I can't find this information anywhere.
Can someone explain how spring boot 'decides' what the right scope is?
Are the beans all singletons?
Spring Boot doesn't decide anything about the bean scope, this is plain Spring framework functionality. Default bean scope is singleton scope (meaning, one instance of that bean in the application).
Here is the official documentation:
https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/core.html#beans-factory-scopes
Default scope for a Spring Bean in singleton.
Related
I am having a JSF application and I am using Spring for bean management. I registered all JSF beans as Spring beans and everything was running very smoothly. Now, I have got a requirement to use JSF's view scope, so it means I have to create a JSF managed bean (which I did using JSF annotations and all).
Now, I want to access this JSF bean in a Spring bean, certainly I cannot inject or get it using Spring's application context because Spring container doesn't know about this bean. So, currently in my Spring bean code I am getting this JSF bean using JSF's EL Resolver (examples mentioned here).
What I want to know is that is there any better way to do this?
My application is on Spring 4.0 and JSF 2.0 (MyFaces implementation), please let me know if you need any other information. I have not placed code because all my code is in remote server, moreover I think code is not required for this as there is no debugging over here.
I had been reading up on Spring framework documentation and came across this line.
As a rule, use the prototype scope for all stateful beans and the singleton scope for stateless beans.
Couldn't quiet digest it. Isn't the line above counter intuitive and just wrong?
I could accept Stateful EJBs as Prototypal beans which makes sense but wouldn't it run against the very grain or idea of a Stateless EJB to declare it as a singleton bean?
Spring bean scope and EJB -- Read Section 5.5.2 - The Prototype Scope
I'm new to Spring and I'm confused about something basic. Are the classes that are stereotyped (Service, Controller, Repository) treated as beans? I'm confused as to when you actually need to annotate/configure something as a bean and when you don't. Is it for the classes that aren't stereotyped?
Thanks!
From spring documentation:
In Spring, the objects that form the backbone of your application and
that are managed by the Spring IoC container are called beans. A bean
is an object that is instantiated, assembled, and otherwise managed by
a Spring IoC container. Otherwise, a bean is simply one of many
objects in your application. Beans, and the dependencies among them,
are reflected in the configuration metadata used by a container.
Service, Controller, Repository are managed by the Spring IoC container, so they are called beans. You annotate a class as #Serivice, #Controller, #Repository, or more in general #Component when you want spring to manage it: spring will manage the instance of annotated class in regard of the scope you select (not all these scope are always available):
singleton – Return a single bean instance per Spring IoC container
prototype – Return a new bean instance each time when requested
request – Return a single bean instance per HTTP request
session – Return a single bean instance per HTTP session
globalSession – Return a single bean instance per global HTTP
session
I have a Spring bean with scope session. This bean holds a reference to another singleton bean which is not serializable. What is the best approach if I want to serialize the session scoped bean?
The same question is already asked here: Spring session-scoped beans (controllers) and references to services, in terms of serialization
The accepted answer is that:
[...]this issue is resolved in spring 3.0 by providing a proxy of non-serializable beans, which obtains an instance from the current application context
As far as I understand the speaker in the linked video it should "just work". But in my case it doesn't! When I try to serialize my session scoped bean i get a NotSerializableException.
How can I solve this problem?
You need to instruct Spring to create that proxy. In XML-based config, via <aop:scoped-proxy/> tag, in component-scan mode via annotation:
#Scope(proxyMode = ScopedProxyMode.INTERFACES)
on your controller class.
You may mark singleton reference field as transient. Then check How to execute method after deserialization and load reference from ApplicationContext.
Also, please provide stacktrace.
P.S.
It is not too good idea to use session passivation.
I am reading spring through its official documentation and at one place I came to a line that uses prototype scope for all stateful beans while singleton for stateless beans.
I know there is something as stateful as well as stateless beans in EJB but this is not what they have mentioned in the documents.
Can anyone explain to me what exactly this means of stateful as well stateless beans in Spring
Thanks in advance
From spring perspective
stateless beans: beans that are singleton and are initialized only once. The only state they have is a shared state. These beans are created while the ApplicationContext is being initialized. The SAME bean instance will be returned/injected during the lifetime of this ApplicationContext.
stateful beans: beans that can carry state (instance variables). These are created EVERY time an object is required (like using the "new" operator in java).
These are not EJB statfull/stateless session beans.
There is no point in storing specific information like client data, per request data in Singleton bean as they are created only once by Spring IOC container. That's why singleton beans are stateless. They are shared resources. They can only be used for storing global information.
When a request is made for creating a prototype bean, a new request is created every time. So, they can be used to store some specific information for each request. So they are stateful.
It totally depends on the implementation. See tomee for example http://tomee.apache.org/statelesscontainer-config.html . You'll have to check in your server docs