How to Autowire in Java Spring Boot

1. Used Modes for @Autowired Annotation
2. Utilize @Autowired in Java Spring Boot

Spring Boot is a popular framework of Java. In Spring Boot, the most commonly used annotation is @Autowired, mainly used to automatically collect the bean.

In this article, we will discuss the @Autowired in Java Spring Boot.

Used Modes for @Autowired Annotation

The following are the commonly used modes for the @Autowired annotation.

Utilize @Autowired in Java Spring Boot

First, we will create a class named ClassB which we want to autowired from the parent class. The code example for this class will be like the following.

package com.sample.demo;
import org.springframework.stereotype.Component;

@Component
public class ClassB {
  void showMSG() {
    System.out.print("This is autowired !!!");
  }
}

This child class contains the method named showMSG(), and we declared it as a bean component using the annotation @Componant. Now we are going to look at its parent class.

Below is the code for our parent class.

package com.sample.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class ClassA {
  @Autowired ClassB b;

  void getMSG() {
    b.showMSG();
  }
}

In our parent class, we autowired the ClassB and this class contains a method named getMSG(). We declared this class as a bean component using the annotation @Componant.

Now let’s take a look at our handler class.

package com.sample.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class DemoApplication {
  public static void main(String[] args) {
    ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    ClassA a = context.getBean(ClassA.class);
    a.getMSG();
  }
}

Here, we get the bean of ClassA from the context. After that, we called the method getMSG() from the bean.

Output:

This is autowired

Please note that the code snippets shared in this article are written in the Java Spring Boot framework. You must install the necessary plugins for your IDE before executing this program.