Resolve Dependency Injection Conflicts in Production | Spring | Spring boot | Java

If one service depends on another service to work, then the object of that dependent service is injected at runtime by Spring IOC Container. That is Dependency Injection.

In the real world applications we will not have dependency injection as simple as given in most of the online tutorials.

We'll have multiple implementations of same service. Spring will not be able to decide which implementation to Inject. This problem is known as Dependency Injection Conflict.

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0:00 Dependency Injection
0:34 Dependency Injection Conflict
1:16 Dev: Controller
2:30 Dev: Service
4:03 Story so far
4:57 Testing Application
5:32 Adding Conflict for Dependency Injection
6:07 Analyzing Logs to identify Issue
8:08 @Primary Annotation
9:28 @Qualifier Annotation
11:07 byName Strategy

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The Spring Framework is an application framework and inversion of control container for the Java platform. The framework's core features can be used by any Java application, but there are extensions for building web applications on top of the Java EE platform.(Wikipedia)

A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds Bean Definitions of multiple beans within itself and then instantiates the bean whenever asked for by clients.

The BeanFactory is the actual container which instantiates, configures, and manages a number of beans. These beans typically collaborate with one another, and thus have dependencies between themselves. These dependencies are reflected in the configuration data used by the BeanFactory

BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.

Bean life cycle is managed by the spring container. When we run the program then, first of all, the spring container gets started. After that, the container creates the instance of a bean as per the request, and then dependencies are injected. And finally, the bean is destroyed when the spring container is closed. Therefore, if we want to execute some code on the bean instantiation and just after closing the spring container, then we can write that code inside the custom init() method and the destroy() method.

Spring Bean Scope in a nutshell refers to the lifecycle and visibility of a bean instance in a Spring-based application. Bean scopes determine the number of instances of a bean that will be created and how long the bean instances will exist. The five main scopes in Spring are: Singleton, Prototype, Request, Session, and Global Session.

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