I'm working with very large JSF/Facelets applications which use Spring for DI/bean management.
My applications have modular structure and I'm currently looking for approaches to standardize the modularization.
My goal is to compose a web application from a number of modules (possibly depending on each other). Each module may contain the following:
Classes;
Static resources (images, CSS, scripts);
Facelet templates;
Managed beans - Spring application contexts, with request, session and application-scoped beans (alternative is JSF managed beans);
Servlet API stuff - servlets, filters, listeners (this is optional).
What I'd like to avoid (almost at all costs) is the need to copy or extract module resources (like Facelets templates) to the WAR or to extend the web.xml for module's servlets, filters, etc. It must be enough to add the module (JAR, bundle, artifact, ...) to the web application (WEB-INF/lib, bundles, plugins, ...) to extend the web application with this module.
Currently I solve this task with a custom modularization solution which is heavily based on using classpath resources:
Special resources servlet serves static resources from classpath resources (JARs).
Special Facelets resource resolver allows loading Facelet templates from classpath resources.
Spring loads application contexts via the pattern classpath*:com/acme/foo/module/applicationContext.xml - this loads application contexts defined in module JARs.
Finally, a pair of delegating servlets and filters delegate request processing to the servlets and filters configured in Spring application contexts from modules.
Last days I read a lot about OSGi and I was considering, how (and if) I could use OSGi as a standardized modularization approach. I was thinking about how individual tasks could be solved with OSGi:
Static resources - OSGi bundles which want to export static resources register a ResourceLoader instances with the bundle context. A central ResourceServlet uses these resource loaders to load resources from bundles.
Facelet templates - similar to above, a central ResourceResolver uses services registered by bundles.
Managed beans - I have no idea how to use an expression like #{myBean.property} if myBean is defined in one of the bundles.
Servlet API stuff - use something like WebExtender/Pax Web to register servlets, filters and so on.
My questions are:
Am I inventing a bicycle here? Are there standard solutions for that? I've found a mentioning of Spring Slices but could not find much documentation about it.
Do you think OSGi is the right technology for the described task?
Is my sketch of OSGI application more or less correct?
How should managed beans (especially request/session scope) be handled?
I'd be generally grateful for your comments.
What you're aiming to do sounds doable, with a few caveats:
The View Layer: First, your view layer sounds a little overstuffed. There are other ways to modularize JSF components by using custom components that will avoid the headaches involved with trying to create something as dramatic as late-binding managed beans.
The Modules Themselves: Second, your modules don't seem particularly modular. Your first bullet-list makes it sound as if you're trying to create interoperable web apps, rather than modules per se. My idea of a module is that each component has a well-defined, and more or less discrete, purpose. Like how ex underlies vi. If you're going down the OSGi route, then we should define modular like this: Modular, for the sake of this discussion, means that components are hot-swappable -- that is, they can be added and removed without breaking the app.
Dependencies: I'm a little concerned by your description of the modules as "possibly depending on each other." You probably (I hope) already know this, but your dependencies ought to form a directed acyclic graph. Once you introduce a circular dependency, you're asking for a world of hurt in terms of the app's eventual maintainability. One of the biggest weaknesses of OSGi is that it doesn't prevent circular dependencies, so it's up to you to enforce this. Otherwise your dependencies will grow like kudzu and gradually choke the rest of your system's ecosystem.
Servlets: Fuhgeddaboudit. You can't late-bind servlets into a web app, not until the Servlet 3.0 spec is in production (as Pascal pointed out). To launch a separate utility servlet, you'll need to put it into its own app.
OK, so much for the caveats. Let's think about how this might work:
You've defined your own JSF module to do... what, exactly? Let's give it a defined, fairly trivial purpose: a login screen. So you create your login screen, late-bind it using OSGi into your app and... then what? How does the app know the login functionality is there, if you haven't defined it in your .jspx page? How does the app know to navigate to something it can't know is there?
There are ways to get around this using conditional includes and the like (e.g., <c:if #{loginBean.notEmpty}>), but, like you said, things get a little hairy when your managed loginBean exists in another module that may not have even been introduced to the app yet. In fact, you'll get a servlet exception unless that loginBean exists. So what do you do?
You define an API in one of your modules. All the managed beans that you intend to share between modules must be specified as interfaces in this API layer. And all your modules must have default implementations of any of these interfaces that they intend to use. And this API must be shared between all interoperable modules. Then you can use OSGi and Spring to wire together the specified beans with their implementation.
I need to take a moment to point out that this is not how I would approach this problem. Not at all. Given something like as simple as a login page, or even as complicated as a stock chart, I'd personally prefer to create a custom JSF component. But if the requirement is "I want my managed beans to be modular (i.e., hot-swappable, etc)," this is the only way I know to make it work. And I'm not even entirely sure it will work. This email exchange suggests that it's a problem that JSF developers have only just started to work on.
I normally consider managed beans to be part of the view layer, and as such I use them only for view logic, and delegate everything else to the service layer. Making managed beans late-binding is, to my mind, promoting them out of the view layer and into the business logic. There's a reason why all those tutorials are so focused on services: because most of the time you want to consider what it would take for your app to run "headless," and how easy it would be to "skin" your view if, for instance, you wanted it to run, with all its functionality, on an Android phone.
But it sounds like a lot of what you're working with is itself view logic -- for instance, the need to swap in a different view template. OSGi/Spring should be able to help, but you'll need something in your app to choose between available implementations: pretty much what OSGi's Service Registry was built to do.
That leaves static resources. You can modularize these, but remember, you'll need to define an interface to retrieve these resources, and you'll need to provide a default implementation so your app doesn't choke if they're absent. If i18n is a consideration, this could be a good way to go. If you wanted to be really adventurous, then you could push your static resources into JNDI. That would make them completely hot-swappable, and save you the pain of trying to resolve which implementation to use programmatically, but there are some downsides: any failed lookup will cause your app to throw a NamingException. And it's overkill. JNDI is normally used in web apps for app configuration.
As for your remaining questions:
Am I inventing a bicycle here? Are there standard solutions for that?
You are, a little. I've seen apps that do this kind of thing, but you seem to have stumbled into a fairly unique set of requirements.
Do you think OSGi is the right technology for the described task?
If you need the modules to be hot-swappable, then your choices are OSGi and the lighter-weight ServiceLocator interface.
Is my sketch of OSGI application more or less correct?
I can't really tell without knowing more about where your component boundaries are. At the moment, it sounds like you may be pushing OSGi to do more than it is capable of doing.
But don't take my word for it. I found other reading material in these places.
And since you ask about Spring Slices, this should be enough to get you started. You'll need a Git client, and it looks like you'll be training yourself on the app by looking through the source code. And it's very early prototype code.
I am facing the same problems in my current project. In my opinion, OSGi is the best and cleanest solution in terms of standards and future support, but currently you may hit some problems if you try using it in a web application:
there is no well integrated solution between a Web Container and the OSGi platform yet.
OSGi may be too much for a custom build web application that is just searching for a simple modularized architecture. I would consider OSGi if my project needs to support third party extensions that are not 100% under our control, if the project needs hot redeployments, strict access rules between plugins, etc.
A custom solution based on class loaders and resource filters seems very appropriate for me.
As an example you can study the Hudson source code or Java Plug-in Framework (JPF) Project(http://jpf.sourceforge.net/).
As about extending the web.xml, we may be lucky with the Servlet 3.0 specification(http://today.java.net/pub/a/today/2008/10/14/introduction-to-servlet-3.html#pluggability-and-extensibility).
The "web module deployment descriptor fragment" (aka web-fragment.xml) introduced by the Servlet 3.0 specification would be nice here. The specification defines it as:
A web fragment is a logical
partitioning of the web app in such a
way that the frameworks being used
within the web app can define all the
artifacts without asking devlopers to
edit or add information in the
web.xml.
Java EE 6 is maybe not an option for you right now though. Still, it would to be the standardized solution.
Enterprise OSGi is a fairly new domain so dont think you will get a solution that directly satisfies your need. That said one of the things I found missing from Equinox (osgi engine behind eclipse and hence one with largest user base!) is a consistent configuration / DI service. In my project recently we had some similar needs and ended building a simple configuration osgi service.
One of the problems which will be inherent to modular applications would be around DI, as the module visibility could prevent class access in some cases. We got around this using a registered-buddy policy, which is not too ideal but works.
Other than configuration, you can take a look at the recently released Equinox book for guidance on using OSGi as base for creating modular applications. The examples may be specific to Equinox, but the principles would work with any OSGi framework. Link - http://equinoxosgi.org/
You should look into Spring DM Server (it's being transitioned to Eclipse Virgo but that's not been released yet). There's a lot of good things in the recent OSGi enterprise spec which has also just been released.
Some of the Spring DM tutorials will help, I'd imagine. But yes, it's possible to have both resources and classes loaded from outside the web bundle using standard modularity. In that, it's a good fit.
As for the session context - it gets handled as you would expect in a session. However, you might run into problems with sharing that session between web bundles to the extent that in not sure if it's even possible.
You could also look to have a single web bundle and then use e.g. the Eclipse extension registry to extend the capabilities of you web app.
Related
I´m working in the design of a java web application capable of executing custom code or precompiled classes uploaded by the users, focused mostly in simple validations of datasets.
The custom class must be constrained to a predefined interface and only some libraries and classes must be available to the custom class.
My first solution is to use a custom Classloader capable of loading .jar files from a defined directory in the file system. This approach seems to work but i´m concerned about the security and compatibility of this solution.
Is possible to limit the classes that can be imported by the custom class and run the code in a sandbox in order to avoid some actions like opening files or sockets?
When the loaded class will be unloaded?
application Servers like Weblogic have some restriction about using custom classloaders?
I have evaluated another solutions like OSGi Bundles, but it looks really complex and the support is limited in some applications server also i´m not really sure if OSGi is the right technology for this particular usage. Embedded Scripting Languages like Groovy o Javascript are discarded because the project owner wants the custom code precompiled and written in Java.
What would you recommend for this problem?
OSGi is a good fit for an application that wishes to accept external code (plugins). All the requirements you mention (predefined interfaces, loading jars, mutiple classloaders) are all covered by OSGi services and bundle management. Bundles can be installed, started, stopped, uninstalled, etc, including in runtime.
OSGi support in web application servers is not really that limited. You could even considered embedding an OSGi framework.
Security-wise you will need a solution around security managers.
I am a junior java developer.
I have to make a project that requires me to have 2 kind of users, managers and normal ones.
The manager may add new duties to the normal users, register new users in the system, view everything etc.
The normal users can only view information related with them.
I am able to do this by my own but I am required to use MVC architecture and I am a little confused.
Please if anyone know where can I find any similar project it will help me a lot
I think the best you can do is use Struts framework to implement your application (http://struts.apache.org/). Simple, universally used, realizes MVC pattern in a very easy and understandable way, supports user handling and so on.
If, on the other hand, you are not allowed to use frameworks...
Well you should struct your application with jsp, servlets and POJOs in order to implement MVC custom. JSPs just handle page layout, Servlets manage navigation and general application control and POJOs (Plain Old Java Objects) realize your business logic, in order to keep in separated layers the "look", the navigation issues and the business.
You don't provide a lot of context but judging by your tags (which include JSP and Servlet) then consider taking a look at the Web application technology stack project AppFuse. It will generate a Web Application project for you using Maven, the project builds on top of the state-of-the-art in Web Development. The generated project has exactly the functionality you are [vaguely] describing.
First some background:
I'm working on some webapp prototype code based on Apache Sling which is OSGI based and runs on Apache Felix. I'm still relatively new to OSGI even though I think I've grasped most concepts by now. However, what puzzles me is that I haven't been able to find a "full" dependency injection (DI) framework. I've successfully employed rudimentary DI using Declarative Services (DS). But my understanding is that DS are used to reference -- how do I put this? -- OSGI registered services and components together. And for that it works fine, but I personally use DI frameworks like Guice to wire entire object graphs together and put objects on the correct scopes (think #RequestScoped or #SessionScoped for example). However, none of the OSGI specific frameworks I've looked at, seem to support this concept.
I've started reading about OSGI blueprints and iPOJO but these frameworks seem to be more concerned with wiring OSGI services together than with providing a full DI solution. I have to admit that I haven't done any samples yet, so my impression could be incorrect.
Being an extension to Guice, I've experimented with Peaberry, however I found documentation very hard to find, and while I got basic DI working, a lot of guice-servlet's advanced functionality (automatic injection into filters, servlets, etc) didn't work at all.
So, my questions are the following:
How do declarative services compare to "traditional" DI like Guice or Spring? Do they solve the same problem or are they geared towards different problems?
All OSGI specific solutions I've seen so far lack the concept of scopes for DI. For example, Guice + guice-servlet has request scoped dependencies which makes writing web applications really clean and easy. Did I just miss that in the docs or are these concerns not covered by any of these frameworks?
Are JSR 330 and OSGI based DI two different worlds? iPOJO for example brings its own annotations and Felix SCR Annotations seem to be an entirely different world.
Does anybody have experience with building OSGI based systems and DI? Maybe even some sample code on github?
Does anybody use different technologies like Guice and iPOJO together or is that just a crazy idea?
Sorry for the rather long question.
Any feedback is greatly appreciated.
Updates
Scoped injection: scoped injection is a useful mechanism to have objects from a specific lifecycle automatically injected. Think for example, some of your code relies on a Hibernate session object that is created as part of a servlet filter. By marking a dependency the container will automatically rebuild the object graph. Maybe there's just different approaches to that?
JSR 330 vs DS: from all your excellent answers I see that these are a two different things. That poses the question, how to deal with third party libraries and frameworks that use JSR 330 annotations when used in an OSGI context? What's a good approach? Running a JSR 330 container within the Bundle?
I appreciate all your answers, you've been very helpful!
Overall approach
The simplest way to have dependency injection with Apache Sling, and the one used throughout the codebase, is to use the maven-scr-plugin .
You can annotate your java classes and then at build time invoke the SCR plugin, either as a Maven plugin, or as an Ant task.
For instance, to register a servlet you could do the following:
#Component // signal that it's OSGI-managed
#Service(Servlet.class) // register as a Servlet service
public class SampleServlet implements Servlet {
#Reference SlingRepository repository; // get a reference to the repository
}
Specific answers
How do declarative services compare to "traditional" DI like Guice or Spring? Do they solve the same problem or are they geared towards different problems?
They solve the same problem - dependency injection. However (see below) they are also built to take into account dynamic systems where services can appear or disappear at any time.
All OSGI specific solutions I've seen so far lack the concept of scopes for DI. For example, Guice + guice-servlet has request scoped dependencies which makes writing web applications really clean and easy. Did I just miss that in the docs or are these concerns not covered by any of these frameworks?
I haven't seen any approach in the SCR world to add session-scoped or request-scoped services. However, SCR is a generic approach, and scoping can be handled at a more specific layer.
Since you're using Sling I think that there will be little need for session-scoped or request-scoped bindings since Sling has builtin objects for each request which are appropriately created for the current user.
One good example is the JCR session. It is automatically constructed with correct privileges and it is in practice a request-scoped DAO. The same goes for the Sling resourceResolver.
If you find yourself needing per-user work the simplest approach is to have services which receive a JCR Session or a Sling ResourceResolver and use those to perform the work you need. The results will be automatically adjusted for the privileges of the current user without any extra effort.
Are JSR 330 and OSGI based DI two different worlds? iPOJO for example brings its own annotations and Felix SCR Annotations seem to be an entirely different world.
Yes, they're different. You should keep in mind that although Spring and Guice are more mainstream, OSGi services are more complex and support more use cases. In OSGi bundles ( and implicitly services ) are free come and go at any time.
This means that when you have a component which depends on a service which just became unavailable your component is deactivated. Or when you receive a list of components ( for instance, Servlet implementations ) and one of them is deactivated, you are notified by that. To my knowledge, neither Spring nor Guice support this as their wirings are static.
That's a great deal of flexibility which OSGi gives you.
Does anybody have experience with building OSGI based systems and DI? Maybe even some sample code on github?
There's a large number of samples in the Sling Samples SVN repository . You should find most of what you need there.
Does anybody use different technologies like Guice and iPOJO together or is that just a crazy idea?
If you have frameworks which are configured with JSR 330 annotations it does make sense to configure them at runtime using Guice or Spring or whatever works for you. However, as Neil Bartlett has pointed out, this will not work cross-bundles.
I'd just like to add a little more information to Robert's excellent answer, particularly with regard to JSR330 and DS.
Declarative Services, Blueprint, iPOJO and the other OSGi "component models" are primarily intended for injecting OSGi services. These are slightly harder to handle than regular dependencies because they can come and go at any time, including in response to external events (e.g. network disconnected) or user actions (e.g. bundle removed). Therefore all these component models provide an additional lifecycle layer over pure dependency injection frameworks.
This is the main reason why the DS annotations are different from the JSR330 ones... the JSR330 ones don't provide enough semantics to deal with lifecycle. For example they say nothing about:
When should the dependency be injected?
What should we do when the dependency is not currently available (i.e., is it optional or mandatory)?
What should we do when a service we are using goes away?
Can we dynamically switch from one instance of a service to another?
etc...
Unfortunately because the component models are primarily focused on services -- that is, the linkages between bundles -- they are comparatively spartan with regard to wiring up dependencies inside the bundle (although Blueprint does offer some support for this).
There should be no problem using an existing DI framework for wiring up dependencies inside the bundle. For example I had a customer that used Guice to wire up the internal pieces of some Declarative Services components. However I tend to question the value of doing this, because if you need DI inside your bundle it suggests that your bundle may be too big and incoherent.
Note that it is very important NOT to use a traditional DI framework to wire up components between bundles. If the DI framework needs to access a class from another bundle then that other bundle must expose its implementation details, which breaks the encapsulation that we seek in OSGi.
I have some experience in building applications using Aries Blueprint. It has some very nice features regarding OSGi services and config admin support.
If you search for some great examples have a look at the code of Apache Karaf which uses blueprint for all of its wiring.
See http://svn.apache.org/repos/asf/karaf/
I also have some tutortials for Blueprint and Apache Karaf on my website:
http://www.liquid-reality.de/display/liquid/Karaf+Tutorials
In your environment with the embedded felix it will be a bit different as you do not have the management features of Karaf but you simply need to install the same bundles and it should work nicely.
I can recommend Bnd and if you use Eclipse IDE sepcially Bndtools as well. With that you can avoid describing DS in XML and use annotations instead. There is a special Reference annotation for DI. This one has also a filter where you can reference only a special subset of services.
I am using osgi and DI for current my project, I've choosed gemini blueprint because it is second version of SPRING DYNAMIC MODULES, Based on this information I suggest you to read Spring Dynamic Modules in Action. This book will help you to understand some parts and points how to build architecture and why is it good :)
Running into a similar architecture problem here - as Robert mentioned above in his answer:
If you find yourself needing per-user work the simplest approach is to
have services which receive a JCR Session or a Sling ResourceResolver
and use those to perform the work you need. The results will be
automatically adjusted for the privileges of the current user without
any extra effort.
Extrapolating from this (and what I am currently coding), one approach would be to add #param resourceResolver to any #Service methods so that you can pass the appropriately request-scoped object to be used down the execution chain.
Specifically we've got a XXXXService / XXXXDao layer, called from XXXXServlet / XXXXViewHelper / JSP equivalents. So managing all of these components via the OSGI #Service annotations, we can easily wire up the entire stack.
The downside here is that you need to litter your interface design with ResourceResolver or Sessions params.
Originally we tried to inject ResourceResolverFactory into the DAO layer, so that we could easily access the session at will via the factory. However, we are interacting with the session at multiple points in the hierarchy, and multiple times per request. This resulted in session-closed exceptions.
Is there a way to get at that per-request ResourceResolver reliably without having to pass it into every service method?
With request-scoped injection on the Service layers, you could instead just pass the ResourceResolver as a constructor arg & use an instance variable instead. Of course the downside here is you'd have to think about request-scope vs. prototype-scope service code and separate out accordingly.
This seems like it would be a common problem where you want to separate out concerns into service/dao code, leaving the JCR interactions in the DAO, analogous to Hibernate how can you easily get at the per-request Session to perform repo operataions?
I'm currently using Java & Spring (MVC) to create a webapp, and I'm considering moving to Grails. I'd appreciate feedback/insight on the following:
I have multiple application contexts in the current Java/Spring webapp that I load through the web.xml ContextLoaderListener; is it possible to have multiple application contexts in Grails? If, yes, how?
This webapp extensively uses a CXF restful web service and the current Java/Spring webapp uses the bundled CXF HTTP client. Can I continue to use the (Java) CXF HTTP Client in Grails?
I implemented Spring Security using a custom implementation of UserDetails and UserDetailsService, can I re-use these implementations in Grails "as is" or must I re-implement them?
There is an instance where I've relied on Spring's jdbc template (rather than the available ORM) and an additional data source I defined in app context, can I re-use this in Grails?
I plan on using Maven as the project management tool; are there any issues of using Maven with Grails where there is a combination of groovy and java?
Edit:
I'm considering moving to Grails to make the development of the web component of the webapp "faster," a la Ruby-on-Rails. Also, I'm considering Grails rather than say Ruby-on-Rails, because I want to continue to use the JVM and I've dabbled with Grails in the past and it was fairly easy to pick-up and use.
Probably. Grails uses a sub-class of Spring's ContextLoaderListener class which it configures in the web.xml file. I can answer more precisely if you let me know how you do it with Spring MVC.
Yes. You might even be interested in the CXF plugin, although I can't vouch for it:
http://grails.org/plugin/cxf
You should be able to use them as-is. However, you might want to check whether this is easily done with the Spring Security plugin. I believe it is, but you'll be able to get a definitive answer from Burt Beckwith, the author of the plugin.
Yes. You can also get hold of the Hibernate session factory to do raw Hibernate stuff. GORM can also work with multiple data sources:
http://grails.org/plugin/datasources
Another Burt Beckwith one :)
It depends on what you mean by "a combination of Groovy and Java". You can build Grails projects with Maven, but the integration isn't entirely smooth. If you have Java and Groovy in your Grails project, then that's taken care of automatically.
In response to Bozho, I use standard Grails services + GORM and wouldn't do it any other way. Note that if you use Java for services and the domain model, you won't have automatic reloading of services. You also lose the benefits of expressiveness and conciseness that Groovy bring.
If you want, you can use static types in Grails services to make it easier for your IDE to provide code completion. It can also give you hints on properties and methods it doesn't recognise (which would corresponding to Java compilation errors). That said, even if you use static types, Groovy can't do type checks at compilation time. You'll only find out about them at runtime.
You can do all these things in grails. It supports all existing Java classes and spring configurations (grails is built ontop of spring mvc)
However, I really wouldn't recommend moving the whole application to grails. You can perhaps move only the web layer, if you have web developers that are not java experts.
The service layer, the data access, etc, better remain pure Java. That is, only your web controllers - the components that gather the user input, handle http requests and sessions, should use grails. The rest - the stateless service classes and your domain model would better be Java. That's my opinion, but I have already some experience with grails, and static typing in the service layer will save you much trouble.
2) Yes you can use CXF as is. There is a nice layer on top of CXF called GroovyWS. I have only used it for consuming SOAP services, but maybe it has something for REST as well. It's really easy to use.
For consuming REST services I have used HTTP Builder
4) Yes. You can continue to use e.g. spring config for configuring the datasource, or any other way you do it today. Multiple datasources is no problem.
5) I have recently tried using Grails (1.2.1) with Maven. It works, but there has been some issues with both Maven and Grails trying to do dependency management. The documentation is maybe the worst part. I haven't tried upgrading to 1.3 yet because of some major Maven-related JIRAs, but 1.3.2 is right around the corner, and those issues have now been resolved :) There will also be a 1.3.2 maven archetype. Looking forward to that. "Deployment and resolution of plugins from Maven repositories" is one of the new features of Grails 1.3, so things are probably better. Roadmap for 1.3.2 says release today, but there are 8 issues left at time speaking, so my guess would be tomorrow, the Grails releases are usually on time. If you can wait for that, you will probably save yourself some trouble.
If you are looking for rapid application development but aren't otherwise particularly enthused about groovy, you should look into spring-roo. It offers the same kind of RAD functionality, but builds a completely standard java + ORM + spring-mvc app (which has no actual dependencies (runtime or compile) on roo). It's definitely not as mature as grails, but you may find that it better suits your existing experience with statically typed java code and existing ORM, etc. I've only done a couple of small pet projects in roo, but I've been very impressed so far, particularly with how easy it is to customize the generated code and move back and forth between written and generated code. The initial tutorial is very rapid and quite revealing.
I am looking for something very close to an application server with these features:
it should handle a series of threads/daemons, allowing the user to start-stop-reload each one without affecting the others
it should keep libraries separated between different threads/daemons
it should allow to share some libraries
Currently we have some legacy code reinventing the wheel... and not a perflectly round-shaped one at that!
I thought to use Tomcat, but I don't need a web server, except maybe for the simple backoffice user interface (/manager/html).
Any suggestion? Is there a non-web application server, or is there a better alternative to Tomcat (more lightweight, for example, or easier to configure)? Thanks in advance.
Have you looked at OSGi ? You can load/unload bundles (basically .jar files with metadata) independently of each other, and optionally define dependencies between these (with a software lifecycle defined such that bundles are aware of other bundles being loaded/unloaded).
I have found the Jetty "contexts" concept very useful in handling applications (packaged as WAR's and with servlet context listeners), where the xml-file placed in contexts/ describe fully what you want to have started. When you remove the xml-file again, the thing described is stopped.
If you do not start a server connector you will just have a start-stop thing which sounds like what you are looking for.
Jetty can be made very small so the overhead is not bad.
You could consider Spring dmServer. It's a rather non-traditional appserver, with a very lightweight OSGi core (the web container is optional, for example), but it gives you classloader isolation and basic container services. It's not a JavaEE container, but comes with plug-in modules that are.
You're stlll going to have to do a lot of work yourself, but the basics of dmServer are very sound.
No one stops you from sending binary and text data instead of HTML-pages using http protocol. That is whats servlets are for. So I would use the tomcat server.