know how to set the Hibernate ORM up, and I'm re-using a lot of the same repositories as another Spring Boot service. So, I spun up a new Spring Boot project and left out the start-web package.
The main issue I'm running into is that despite having a scheduled task set up, the service starts and immediately quits without running the scheduled task. In my head, I imagined the service kind of just sitting there, running, waiting for the time to trigger the scheduled job I have configured and kind of just sleeping until then. Are my expectations bad, or do I just have it misconfigured?

I've solved the problem. It was a configuration issue causing the Spring Boot app to not recognize the presence of required configuration values in the application.properties file.

You can either remove spring-boot-starter-web from your dependencies or in your main class you can configure the SpringApplicationBuilder to not include the web server.
new SpringApplicationBuilder(YourApplication.class)
.web(WebApplicationType.NONE)
.run(args);

Use #EnableScheduling in main class and application won't shuts down.

Spring Boot 2 how to change startup behaviour

do not judge this question) I want to implement WEB installer for my Spring Boot application, and very interesting moment is that my application plays 2 role: Installer and Backend(Application). When i first run my app i need to tell Spring to not initialize particular beans(Hibernate(while startup application must not to be failed to start because database may not exist), ActiveMq and others beans that will be added in installation process) and show some html pages with installation guide. Also i need to prevent access to endpoints where some logic with database occurs. When installation finished i will create new application.properties or some other file with settings and i tell Spring to initialize all required beans with Hibernate, ActiveMQ and others. Maybe i will make restart of application and new behaviour that based on installation will occur. And in next starts my application will not show installation guide. To simplify the question: I need to change startup behaviour of Spring Boot Application. For fun i can give an example with human: I need to make human live with no organs, and this human will live very good, and if i want i can add organs to human and he will be live very well))

You can use #Profile annotation. Check this link: https://www.mkyong.com/spring/spring-profiles-example/

Call method after JBoss deploy

I want to have some method run, only after my WAR has been deployed to JBoss.
The problem: Currently I am using #PostConstruct to load saved schedules from the DB. The problem is that I am creating instances of the Schedulers from this method, which in turn is starting the Quartz schedulers, which is stopping JBoss from completing the deploy.
If there are no schedules to load, my WAR deploys fine, but if there are schedules they are causing the deploy to fail, because JBoss is "waiting" for the schedules to actually complete.
Is there some way to delay the method call until after it is fully deployed?
Or alternatively, is it possible to make Async calls on the Server (from the Server code)?

Java EE specification heavily refrain any thread manipulation outside facility provided by the application server.
You shouldn't in any case use a container manged thread in an infinite loop; the container expect the thread to be returned. Thread creation can still be done without too much collateral damage (if you don't put several apps on the server as the container won't be able to manage the resources between all the applications) but the any container thread must be returned.
In the new Jboss 7 there is some Java EE scheduling facilities (#Scheduling and timer, with possible persistent timer). A quick search show some example how to run Quartz in JBoss 7: How to enable Quartz scheduling in Jboss AS 7.0?
In older JBoss more advanced integration exist (JCA integration is the only standard way to get finer thread management). Use google to find them.

Wouldn't the simple ServletContextListener solve the problem for you? Just implement whatever you need in contextInitialized method.

In JBoss 7, there is a management api.
Maybe you can use it to check if the server is started (with a singleton and a TimerService).
Sample code:
ModelControllerClient client = ModelControllerClient.Factory.create(InetAddress.getByName("localhost"), 9999);
ModelNode op = new ModelNode();
op.get(ClientConstants.OP).set("read-attribute");
op.get(ClientConstants.NAME).set("server-state");
ModelNode returnVal = client.execute(op);
if(StringUtils.equals(returnVal.get("result").toString(), "\"running\"")){
LOGGER.info("Server running, init start actions");
timer.cancel();
}else{
LOGGER.info("Server not running, wait");
}

Deallocation for static class instance variable

This would be my first question, so please if I have not completed the question or left something out do let me know.
Background:
Well I have a Java based web-service and it is serving an iPhone app. It has connection to database and in order to improve the performance I have implemented caching using Memcached. The connector I use is spymemcached.
My question:
I have a static class which has a synchronous connection to the memcached server.
my reference is: http://sacharya.com/using-memcached-with-java/
But when I restart the memcached server or deploy another jar on tomcat I get this error:
The web application appears to have started a thread name [some name] but has failed to stop it. This is very likely to create a memory leak.
So, how do I deallocate the static class before I can restart or redeploy my application on tomcat?
--
Thanks.

The static class is not the problem. That will be unloaded assuming that it is in a JAR in WEB-INF/lib. The problem is the thread. Whatever starts that thread needs to stop it. See this presentation for further details on Tomcat's memory leak prevention and detection:
http://people.apache.org/~markt/presentations/2010-11-04-Memory-Leaks-60mins.pdf

That page implements a Singleton Pattern for MyCache class.
A singleton can't be destroyed.
Maybe you can define a ServletContextListener (or similar Listener in the app server) to stop the thread manually.

Start / stop a web application from itself?

I've made a web application using Java, Struts and running over Apache Server and Tomcat. It would be very useful to be able to restart the application from the web. I don't want to restart Tomcat, only this webapp, the same way as Tomcat Manager does it.
Do you know how can I do it? If not, any way to simulate that behaviour (reload config.properties, make Hibernate init process, etc)?
Thank you a lot.

I took a quick look at the source code for the Tomcat Manager. It looks like there's a class that's part of the Tomcat source called "Container Servlet". From the javadocs:
A ContainerServlet is a servlet
that has access to Catalina internal
functionality, and is loaded from the
Catalina class loader instead of the
web application class loader.
A ContainerServlet automatically gets passed a wrapper that can be used to get the Context and Deployer -- and the Deployer has helpful methods such as start(String contextPath) and stop(String contextPath) that will do what you want.
So, what I think you would need to do is write your own servlet that inherits from ContainerServlet, and configure Tomcat to load your servlet using the Catalina class loader (look at how the Manager is configured to see how). Note that this is probably not going to be an option for you in a hosted environment.
Then your servlet could have, say, a button you press to reload the application. I recommend putting password-protection of some kind in front of that. :)

Just hit the URLs
http://<username>:<password>#<hostname>:<port>/manager/stop?path=/<context path>
to stop and
http://<username>:<password>#<hostname>:<port>/manager/start?path=/<context path>
to start. That simulates you using the manager application.

Tomcat Manager offers an http interface to start/stop an application and other tasks. There are Ant tasks that you can use to easily access these operations.