What is the default scope on actions in struts2? [duplicate] - struts2

My question is not only if action classes can be scoped to singleton, but I also want to know which are the best practices. Both in context of Struts2 and Spring. Best scope of VIEW (say request or session), for controller and model.

Struts2 Actions are managed by the Struts Container. They are ThreadLocal, hence every request has its own thread-safe copy of the Action.
If you use Spring to handle them through the Struts2-Spring-plugin, there are multiple levels of usage:
you can let the Struts container instantiate them, and handle them through Spring for the Dependency Injection, or
you can let Spring take over control and be fully responsible for the whole lifecycle of every Action. In this second case:
if you declare an action as a bean in a Spring XML configuration file, the action will get the default Spring scope, that is Singleton (scope="singleton"). THIS IS DANGEROUS, USELESS, and 99.99% of the times NOT WHAT YOU WANT, because you will lose a fundamental part of the framework capability, actions will be turned into kind-of servlets, thread-UNsafe, and many problems will arise;
to prevent that, you can put the scope="prototype" in the bean declaration, that will let Spring instantiate the action without affecting its nature.
If you are inside a container Java EE 6+ compliant (for example, Jboss 7, Wildfly 8, TomEE 1.7, Glassfish 3+, ecc...), the Contexts and the Dependency Injections are handled through CDI. If you want, you can use the Struts2-CDI-plugin to allow CDI to handle your actions and inject dependencies through the #Inject annotation (instead of the #Autowired one)
I've used Spring a lot in the past, then after discovering CDI and the CDI plugin, I've switched and never looked back, so I vote for the n.3

Related

Why do you use DelegatingFilterProxy in springSecurity and what are the benefits of this design?

What I don't understand is why this security framework USES proxy classes to invoke filters. What are the benefits of this design?
I think the documentation of DelegatingFilterProxy gives you quite pretty explanation:
[...] All
calls to the filter proxy will then be delegated to that bean in the
Spring context, which is required to implement the standard Servlet
Filter interface.
This approach is particularly useful for Filter implementation with
complex setup needs, allowing to apply the full Spring bean definition
machinery to Filter instances. Alternatively, consider standard Filter
setup in combination with looking up service beans from the Spring
root application context.
NOTE: The lifecycle methods defined by the Servlet Filter interface
will by default not be delegated to the target bean, relying on the
Spring application context to manage the lifecycle of that bean.
Specifying the "targetFilterLifecycle" filter init-param as "true"
will enforce invocation of the Filter.init and Filter.destroy
lifecycle methods on the target bean, letting the servlet container
manage the filter lifecycle. [...]

Can session scope beans be used with Spring Session and GemFire?

Can "session" scope beans be used with Spring Session and Pivotal GemFire?
When using Spring Session for "session" scope beans, Spring creates an extra HttpSession for this bean. Is this an existing issue?
What is the solution for this?
Regarding...
Can session scoped beans be used with Spring Session and GemFire?
Yes!
In fact, it does not matter which underlying "provider" is used with Spring Session either. For example, either Spring Session with GemFire/Geode (docs) or Spring Session with Redis (docs), etc, can be used and it will work just the same (in the same way).
As for...
If using Spring Session for session scoped beans Spring creates extra HttpSession for this bean, is this an existing issue?
Well, this is not exactly true.
You have to understand the underlying technologies in play here and how they all work together, including Spring Session, the Spring Framework, the Servlet Framework, your Web container (e.g. Tomcat), which is bound by the contract specified in the Java EE Servlet spec, and any other technologies you may have applied (e.g. Spring Security's Web support).
If we dive deep into Spring's architecture/infrastructure, you will begin to understand how it works, why it works and why your particular statement ("Spring creates an extra HttpSession for this bean") is not correct.
First, Spring Session registers an all important Servlet Filter, the o.s.session.web.http.SessionRepositoryFilter.
There are many different ways to do this, and the Javadoc for javax.servlet.Filter essentially hints that this is done via the Web Application "deployment descriptor".
Of course, given our menagerie of configuration options today, a Web Application deployment descriptor is pretty loosely defined, but we commonly know this to mean web.xml. However, that is not the only way in which we can configure, essentially, the Web Application's ServletContext.
Spring supports both web.xml based deployment descriptors as well as JavaConfig using the Servlet (3.0+) API.
In web.xml you would register (for example) the Spring Frameworks' o.s.web.filter.DelegatingFilterProxy, that delegates to an actual javax.servlet.Filter implementation (when Spring Session is in play, that would be the o.s.session.web.http.SessionRepositoryFilter, of course) which is also declared/defined as a "bean" (first this, then this) in the Spring container. This is necessary in order to auto-wire (inject) the appropriate Spring Session o.s.session.SessionRepository implementation (also a Spring managed bean defined in the container, e.g. for Redis) that knows how to delegate (HTTP) Session state management to the underlying "provider".
In the JavaConfig approach, the registration is performed via the core Spring Framework's o.s.web.WebApplicationInitializer concept. Read the Javadoc for more details.
Well, Spring Session provides such a WebApplicationInitializer to initialize (HTTP) Session management, the o.s.session.web.context.AbstractHttpSessionApplicationInitializer. Typically, when using Spring's Java-based Container Configuration and/or Annotation configuration approach, a developer would create a class that extends this Spring Session provided class and register the necessary configuration (e.g. connection criteria) for the underlying Session management provider; for example (see also this). The Config class is annotated with #EnableRedisHttpSession which imports the Spring #Configuration class that declares/defines the appropriate Spring Session SessionRepository implementation for the "provider" (e.g. again Redis), which is needed by the Servlet Filter (again SessionRepositoryFilter).
If you look at what the Spring Session AbstractHttpSessionApplicationInitializer does, you will see that it registers the Spring Session, SessionRepositoryFilter, indirectly via Spring Framework's DelegatingFilterProxy... from insert, then here, then here and finally, here.
As you can see, the Spring Session SessionRepositoryFilter is positioned first in the chain of Servlet Filters. The !insertBeforeOtherFilters is negated since the parameter in javax.servlet.FilterRegistration.Dynamic.addMappingForUrlPatterns(dispatcherTypes, isMatchAfter, urlPatterns...) is "isMatchAfter".
This is essential, since the Spring Session's o.s.session.web.http.SessionRepositoryFilter replaces both of the javax.servlet.http.HttpServletRequest and javax.servlet.http.HttpServletResponse. Specifically, by replacing the javax.servlet.http.HttpServletRequest, Spring Session can provide an implementation of javax.servlet.http.HttpSession (when HttpServletRequest.getSession(..) is called) that is backed by Spring Session and the provider of the developer's choice (e.g. Redis, GemFire), the whole purpose of Spring Session in the first place.
So, the Servlet Filters see the HTTP request/response before any framework code (e.g. Spring Framework's session scoped bean infrastructure), and especially before any of the Web Application's Controllers or Servlets, get to see the HTTP request/response.
So, when the core Spring Framework's session scoped bean infrastructure sees the (HTTP) Servlet request/response, it sees what Spring Session handed it, which is just an implementation the regular javax.servlet interfaces (e.g. HttpSession) backed by Spring Session.
Looking at the core Spring Framework's o.s.web.context.request.SessionScope "custom" implementation (which handles bean references/bean lifecycles for session scoped beans declared/defined in the Spring container), which extends o.s.web.context.request.AbstractRequestAttributesScope, you see that it just delegates to the o.s.web.context.request.SessionRequestAttributes class. This class is created primarily by Spring's DispatcherServlet, and defines all of its operations (e.g. setAttribute(name, value, scope)) in terms of the "provided" scope defined by the bean (definition) in question. See the source for more details. So the bean gets added to the appropriate HTTP session.
Sure, Spring "will" create a new javax.servlet.http.HttpSession on the first HTTP request, but not without Spring Session's infrastructure knowing about it, since what Spring is using in this case is an implementation of javax.servlet.http.HttpSession backed by Spring Session's "Session".
Also, getSession(true) is also just an indication that the HttpSession is "allowed" to be created if it does not already exist! A Servlet container simply does not keep creating new HTTP sessions for every HTTP request, so long as the session ID can be determined from the HTTP request (which is done via either URL injection... jsessionid or with a cookie, typically). See the javax.servlet.HttpServletRequest.getSession(boolean) for more details.
Anyway, the only other caveat to this entire story is, you need to make sure, especially for GemFire, that...
The Spring "session" scoped beans defined in the container are serializable, either using Java Serialization, or 1 of GemFire's serialization strategies. This includes whatever the bean references (other beans, object types, etc) unless those "references" are declared transient. NOTE: I am not entirely certain GemFire Reflection-based PDX serialization approach is entirely "aware" of "transient" fields. Be conscious of this.
You must make certain that the classes serialized in the session are on the GemFire Servers classpath.
I am working on a configuration option for Spring Session Data Geode/GemFire at the moment to support PDX, but that is not available yet.
Anyway, I hope this helps clear up the muddy waters a bit. I know it is a lot to digest, but it all should work as the user expects.
I will also add that I have not tested this either. However, after reviewing the code, I am pretty certain this should work.
I have made it a task to add tests and samples to cover this situation in the near future.
Cheers!
-John

Using the Grails Cache Plugin Annotation on Normal Groovy Classes

Is it possible to use the Grails Cache plugin's annotations (ie: #Cacheable) on methods in normal Groovy classes? The plugin's documentation doesn't mention anything about normal Groovy classes and based on my own tests the annotations have no effect when used in a normal class. So I'm just wondering if there's a way to get the annotations to work in a normal Groovy class.
The current alternative is to simply directly access the cache in the method via the Cache Manager bean, but it would be nice to use the annotations instead.
No, the annotation only works on services and controllers. The plugin detects the annotation and creates a proxy for the service which intercepts all method calls and does the cache-related work first. So if there is a value in the cache for that method, it won't bother calling your real method but return the cached value instead. But if it's not cached, it will call your method and use its return value, but cache that for later.
This works because you have to retrieve the service from the Spring ApplicationContext (or have Grails do that for you) and this gives Spring a chance to give you the proxy instead of the real implementation instance, but there's no way for Spring to know about access to regular Groovy classes without AOP or some other more invasive solution.
Having said that, the plugin is probably being overly strict in limiting to only controllers and services. It handles controllers specially because those involve caching web requests instead of method return values, but there shouldn't be much difference between a Grails service and any other annotated Spring bean as far as caching goes. You can add your own Spring beans, either manually in grails-app/conf/spring/resources.groovy or by adding them to the grails.spring.bean.packages list in Config.groovy, so the plugin should be updated to look for all annotated classes. You can request this in the plugin's JIRA at https://jira.grails.org/browse/GPCACHE

Struts2 + Spring, is the Spring Plugin required?

I'm replacing the service tier in an existing older Struts2 project with Spring service beans developed for another project.
I'd like to just #Inject these service beans into my Action classes.
Is it required to use Struts' Spring Plugin? Or can I add Spring into my Struts web application like I would any other (ContextLoaderListener, applicationContext.xml, context:component-scan)?
Am I missing some reason why the Struts Spring plugin helps me in another way?
Many thanks!
Well you can do the most of the things what you have described in your question as Services layer is completely out of view for the S2 and Struts2 do not care how you are creating your Service layer instances and other things.
Benefits i am seeing of using Struts2-Spring plugin is to delegate creation of Struts2 related things to Spring like Action classes creation,Interceptors,Results etc.
My Suggestion is to use the plugin as you are going to use the Spring in your application so its very good and flexible as well powerful to use the power of Spring DI to create required objects needed by S2 else S2 will use its own data creation factory to create framework component.
Why wouldn't you use the Spring plugin?
It's essentially invisible, uses Spring to create your actions (including injecting other Spring beans), etc.
Guice's #Inject doesn't know anything about Spring beans, AFAIK, so you'd be naming classes manually, they'd be instantiated via normal Java/Guice mechanisms, wouldn't be injected with their own Spring dependencies (unless you did it manually, or via AOP, or whatever).
You'd also need to use non-Spring mechanisms for doing injection in testing, which is fine, but unless you provide more details regarding your usecase, I don't really see a reason to bypass the functionality the Spring plugin provides out-of-the-box.

Business logic in JSF based app

Where should I put the logic of my app when i'm using JSF framework? As I understand managed beans are used only for getting/setting the properties of the form and also have controllers methods. I don't think that implementing the logic in controllers method is a good way. Of course I can use ejb to implement the logic and inject it to managed beans, but how it will work on servers that don't have an ejb container(e.g. Tomcat).
I don't think that implementing the logic in controllers method is a good way.
Indeed. Use business services like EJBs.
Of course I can use ejb to implement the logic and inject it to managed beans, but how it will work on servers that don't have an ejb container(e.g. Tomcat).
You could use OpenEJB to enrich it with (limited) EJB 3.x capabilities. An alternative is Spring, that's what they used during the EJB 2.x era when EJBs were hated.

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