Java based bean configuration

Introduction

In Java, a Spring Bean is an object that is created and managed by Spring IoC container. In Java-based configuration, Beans can be defined using @Configuration and @Bean annotations. There are multiple ways to define and configure beans, as briefly overviewed in Loose Coupling in Spring Boot - PART 2 including XML-based, Annotation-based, and Java-based configurations. In this article, we'll delve into Java-based configuration.

Steps for Configuring Spring Beans

Create classes (Components) that'll be managed as Beans by Spring IoC container. Here, we'll create three java classes namely MyController, MyService, and MyRepository whose objects should be managed using Spring Beans.

 package com.mypackage.controller;
 import com.mypackage.service.MyService;

 public class MyController {
     //Controller -> Service Layer -> Data Layer(Repository)
     private final MyService myService;

     public MyController(MyService myService) {
         this.myService = myService;
     }

     public String handleRequest() {
         return myService.serveRequest();
     }
 }

 package com.mypackage.service;

 public class MyService {
     public String serveRequest() {
         return "Service Layer";
     }
 }

 package com.mypackage.repository;

 public class MyRepository {

     public String getData() {
         return "Data Layer";
     }
 }

Create a Java class and annotate it with "@Configuration". This class will contain methods annotated with "@Bean" to define your Beans.

 package com.mypackage.config;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;

 @Configuration
 public class AppConfig {

     @Bean
     public MyService myService() {
         return new MyService();
     }

     @Bean
     public MyRepository myRepository() {
         return new MyRepository();
     }

     /*Creating Bean (name = myController, type = MyController) using 
     existing Bean (name = myService, type = MyService)*/
     @Bean
     public MyController myController() {
         return new MyController(myService());
     }
 }

Ensure that Main application class does the task of launching context.

 package com.mypackage;

 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import com.mypackage.repository.MyRepository;
 import com.mypackage.config.AppConfig;
 import com.mypackage.controller.MyController;

 public class MyApplication {

     public static void main(String[] args) {
         //Launch Context with configurtion AppConfig.java
         var context = new AnnotationConfigApplicationContext(AppConfig.class);
         //Get Bean by Type
         MyController myController = context.getBean(MyController.class);
         MyRepository myRepository = context.getBean(MyRepository.class);
         //Call a method on Bean
         System.out.println(myController.handleRequest());
         System.out.println(myRepository.getData());        
     }
 }

Output

Service Layer
Data Layer

Summary

In this article, we explore how to configure Spring Beans using Java-based configuration, detailing steps from creating classes to defining them as Beans with @Configuration and @Bean annotations. Using a simple example with a controller, service, and repository, we demonstrate how to set up, manage, and retrieve these Beans within a Spring Boot application.

Java Beans Demystified: A Guide to Java-Based Configuration

Table of contents

Introduction

Steps for Configuring Spring Beans

Output

Summary