An example is if my spring controller has two Autowired services, and both services have a PersistenceContext also controled by spring (and i'm doing nothing more), will both share the same context in every request by default?
No, they will use different ones. A persistence context (EntityManager) is defined to be a thread-bound concept in JPA. Thus each request will see a fresh instance of EntityManager for each new request.
For a singleton Spring component that gets an EntityManager injected, Spring will autowire you a proxy instance so that it can easily exchange the backing instance. This a core Spring container feature and doesn't need anything in Spring Data JPA (see the documentation here).
Related
I am coming from the .NetCore Background and learning Hibernate now for a new Project.
Previously I have worked with Entity Framework Core (EF Core) and Hibernate looks quite similar too.
I have some questions though:
In .NetCore, one could mark make EF Core DbContext either as a Transient (Prototype in Spring) or Scoped (Request in Spring).
What is the default Bean Scope for the Hibernate Session or Persistence Context? and how do I change it to Request Scope?
I was working on a Spring-data-jpa project with spring boot, I see that the creation of repository beans required a datasoure bean to be present, Why is it so?
And can a repository bean be created without datasource bean.
The purpose of a repository is to load and save data into a persistent store.
Spring Data JPA does that using JPA so it needs an EntityManager which in turn need a DataSource.
Strictly speaking the DataSource is only used once the database is actually accessed.
While you definitely nee a DataSource bean you may delay the construction of a normal DataSource by providing a wrapper which instantiates the the actual DataSource at a later point in time.
DelegatingDataSource might be of help, either as a basis class or, since you are going to change the DataSource as a template for an implementation.
See the somewhat related question https://stackoverflow.com/a/61208585/66686
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'm new to Spring and a little confused about how it works. I get that I can use the application context to instantiate beans and have them populated. However, is the idea that I should be able to just write Bean b = new Bean() and then have Spring to somehow automagically populate that Bean?
I'm experimenting with Spring in a web application, and as far as I can see I need to inject the ApplicationContext into, say, the servlets to be able to instantiate other beans (services, daos etc.) from there. It's a bit cumbersome, but probably works.
However, is Spring meant to be able to hook into any object instantiation which happens on classes defined as beans in applicationContext.xml?
Spring is an Inversion of Control container. A bean is an object whose life cycle is managed by Spring. If you want Spring to populate an object, it needs to go through Spring, ie. it needs to be bean.
is Spring meant to be able to hook into any object instantiation
which happens on classes defined as beans in applicationContext.xml?
Spring doesn't hook into anything. You configure your beans and the relationships between them with Spring and Spring handles creating the instances and linking them up.
For domain objects, Spring provides a solution via the #Configurable annotation: http://docs.spring.io/spring/docs/4.0.0.RELEASE/spring-framework-reference/htmlsingle/#aop-atconfigurable
It requires compile- or load-time-weaving and, thus, introduces some additional complexity but having the convenience of using the standard new Bean() syntax plus Spring's autowiring is worth it in my opinion.
Alternatively, you could define your domain objects as beans with prototype scope and use some factory to create them using the Spring ApplicationContext.getBean() method. With a scope of prototype a new instance will be returned every time and since you go through the ApplicationContext, Spring will do all the dependency injection magic as usual.
As for services and other beans with singleton scope, you would typically NOT retrieve them by first injecting the ApplicationContext and using it but instead you would inject them via either a constructor, setter or annotation-based strategy. The documentation covers that in detail: http://docs.spring.io/spring/docs/4.0.0.RELEASE/spring-framework-reference/htmlsingle/#beans-factory-collaborators
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