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.

Answer 1

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.

Answer 2

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.

Answer 3

@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

Answer 4

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.

Answer 5

@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).

Answer 6

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.

Answer 7

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.

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.

Answer 9

@Inject has no 'required' attribute

Answer 10

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.

Answer 11

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.

Answer 12

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.