Using `@Autowired`

JSR 330’s @Inject annotation can be used in place of Spring’s @Autowired annotation in the examples included in this section. See here for more details.

You can apply the @Autowired annotation to constructors, as the following example shows:

Java
Kotlin

public class MovieRecommender {

	private final CustomerPreferenceDao customerPreferenceDao;

	@Autowired
	public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
		this.customerPreferenceDao = customerPreferenceDao;
	}

	// ...
}

class MovieRecommender @Autowired constructor(
	private val customerPreferenceDao: CustomerPreferenceDao)

As of Spring Framework 4.3, an @Autowired annotation on such a constructor is no longer necessary if the target bean defines only one constructor to begin with. However, if several constructors are available and there is no primary/default constructor, at least one of the constructors must be annotated with @Autowired in order to instruct the container which one to use. See the discussion on constructor resolution for details.

You can also apply the @Autowired annotation to traditional setter methods, as the following example shows:

Java
Kotlin

public class SimpleMovieLister {

	private MovieFinder movieFinder;

	@Autowired
	public void setMovieFinder(MovieFinder movieFinder) {
		this.movieFinder = movieFinder;
	}

	// ...
}

class SimpleMovieLister {

	@set:Autowired
	lateinit var movieFinder: MovieFinder

	// ...

}

You can also apply the annotation to methods with arbitrary names and multiple arguments, as the following example shows:

Java
Kotlin

public class MovieRecommender {

	private MovieCatalog movieCatalog;

	private CustomerPreferenceDao customerPreferenceDao;

	@Autowired
	public void prepare(MovieCatalog movieCatalog,
			CustomerPreferenceDao customerPreferenceDao) {
		this.movieCatalog = movieCatalog;
		this.customerPreferenceDao = customerPreferenceDao;
	}

	// ...
}

class MovieRecommender {

	private lateinit var movieCatalog: MovieCatalog

	private lateinit var customerPreferenceDao: CustomerPreferenceDao

	@Autowired
	fun prepare(movieCatalog: MovieCatalog,
				customerPreferenceDao: CustomerPreferenceDao) {
		this.movieCatalog = movieCatalog
		this.customerPreferenceDao = customerPreferenceDao
	}

	// ...
}

You can apply @Autowired to fields as well and even mix it with constructors, as the following example shows:

Java
Kotlin

public class MovieRecommender {

	private final CustomerPreferenceDao customerPreferenceDao;

	@Autowired
	private MovieCatalog movieCatalog;

	@Autowired
	public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
		this.customerPreferenceDao = customerPreferenceDao;
	}

	// ...
}

class MovieRecommender @Autowired constructor(
	private val customerPreferenceDao: CustomerPreferenceDao) {

	@Autowired
	private lateinit var movieCatalog: MovieCatalog

	// ...
}

Make sure that your target components (for example, MovieCatalog or CustomerPreferenceDao) are consistently declared by the type that you use for your @Autowired-annotated injection points. Otherwise, injection may fail due to a "no type match found" error at runtime.

For XML-defined beans or component classes found via classpath scanning, the container usually knows the concrete type up front. However, for @Bean factory methods, you need to make sure that the declared return type is sufficiently expressive. For components that implement several interfaces or for components potentially referred to by their implementation type, consider declaring the most specific return type on your factory method (at least as specific as required by the injection points referring to your bean).

Self Injection

@Autowired also considers self references for injection (that is, references back to the bean that is currently injected).

Note, however, that self injection is a fallback mechanism. Regular dependencies on other components always have precedence. In that sense, self references do not participate in regular autowiring candidate selection and are therefore in particular never primary. On the contrary, they always end up as lowest precedence.

In practice, you should use self references as a last resort only – for example, for calling other methods on the same instance through the bean’s transactional proxy. As an alternative, consider factoring out the affected methods to a separate delegate bean in such a scenario.

Another alternative is to use @Resource, which may obtain a proxy back to the current bean by its unique name.

Trying to inject the results from @Bean methods in the same @Configuration class is effectively a self-reference scenario as well. Either lazily resolve such references in the method signature where it is actually needed (as opposed to an autowired field in the configuration class) or declare the affected @Bean methods as static, decoupling them from the containing configuration class instance and its lifecycle. Otherwise, such beans are only considered in the fallback phase, with matching beans on other configuration classes selected as primary candidates instead (if available).

You can also instruct Spring to provide all beans of a particular type from the ApplicationContext by adding the @Autowired annotation to a field or method that expects an array of that type, as the following example shows:

Java
Kotlin

public class MovieRecommender {

	@Autowired
	private MovieCatalog[] movieCatalogs;

	// ...
}

class MovieRecommender {

	@Autowired
	private lateinit var movieCatalogs: Array<MovieCatalog>

	// ...
}

The same applies for typed collections, as the following example shows:

Java
Kotlin

public class MovieRecommender {

	private Set<MovieCatalog> movieCatalogs;

	@Autowired
	public void setMovieCatalogs(Set<MovieCatalog> movieCatalogs) {
		this.movieCatalogs = movieCatalogs;
	}

	// ...
}

class MovieRecommender {

	@Autowired
	lateinit var movieCatalogs: Set<MovieCatalog>

	// ...
}

Your target beans can implement the org.springframework.core.Ordered interface or use the @Order or standard @Priority annotation if you want items in the array or list to be sorted in a specific order. Otherwise, their order follows the registration order of the corresponding target bean definitions in the container.

You can declare the @Order annotation at the target class level and on @Bean methods, potentially for individual bean definitions (in case of multiple definitions that use the same bean class). @Order values may influence priorities at injection points, but be aware that they do not influence singleton startup order, which is an orthogonal concern determined by dependency relationships and @DependsOn declarations.

Note that @Order annotations on configuration classes just influence the evaluation order within the overall set of configuration classes on startup. Such configuration-level order values do not affect the contained @Bean methods at all. For bean-level ordering, each @Bean method needs to have its own @Order annotation which applies within a set of multiple matches for the specific bean type (as returned by the factory method).

Note that the standard jakarta.annotation.Priority annotation is not available at the @Bean level, since it cannot be declared on methods. Its semantics can be modeled through @Order values in combination with @Primary on a single bean for each type.

Even typed Map instances can be autowired as long as the expected key type is String. The map values contain all beans of the expected type, and the keys contain the corresponding bean names, as the following example shows:

Java
Kotlin

public class MovieRecommender {

	private Map<String, MovieCatalog> movieCatalogs;

	@Autowired
	public void setMovieCatalogs(Map<String, MovieCatalog> movieCatalogs) {
		this.movieCatalogs = movieCatalogs;
	}

	// ...
}

class MovieRecommender {

	@Autowired
	lateinit var movieCatalogs: Map<String, MovieCatalog>

	// ...
}

By default, autowiring fails when no matching candidate beans are available for a given injection point. In the case of a declared array, collection, or map, at least one matching element is expected.

The default behavior is to treat annotated methods and fields as indicating required dependencies. You can change this behavior as demonstrated in the following example, enabling the framework to skip a non-satisfiable injection point through marking it as non-required (i.e., by setting the required attribute in @Autowired to false):

Java
Kotlin

public class SimpleMovieLister {

	private MovieFinder movieFinder;

	@Autowired(required = false)
	public void setMovieFinder(MovieFinder movieFinder) {
		this.movieFinder = movieFinder;
	}

	// ...
}

class SimpleMovieLister {

	@Autowired(required = false)
	var movieFinder: MovieFinder? = null

	// ...
}

A non-required method will not be called at all if its dependency (or one of its dependencies, in case of multiple arguments) is not available. A non-required field will not get populated at all in such cases, leaving its default value in place.

In other words, setting the required attribute to false indicates that the corresponding property is optional for autowiring purposes, and the property will be ignored if it cannot be autowired. This allows properties to be assigned default values that can be optionally overridden via dependency injection.

Injected constructor and factory method arguments are a special case since the required attribute in @Autowired has a somewhat different meaning due to Spring’s constructor resolution algorithm that may potentially deal with multiple constructors. Constructor and factory method arguments are effectively required by default but with a few special rules in a single-constructor scenario, such as multi-element injection points (arrays, collections, maps) resolving to empty instances if no matching beans are available. This allows for a common implementation pattern where all dependencies can be declared in a unique multi-argument constructor — for example, declared as a single public constructor without an @Autowired annotation.

Only one constructor of any given bean class may declare @Autowired with the required attribute set to true, indicating the constructor to autowire when used as a Spring bean. As a consequence, if the required attribute is left at its default value true, only a single constructor may be annotated with @Autowired. If multiple constructors declare the annotation, they will all have to declare required=false in order to be considered as candidates for autowiring (analogous to autowire=constructor in XML). The constructor with the greatest number of dependencies that can be satisfied by matching beans in the Spring container will be chosen. If none of the candidates can be satisfied, then a primary/default constructor (if present) will be used. Similarly, if a class declares multiple constructors but none of them is annotated with @Autowired, then a primary/default constructor (if present) will be used. If a class only declares a single constructor to begin with, it will always be used, even if not annotated. Note that an annotated constructor does not have to be public.

Alternatively, you can express the non-required nature of a particular dependency through Java 8’s java.util.Optional, as the following example shows:

public class SimpleMovieLister {

	@Autowired
	public void setMovieFinder(Optional<MovieFinder> movieFinder) {
		...
	}
}

You can also use a @Nullable annotation (of any kind in any package — for example, javax.annotation.Nullable from JSR-305) or just leverage Kotlin built-in null-safety support:

Java
Kotlin

public class SimpleMovieLister {

	@Autowired
	public void setMovieFinder(@Nullable MovieFinder movieFinder) {
		...
	}
}

class SimpleMovieLister {

	@Autowired
	var movieFinder: MovieFinder? = null

	// ...
}

You can also use @Autowired for interfaces that are well-known resolvable dependencies: BeanFactory, ApplicationContext, Environment, ResourceLoader, ApplicationEventPublisher, and MessageSource. These interfaces and their extended interfaces, such as ConfigurableApplicationContext or ResourcePatternResolver, are automatically resolved, with no special setup necessary. The following example autowires an ApplicationContext object:

Java
Kotlin

public class MovieRecommender {

	@Autowired
	private ApplicationContext context;

	public MovieRecommender() {
	}

	// ...
}

class MovieRecommender {

	@Autowired
	lateinit var context: ApplicationContext

	// ...
}

The @Autowired, @Inject, @Value, and @Resource annotations are handled by Spring BeanPostProcessor implementations. This means that you cannot apply these annotations within your own BeanPostProcessor or BeanFactoryPostProcessor types (if any). These types must be 'wired up' explicitly by using XML or a Spring @Bean method.

Using @Autowired

Using `@Autowired`