What is the difference between @Inject and @Autowired in Spring Framework? Which one to use under what condition?

Question

I am going through some blogs on SpringSource and in one of the blogs, the author is using @Inject and I suppose he can also use @Autowired.

Here is the piece of code:

@Inject private CustomerOrderService customerOrderService;

So what is the difference between using @Inject and @Autowired and would appreciate it if someone explained their difference and which one to use under what situation.

Sanskrit

I don't have an answer, since I'm new to this too, but this might help sakaenakajima.wordpress.com/2010/08/10/… – Dexter

The difference between '@Inject' and '@Autowired' is explained well in this article alextheedom.wordpress.com/2016/02/13/… – Camisole

Please have a look at this link: concretepage.com/spring/… This feature is supported in @Inject automatically without any (required=false) attribute – Inkwell

Answer 1

Assuming here you're referring to the javax.inject.Inject annotation. @Inject is part of the Java CDI (Contexts and Dependency Injection) standard introduced in Java EE 6 (JSR-299), read more. Spring has chosen to support using the @Inject annotation synonymously with their own @Autowired annotation.

So, to answer your question, @Autowired is Spring's own annotation. @Inject is part of a Java technology called CDI that defines a standard for dependency injection similar to Spring. In a Spring application, the two annotations work the same way as Spring has decided to support some JSR-299 annotations in addition to their own.

Audreaaudres

So in theory if you used @Inject you could replace spring with another DI framework e.g. Guice and inject your dependencies in the same way. – Okelley

At the risk of being pedantic: @Inject is a separate JSR (JSR-330) from CDI (JSR-299). – Subadar

If you rely on JSR-* annotations only, sure, you can replace you DI framework. But will you? Once you've started using spring, chances are you've used a lot more of it than just DI. You won't just make a change; and even if you do, it's not a few search & replaces that is going to make or break the move. On the other hand, Spring's own annotations offer you a lot more functionality. Mastering a good framework will give you more than hardly using many. – Pouliot

I agree with you that we dont change the DI frameworks often . However if our source code has multiple packages and if you want to build a common package which you want to share across multiple projects and then going with @Inject JSR annotation is better than using @Autowired which locks your code base with spring DI. – Phial

Using @Inject alone won't ensure framework independence. You'd also need to declare injectable beans without framework dependent mechanisms like Spring's @Component or application.xml, but use @Named and @Singleton on class level. No idea if any Spring project really declares beans like that today - I even never heard of any project which migrated from Spring to JEE... – Thirdrate

Please have a look at this link: concretepage.com/spring/… This feature is supported in @Inject automatically without any (required=false) attribute – Inkwell

So I suppose this CDI is not in OpenJDK? – Haematothermal

Answer 2

Here is a blog post that compares @Resource, @Inject, and @Autowired, and appears to do a pretty comprehensive job.

From the link:

With the exception of test 2 & 7 the configuration and outcomes were identical. When I looked under the hood I determined that the ‘@Autowired’ and ‘@Inject’ annotation behave identically. Both of these annotations use the ‘AutowiredAnnotationBeanPostProcessor’ to inject dependencies. ‘@Autowired’ and ‘@Inject’ can be used interchangeable to inject Spring beans. However the ‘@Resource’ annotation uses the ‘CommonAnnotationBeanPostProcessor’ to inject dependencies. Even though they use different post processor classes they all behave nearly identically. Below is a summary of their execution paths.

Tests 2 and 7 that the author references are 'injection by field name' and 'an attempt at resolving a bean using a bad qualifier', respectively.

The Conclusion should give you all the information you need.

Nunez

That article is a great explanation of the the three annotations. I had to re-read it after the first swipe; but, an excellent article. – Byrnes

Thanks a lot! The article answered multiple of my answers in my search of finding the differences and similarities between Spring and JavaEE, as well as a few other questions I had. – Almeida

Please have a look at this link: concretepage.com/spring/… This feature is supported in @Inject automatically without any (required=false) attribute – Inkwell

Answer 3

To handle the situation in which there is no wiring, beans are available with @Autowired required attribute set to false.

But when using @Inject, the Provider interface works with the bean which means that the bean is not injected directly but with the Provider.

Croupier

This is so important, and has been overlooked in the most upvoted answers. – Briticism

By default required parameter is set to true for Autowired. Ref: docs.spring.io/spring-framework/docs/current/javadoc-api/org/… – Iinde

Answer 4

The key difference(noticed when reading the Spring Docs) between @Autowired and @Inject is that, @Autowired has the 'required' attribute while the @Inject has no 'required' attribute.

Colonialism

what do u mean by required? – Baxley

@mattymanme From the docs, "By default, the autowiring fails whenever zero candidate beans are available; the default behavior is to treat annotated methods, constructors, and fields as indicating required dependencies. This behavior can be changed by setting the required attribute to false". E.g: @Autowired(required=false).In simple terms, "The required attribute indicates that the property is not required for autowiring purposes, the property is ignored if it cannot be autowired." – Colonialism

look in to source code public interface Autowired { /** * Declares whether the annotated dependency is required. */ boolean required() default true; } public interface Inject {} – Elliot

Answer 5

As of Spring 3.0, Spring offers support for JSR-330 dependency injection annotations (@Inject, @Named, @Singleton).

There is a separate section in the Spring documentation about them, including comparisons to their Spring equivalents.

Survance

Question here, what do you mean when you say Spring supports JSR? Doesn't the container support JSR independent of Spring, and a requirement for the container to be J2EE compliant? Do you mean that it wraps the functionality? If Spring didn't "support" it, wouldn't the annotation from javax still work by default? – Sonneteer

It's not a must to run Spring in a JEE container, you can also use it in a servlet/JSP container like Tomcat and still have the JSR-330 support. Spring is a separate DI container, it does not "interchange" CDI beans with the host JEE server if its that what you mean. You may either use CDI in a JEE container, or Spring beans - but you can't use both (out of the box). – Survance

Answer 6

In addition to the above:

1. The default scope for @Autowired beans is Singleton whereas using JSR 330 @Inject annotation it is like Spring's prototype.
2. There is no equivalent of @Lazy in JSR 330 using @Inject.
3. There is no equivalent of @Value in JSR 330 using @Inject.

Ozonolysis

Answer 7

@Autowired annotation is defined in the Spring framework.

@Inject annotation is a standard annotation, which is defined in the standard "Dependency Injection for Java" (JSR-330). Spring (since the version 3.0) supports the generalized model of dependency injection which is defined in the standard JSR-330. (Google Guice frameworks and Picocontainer framework also support this model).

With @Inject can be injected the reference to the implementation of the Provider interface, which allows injecting the deferred references.

Annotations @Inject and @Autowired- is almost complete analogies. As well as @Autowired annotation, @Inject annotation can be used for automatic binding properties, methods, and constructors.

In contrast to @Autowired annotation, @Inject annotation has no required attribute. Therefore, if the dependencies will not be found - will be thrown an exception.

There are also differences in the clarifications of the binding properties. If there is ambiguity in the choice of components for the injection the @Named qualifier should be added. In a similar situation for @Autowired annotation will be added @Qualifier qualifier (JSR-330 defines it's own @Qualifier annotation and via this qualifier annotation @Named is defined).

Lamed

Even though the '@Inject' does not have a required attribute the Java Docs state: Injection of members annotated with '@Inject' is required. Which seems to imply that if an member is not found its inject will fail. See Java Docs: docs.oracle.com/javaee/7/api/javax/inject/Inject.html – Camisole

Answer 8

Better use @Inject all the time. Because it is java configuration approach(provided by sun) which makes our application agnostic to the framework. So if you spring also your classes will work.

If you use @Autowired it will works only with spring because @Autowired is spring provided annotation.

Seagraves

Sun is dead. Long live the sun. – Menial

how often are you going to change the framework? just curious – Homeward

On most of projects I saw Autowired rather than Inject. I understand the rationale of the answer but I cannot upvote. – Susansusana

I understand the agnostic approach, but I think at this level it just doesn't work. If you would like to be agnostic, don't use any frameworks, because they ultimately define how you write your code and after that if you prefer to change it, you'll end up with a code future devs will never understand why was it written like that. However on higher levels, like defining the API of your code, I agree with the agnostic approach. "Code for the interface, not for the implementation." – Laser

Answer 9

@Inject has no 'required' attribute

Solnit

What's no 'required'? – Whaling

By writing @Autowired(required = false) you can finish the initialization of your component even if Spring was unable to wire (inject) the member. @Inject will throw an exception in such case, without the opportunity to continue with construction/injection. – Reiko

Answer 10

@Autowired(required=false) By default the dependency injection for @Autowired must be fulfilled because the value of required attribute is true by default. We can change this behavior by using @Autowired(required=false). In this case if bean is not found for dependency injection, it will not through error.

Please have look at https://www.concretepage.com/spring/spring-autowired-annotation#required-false

But @Inject doesn’t need (required=false) it will not through error if dependency is not found

Inkwell

Good and abbreviate explanation But it will thow exception if bean not exists – Hurley

Answer 11

The @Inject annotation is one of the JSR-330 annotations collection. This has Match by Type,Match by Qualifier, Match by Name execution paths. These execution paths are valid for both setter and field injection.The behavior of @Autowired annotation is same as the @Inject annotation. The only difference is the @Autowired annotation is a part of the Spring framework. @Autowired annotation also has the above execution paths. So I recommend the @Autowired for your answer.

Odilo

Answer 12

Inject and Autowired both serves the same functionality i.e to inject the bean.

@Inject - It's defined in the javax.inject package and it's part of Java.
If your application is not spring framework then use Inject annotation as it's part of java.

@Autowired – It's defined in the package org.springframework.bean.factory and part of Spring framework. If your application is Spring based application then better use Autowired annotation.

Sidero