Contexts and Dependency Injection Framework

Contexts and Dependency Injection (CDI) is an interface that standardizes dependency injection for Java EE. It defines different annotations for dependency injection like @Named, @Inject, @Scope, @Singleton, etc. Different CDI implementation frameworks provide support and functionality for these annotations.

@Named is used to define a bean and @Inject is used for autowiring one bean into another. Spring supports most of the annotations defined by CDI.

For the code example shown in this lesson, we have created a sub-package called lesson12 inside the package io.datajek.spring.basics.movierecommendersystem. The package contains MovieRecommenderSystemApplication.java, Filter.java, ContentBasedFilter.java, CollaborativeFilter.java, and RecommenderImplementation.java files. To be able to use CDI annotations in our Spring application, we need to add a dependency in the pom.xml file as follows:

<dependency>
    <groupId>javax.inject</groupId>
    <artifactId>javax.inject</artifactId>
    <version>1</version>
</dependency>

The dependency is automatically downloaded when the pom.xml file is saved and is visible in the Maven Dependencies folder as javax.inject-1.jar. This jar lists the annotations defined by CDI. Now, we can use these annotations in our application.

@Named

Spring framework provides an implementation for some CDI annotations. In Spring framework, a bean is declared using the @Component annotation. However, it also supports the @Named annotation. This means we can replace the @Component from the RecommenderImplementation, ContentBasedFilter, and CollaborativeFilter classes and use @Named to declare components.

Let’s have a look at the annotation replacement in the RecommenderImplementation class first: