I have a Spring boot project with many beans, so I can't just use my IDE to look understand the beans dependency tree.
So given a lazy bean method, how can I see why it was initialized? I mean what other Spring bean was dependent on it and resulted in its initialization?
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I’m taking this udemy course all about Spring Hibernate etc. The course started with explaining how Injection of Control and dependency injection works not in a web perspective just like having simple classes or beans, defining beans and their dependencies inside a config xml file or inside the actual class Using java annotation and then a main class where the beans are created. I understood that despite not really seeing the big benefit of using IoC and DI other than separating roles like creating and maintaining objects and adding dependencies the object needs and I guess when the project is bigger this makes it cleaner and easier to follow right?
However what I don’t understand is how IOC and DI ties in a full spring MVC project. Like I understand using the #Controller annotation means it’s like an #Component and you could make it scan the components automatically when it creates beans but like unlike before there isn’t a main class where beans are created and configured rather I have a controller class where I manually create objects and models and pass that back to the views where I can use the values in the model. I don’t see how I use IoC or DI here? Or is it because it’s a simple project and perhaps the objects we created didn’t have many dependencies?Or are a lot of the uses and implementation done internally or automatically?
I am just struggling to a) see why IoC and DI are that important and b) how are they actually used in a Spring MVC project where you don’t have a main class where you do create beans.
A) Create a project, but don't add any dependency (or web-mvc). Then do it yourself then see how much need time to create configure manually. If it is just a simple mvc project, you can do it manually, but if your project increase day by day then a huge configuration file to maintain your project properly. But when you are professional developer, you don't have so much time to configure all those manually. So here is come the solution IoC and DI. Controller or other anotation are configured in build-in jars. You don't have to worried about to create controller or to create bean, just use them when you neer them. It's save your time as well as headache about is it working or not. It's increase your productivity while your are working on a big project.
B) Yes, there is no main class in web project. To run a web project, you need a server. The server first looking for a configuration (In spring, it's web.xml, dispatcher-servlet). If it available then expand the configuration file, if not then throw an error. In that configuration file, explain everything about the web project. What should do, what is not mandatory, what is entry point etc.
So, IoC and DI are very important because to understand how a web project work behind the scene or how all component work together.
IoC is a process whereby objects define their dependencies, that is, the other objects they work with, only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method. The container then injects those dependencies when it creates the bean. This process is fundamentally the inverse, hence the name Inversion of Control (IoC), of the bean itself controlling the instantiation or location of its dependencies by using direct construction of classes, or a mechanism such as the Service Locator pattern.
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.
The advantages of this architecture are:
decoupling the execution of a task from its implementation
making it easier to switch between different implementations
greater modularity of a program
greater ease in testing a program by isolating a component or mocking its dependencies and allowing components to communicate through contracts
Inversion of Control can be achieved through various mechanisms such as: Strategy design pattern, Service Locator pattern, Factory pattern, and Dependency Injection (DI).
You can go with Annotation based configuration, where you can define #Configuration class and return the required beans using #Bean annotation.
Also you can use #Component to your POJO class to treat it as Spring bean.
I am coming at this question from many years of using spring and just starting to look at JEE7 and CDI.
In the Spring world you have to stick #Component on a bean to turn into spring bean that spring will inject with dependencies but in CDI it seems that there is no equivalent of #Component.
To me CDI seems to imply that every class in my web application will be considered a CDI bean which seems undesirable because I have lot of java classes that are not using injection and I would not want some one to just stick #Inject in those classes and have CDI do its magic.
Two questions:
How to restrict what CDI considers to be a managed bean in a jar file?
What is the benefit for CDI to consider every bean to be a managed bean?
Please see the documentation for bean-discovery-mode in beans.xml. This attribute was only made available in JEE7 and is not available in JEE6.
How many BeanFactories can a spring application can have? I got this doubt when i see the source code of a spring based web application where they used an xml based configuration for a set of beans as well as annotation based configuration for the rest. Is this produce multiple bean factories or single at startup?
Definitely need more information on config to tell for sure.
The easiest way to find out is by using their visibility. Try to inject beans declared in the xml configuration in one of the beans using annotations, if it works they are using the same bean factory -
The probabilities are that it is the case. It is not unusual to have a mix of bean and annotation based configuration. Some people prefer to move configuration which they know for sure will not require to the flexibility of switching in a config file into beans. This reduces a lot of clutter in the xml configuration.
we recently converted our project from JBoss seam to using Spring and JSF. Our controller needs to initialize some properties. Right now were simply using the constructor to call the initialization methods. Seam has #Factory annotation decorated to a method which is called whenever the accessed property/field is null. Does Spring have an equivalent annotation? Thanks a lot.
No, but Spring supports the JSR-250 lifecycle annotations #PostConstruct / #PreDestroy, which you can use for housekeeping when your bean starts up.
In fact there are at least three mechanisms for bean lifecycle management, and their interaction and precedence is explained in the chapter "Combining lifecycle mechanisms"
What is a bean in spring framework?
What is the use of the bean?
In the context of Spring, a bean is a managed object. What is a managed object? It's an object that Spring is aware of and that Spring knows how to manipulate, e.g. inject properties, invoke callback methods, etc.
There is then a difference between a regular java class (which Spring doesn't know about) and beans (which Spring knows about).
Generally Spring beans follow the Java bean convention, so that Spring can manipulate them easily. For instance if the bean is declared to have a property xxx, then Spring will expect getXxx and setXxx to be present. However, since Spring 2.X it is possible to dependency-inject private variables (using annotations), and therefore it is is no longer necessary to define a public setter in order to enable dependency injection for a property.
( The term bean is confusing in the sense that it is frequently uses to denote either (1) something that is managed by a container, like an enterprise java bean (EJB) or (2) something that adheres to the Java bean conventions. )
The Java Bean spec does spell out no-arg constructor, getters/setters, and serializable, but Spring does not require that your beans follow the spec. Spring deals with Plain Old Java Objects, whether they conform to the Java Bean spec or not.
What's the use of beans? They express your wishes in code. All Spring is doing is managing their lifecycle and wiring them together to accomplish your goals.
a bean is a POJO with setters and getters that follow the bean convention.
beans are used to pass around data, also jsps has special support for beans
A bean in Spring world is any object that is defined using Spring conventions using bean id or name. Its life time is managed by Spring container. The bean can be a POJO or a factory instance with static methods. It can even be a JNDI resource and not necessary a Java Bean. Bean managed by the Spring container can even be a proxy bean which may hide the bean (esp with TransactionProxyFactory).
In short, any bean whose lifetime is managed by Spring container is a Spring bean.
a bean is a class with a public standard constructor, getters/setters (properties) and it must be serializable. wikipedia has an explenation on this.
this way the spring framework knows how to create an instance of the bean (public standard constructor) and which properties exist (with reflection)