Understanding Spring's @Required Annotation: A Legacy Perspective

While the @Required annotation has been deprecated since Spring Framework 5, it's not uncommon to encounter it in legacy projects.

So, why should you care?

Not every project is built on a fresh new Spring Framework version; there are a lot of legacy projects out there, and maybe you are working on one right now or will work on one in the future.

So, after reading this blog post, you will understand what this annotation does and how it's used.

Maybe you are reading this right now because of it.

What @Required Does

It tells Spring that a specific bean property, as the annotation name says, is required.

It is a method-level annotation that checks if the required property was set at configuration time. If the dependency is not provided when the bean was created, Spring will throw a BeanInitializationException.

This was useful in the past to make some bean properties mandatory.

Today, you can achieve this by putting the dependencies in the bean constructor or by using an @Autowired annotation in the set method.

How Was It Used?

Assuming we have this bean definition:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans> http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="employee" class="Employee">
        <property name="name" value="John Doe" />
    </bean>
</beans>`

And this Java code:

public class Employee {
    private String name;

    @Required
    public void setName(String name) {
        this.name = name;
    }
}

The @Required checks if the name property was set. If it is not, it will throw the exception we mentioned above, when trying to configure this bean.

Now the next time you work on a legacy project, you’ll be already familiar with this annotation.

If you like this topic, make sure to follow me, in the following days, I’ll be explaining more about the Spring annotations!

Stay tuned!

Willian Moya (@WillianFMoya) / X (twitter.com)

Willian Ferreira Moya | LinkedIn

References

• https://www.tutorialspoint.com/spring/spring_required_annotation.htm
• https://www.geeksforgeeks.org/spring-required-annotation-with-example/
• https://docs.spring.io/spring-framework/docs/2.5.6/javadoc-api/org/springframework/beans/factory/annotation/Required.html