@Autowired(required = false) in Spring Bean

In this article, we will discuss the the importance of required = false attribute in @Autowired ie., @Autowired(required = false).

@Autowired annotation is used to inject dependency beans into a bean. You can also read @Autowired vs @Inject vs @Resource for more details.

The default value of the required attribute is true. So, when required = true, the injection of the dependency bean is mandatory. So in the absence of any auto-wiring candidate , the auto-wiring will fail and Spring will throw an exception.

In the below example, if there is no auto-wiring candidate or qualifying bean for Class1, then Spring will throw an example.

package com.spring.beans;

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

@Component
public class Class2 {

    @Autowired //required=true by default
    private Class1 Class1;

    public Class1 getClass1() {
        return Class1;
    }

    public void setClass1(Class1 class1) {
        Class1 = class1;
    }

}

Field Class1 in com.spring.beans.Class2 required a bean of type 'com.spring.beans.Class1' that could not be found.

The injection point has the following annotations:
	- @org.springframework.beans.factory.annotation.Autowired(required=true)


Action:

Consider defining a bean of type 'com.spring.beans.Class1' in your configuration.

So, in case you are not sure about the availability of auto-wiring for the dependency or if the dependency is not mandatory, then you can specify @Autowired(required=false).

Setting the required attribute to false indicates that the property is not required for autowiring purposes, and the property is ignored if it cannot be autowired.

Let’s build a small Java project for our use case.

Technology Stack

• Spring Boot
• Spring Core
• Core Java

Project Structure

Code

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>SpringAutoWire</groupId>
	<artifactId>SpringAutoWire</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.1.RELEASE</version>
		<relativePath />
	</parent>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>
</project>

package com.spring.beans;

public class Class1 {


}

package com.spring.beans;

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

@Component
public class Class2 {

    @Autowired(required = false) //Specfied required=false explicitly
    private Class1 Class1;

    public Class1 getClass1() {
        return Class1;
    }

    public void setClass1(Class1 class1) {
        Class1 = class1;
    }

}

package com.spring.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

import com.spring.beans.Class2;

@SpringBootApplication(scanBasePackages = "com.spring.beans")
public class Application implements CommandLineRunner {

    @Autowired
    private ApplicationContext context;

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }


    @Override
    public void run(String...args) throws Exception {
        Class2 class2 = context.getBean(Class2.class);
        System.out.println("Class1:" + class2.getClass1());
        System.exit(1);
    }

}

Class1:null

Download Code

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