/*
* Copyright 2002-2020 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.context.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.beans.factory.annotation.Autowire;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.core.annotation.AliasFor;
Indicates that a method produces a bean to be managed by the Spring container.
Overview
The names and semantics of the attributes to this annotation are intentionally similar to those of the <bean/> element in the Spring XML schema. For example:
@Bean
public MyBean myBean() {
// instantiate and configure MyBean obj
return obj;
}
Bean Names
While a name attribute is available, the default strategy for determining the name of a bean is to use the name of the @Bean method. This is convenient and intuitive, but if explicit naming is desired, the name attribute (or its alias value) may be used. Also note that name accepts an array of Strings, allowing for multiple names (i.e. a primary bean name plus one or more aliases) for a single bean.
@Bean({"b1", "b2"}) // bean available as 'b1' and 'b2', but not 'myBean'
public MyBean myBean() {
// instantiate and configure MyBean obj
return obj;
}
Profile, Scope, Lazy, DependsOn, Primary, Order
Note that the @Bean annotation does not provide attributes for profile, scope, lazy, depends-on or primary. Rather, it should be used in conjunction with @Scope, @Lazy, @DependsOn and @Primary annotations to declare those semantics. For example:
@Bean
@Profile("production")
@Scope("prototype")
public MyBean myBean() {
// instantiate and configure MyBean obj
return obj;
}
The semantics of the above-mentioned annotations match their use at the component class level: @Profile allows for selective inclusion of certain beans. @Scope changes the bean's scope from singleton to the specified scope. @Lazy only has an actual effect in case of the default singleton scope. @DependsOn enforces the creation of specific other beans before this bean will be created, in addition to any dependencies that the bean expressed through direct references, which is typically helpful for singleton startup. @Primary is a mechanism to resolve ambiguity at the injection point level if a single target component needs to be injected but several beans match by type. Additionally, @Bean methods may also declare qualifier annotations and @Order values, to be taken into account during injection point resolution just like corresponding annotations on the corresponding component classes but potentially being very individual per bean definition (in case of multiple definitions with the same bean class). Qualifiers narrow the set of candidates after the initial type match; order values determine the order of resolved elements in case of collection injection points (with several target beans matching by type and qualifier).
NOTE: @Order values may influence priorities at injection points, but please be aware that they do not influence singleton startup order which is an orthogonal concern determined by dependency relationships and @DependsOn declarations as mentioned above. Also, Priority is not available at this level since it cannot be declared on methods; its semantics can be modeled through @Order values in combination with @Primary on a single bean per type.
@Bean Methods in @Configuration Classes
Typically, @Bean methods are declared within @Configuration classes. In this case, bean methods may reference other @Bean methods in the same class by calling them directly. This ensures that references between beans
are strongly typed and navigable. Such so-called 'inter-bean references' are guaranteed to respect scoping and AOP semantics, just like getBean() lookups would. These are the semantics known from the original 'Spring JavaConfig' project which require CGLIB subclassing of each such configuration class at runtime. As a consequence, @Configuration classes and their factory methods must not be marked as final or private in this mode. For example:
@Configuration
public class AppConfig {
@Bean
public FooService fooService() {
return new FooService(fooRepository());
}
@Bean
public FooRepository fooRepository() {
return new JdbcFooRepository(dataSource());
}
// ...
}
@Bean Lite Mode
@Bean methods may also be declared within classes that are not annotated with @Configuration. For example, bean methods may be declared in a @Component class or even in a plain old class. In such cases, a @Bean method will get processed in a so-called 'lite' mode.
Bean methods in lite mode will be treated as plain factory
methods by the container (similar to factory-method declarations in XML), with scoping and lifecycle callbacks properly applied. The containing class remains unmodified in this case, and there are no unusual constraints for the containing class or the factory methods.
In contrast to the semantics for bean methods in @Configuration classes, 'inter-bean references' are not supported in lite mode. Instead, when one @Bean-method invokes another @Bean-method in lite mode, the invocation is a standard Java method invocation; Spring does not intercept the invocation via a CGLIB proxy. This is analogous to inter-@Transactional method calls where in proxy mode, Spring does not intercept the invocation — Spring does so only in AspectJ mode.
For example:
@Component
public class Calculator {
public int sum(int a, int b) {
return a+b;
}
@Bean
public MyBean myBean() {
return new MyBean();
}
}
Bootstrapping
See the @Configuration javadoc for further details including how to bootstrap the container using AnnotationConfigApplicationContext and friends.
BeanFactoryPostProcessor-returning @Bean methods
Special consideration must be taken for @Bean methods that return Spring BeanFactoryPostProcessor (BFPP) types. Because BFPP objects must be instantiated very early in the container lifecycle, they can interfere with processing of annotations such as @Autowired, @Value, and @PostConstruct within @Configuration classes. To avoid these lifecycle issues, mark BFPP-returning @Bean methods as static. For example:
@Bean
public static PropertySourcesPlaceholderConfigurer pspc() {
// instantiate, configure and return pspc ...
}
By marking this method as static, it can be invoked without causing instantiation of its declaring @Configuration class, thus avoiding the above-mentioned lifecycle conflicts. Note however that static @Bean methods will not be enhanced for scoping and AOP semantics as mentioned above. This works out in BFPP cases, as they are not typically referenced by other @Bean methods. As a reminder, an INFO-level log message will be issued for any non-static @Bean methods having a return type assignable to BeanFactoryPostProcessor. Author: Rod Johnson, Costin Leau, Chris Beams, Juergen Hoeller, Sam Brannen See Also: Since: 3.0
/**
* Indicates that a method produces a bean to be managed by the Spring container.
*
* <h3>Overview</h3>
*
* <p>The names and semantics of the attributes to this annotation are intentionally
* similar to those of the {@code <bean/>} element in the Spring XML schema. For
* example:
*
* <pre class="code">
* @Bean
* public MyBean myBean() {
* // instantiate and configure MyBean obj
* return obj;
* }
* </pre>
*
* <h3>Bean Names</h3>
*
* <p>While a {@link #name} attribute is available, the default strategy for
* determining the name of a bean is to use the name of the {@code @Bean} method.
* This is convenient and intuitive, but if explicit naming is desired, the
* {@code name} attribute (or its alias {@code value}) may be used. Also note
* that {@code name} accepts an array of Strings, allowing for multiple names
* (i.e. a primary bean name plus one or more aliases) for a single bean.
*
* <pre class="code">
* @Bean({"b1", "b2"}) // bean available as 'b1' and 'b2', but not 'myBean'
* public MyBean myBean() {
* // instantiate and configure MyBean obj
* return obj;
* }
* </pre>
*
* <h3>Profile, Scope, Lazy, DependsOn, Primary, Order</h3>
*
* <p>Note that the {@code @Bean} annotation does not provide attributes for profile,
* scope, lazy, depends-on or primary. Rather, it should be used in conjunction with
* {@link Scope @Scope}, {@link Lazy @Lazy}, {@link DependsOn @DependsOn} and
* {@link Primary @Primary} annotations to declare those semantics. For example:
*
* <pre class="code">
* @Bean
* @Profile("production")
* @Scope("prototype")
* public MyBean myBean() {
* // instantiate and configure MyBean obj
* return obj;
* }
* </pre>
*
* The semantics of the above-mentioned annotations match their use at the component
* class level: {@code @Profile} allows for selective inclusion of certain beans.
* {@code @Scope} changes the bean's scope from singleton to the specified scope.
* {@code @Lazy} only has an actual effect in case of the default singleton scope.
* {@code @DependsOn} enforces the creation of specific other beans before this
* bean will be created, in addition to any dependencies that the bean expressed
* through direct references, which is typically helpful for singleton startup.
* {@code @Primary} is a mechanism to resolve ambiguity at the injection point level
* if a single target component needs to be injected but several beans match by type.
*
* <p>Additionally, {@code @Bean} methods may also declare qualifier annotations
* and {@link org.springframework.core.annotation.Order @Order} values, to be
* taken into account during injection point resolution just like corresponding
* annotations on the corresponding component classes but potentially being very
* individual per bean definition (in case of multiple definitions with the same
* bean class). Qualifiers narrow the set of candidates after the initial type match;
* order values determine the order of resolved elements in case of collection
* injection points (with several target beans matching by type and qualifier).
*
* <p><b>NOTE:</b> {@code @Order} values may influence priorities at injection points,
* but please be aware that they do not influence singleton startup order which is an
* orthogonal concern determined by dependency relationships and {@code @DependsOn}
* declarations as mentioned above. Also, {@link javax.annotation.Priority} is not
* available at this level since it cannot be declared on methods; its semantics can
* be modeled through {@code @Order} values in combination with {@code @Primary} on
* a single bean per type.
*
* <h3>{@code @Bean} Methods in {@code @Configuration} Classes</h3>
*
* <p>Typically, {@code @Bean} methods are declared within {@code @Configuration}
* classes. In this case, bean methods may reference other {@code @Bean} methods in the
* same class by calling them <i>directly</i>. This ensures that references between beans
* are strongly typed and navigable. Such so-called <em>'inter-bean references'</em> are
* guaranteed to respect scoping and AOP semantics, just like {@code getBean()} lookups
* would. These are the semantics known from the original 'Spring JavaConfig' project
* which require CGLIB subclassing of each such configuration class at runtime. As a
* consequence, {@code @Configuration} classes and their factory methods must not be
* marked as final or private in this mode. For example:
*
* <pre class="code">
* @Configuration
* public class AppConfig {
*
* @Bean
* public FooService fooService() {
* return new FooService(fooRepository());
* }
*
* @Bean
* public FooRepository fooRepository() {
* return new JdbcFooRepository(dataSource());
* }
*
* // ...
* }</pre>
*
* <h3>{@code @Bean} <em>Lite</em> Mode</h3>
*
* <p>{@code @Bean} methods may also be declared within classes that are <em>not</em>
* annotated with {@code @Configuration}. For example, bean methods may be declared
* in a {@code @Component} class or even in a <em>plain old class</em>. In such cases,
* a {@code @Bean} method will get processed in a so-called <em>'lite'</em> mode.
*
* <p>Bean methods in <em>lite</em> mode will be treated as plain <em>factory
* methods</em> by the container (similar to {@code factory-method} declarations
* in XML), with scoping and lifecycle callbacks properly applied. The containing
* class remains unmodified in this case, and there are no unusual constraints for
* the containing class or the factory methods.
*
* <p>In contrast to the semantics for bean methods in {@code @Configuration} classes,
* <em>'inter-bean references'</em> are not supported in <em>lite</em> mode. Instead,
* when one {@code @Bean}-method invokes another {@code @Bean}-method in <em>lite</em>
* mode, the invocation is a standard Java method invocation; Spring does not intercept
* the invocation via a CGLIB proxy. This is analogous to inter-{@code @Transactional}
* method calls where in proxy mode, Spring does not intercept the invocation —
* Spring does so only in AspectJ mode.
*
* <p>For example:
*
* <pre class="code">
* @Component
* public class Calculator {
* public int sum(int a, int b) {
* return a+b;
* }
*
* @Bean
* public MyBean myBean() {
* return new MyBean();
* }
* }</pre>
*
* <h3>Bootstrapping</h3>
*
* <p>See the @{@link Configuration} javadoc for further details including how to bootstrap
* the container using {@link AnnotationConfigApplicationContext} and friends.
*
* <h3>{@code BeanFactoryPostProcessor}-returning {@code @Bean} methods</h3>
*
* <p>Special consideration must be taken for {@code @Bean} methods that return Spring
* {@link org.springframework.beans.factory.config.BeanFactoryPostProcessor BeanFactoryPostProcessor}
* ({@code BFPP}) types. Because {@code BFPP} objects must be instantiated very early in the
* container lifecycle, they can interfere with processing of annotations such as {@code @Autowired},
* {@code @Value}, and {@code @PostConstruct} within {@code @Configuration} classes. To avoid these
* lifecycle issues, mark {@code BFPP}-returning {@code @Bean} methods as {@code static}. For example:
*
* <pre class="code">
* @Bean
* public static PropertySourcesPlaceholderConfigurer pspc() {
* // instantiate, configure and return pspc ...
* }
* </pre>
*
* By marking this method as {@code static}, it can be invoked without causing instantiation of its
* declaring {@code @Configuration} class, thus avoiding the above-mentioned lifecycle conflicts.
* Note however that {@code static} {@code @Bean} methods will not be enhanced for scoping and AOP
* semantics as mentioned above. This works out in {@code BFPP} cases, as they are not typically
* referenced by other {@code @Bean} methods. As a reminder, an INFO-level log message will be
* issued for any non-static {@code @Bean} methods having a return type assignable to
* {@code BeanFactoryPostProcessor}.
*
* @author Rod Johnson
* @author Costin Leau
* @author Chris Beams
* @author Juergen Hoeller
* @author Sam Brannen
* @since 3.0
* @see Configuration
* @see Scope
* @see DependsOn
* @see Lazy
* @see Primary
* @see org.springframework.stereotype.Component
* @see org.springframework.beans.factory.annotation.Autowired
* @see org.springframework.beans.factory.annotation.Value
*/
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Bean {
Alias for name. Intended to be used when no other attributes are needed, for example: @Bean("customBeanName").
See Also: Since: 4.3.3
/**
* Alias for {@link #name}.
* <p>Intended to be used when no other attributes are needed, for example:
* {@code @Bean("customBeanName")}.
* @since 4.3.3
* @see #name
*/
@AliasFor("name")
String[] value() default {};
The name of this bean, or if several names, a primary bean name plus aliases.
If left unspecified, the name of the bean is the name of the annotated method.
If specified, the method name is ignored.
The bean name and aliases may also be configured via the value attribute if no other attributes are declared.
See Also:
/**
* The name of this bean, or if several names, a primary bean name plus aliases.
* <p>If left unspecified, the name of the bean is the name of the annotated method.
* If specified, the method name is ignored.
* <p>The bean name and aliases may also be configured via the {@link #value}
* attribute if no other attributes are declared.
* @see #value
*/
@AliasFor("value")
String[] name() default {};
Are dependencies to be injected via convention-based autowiring by name or type?
Note that this autowire mode is just about externally driven autowiring based
on bean property setter methods by convention, analogous to XML bean definitions.
The default mode does allow for annotation-driven autowiring. "no" refers to
externally driven autowiring only, not affecting any autowiring demands that the
bean class itself expresses through annotations.
See Also: - BY_NAME.BY_NAME
- Autowire.BY_TYPE
Deprecated: as of 5.1, since @Bean factory method argument resolution and @Autowired processing supersede name/type-based bean property injection
/**
* Are dependencies to be injected via convention-based autowiring by name or type?
* <p>Note that this autowire mode is just about externally driven autowiring based
* on bean property setter methods by convention, analogous to XML bean definitions.
* <p>The default mode does allow for annotation-driven autowiring. "no" refers to
* externally driven autowiring only, not affecting any autowiring demands that the
* bean class itself expresses through annotations.
* @see Autowire#BY_NAME
* @see Autowire#BY_TYPE
* @deprecated as of 5.1, since {@code @Bean} factory method argument resolution and
* {@code @Autowired} processing supersede name/type-based bean property injection
*/
@Deprecated
Autowire autowire() default Autowire.NO;
Is this bean a candidate for getting autowired into some other bean?
Default is true; set this to false for internal delegates that are not meant to get in the way of beans of the same type in other places.
Since: 5.1
/**
* Is this bean a candidate for getting autowired into some other bean?
* <p>Default is {@code true}; set this to {@code false} for internal delegates
* that are not meant to get in the way of beans of the same type in other places.
* @since 5.1
*/
boolean autowireCandidate() default true;
The optional name of a method to call on the bean instance during initialization.
Not commonly used, given that the method may be called programmatically directly
within the body of a Bean-annotated method.
The default value is "", indicating no init method to be called.
See Also:
/**
* The optional name of a method to call on the bean instance during initialization.
* Not commonly used, given that the method may be called programmatically directly
* within the body of a Bean-annotated method.
* <p>The default value is {@code ""}, indicating no init method to be called.
* @see org.springframework.beans.factory.InitializingBean
* @see org.springframework.context.ConfigurableApplicationContext#refresh()
*/
String initMethod() default "";
The optional name of a method to call on the bean instance upon closing the application context, for example a close() method on a JDBC DataSource implementation, or a Hibernate SessionFactory object. The method must have no arguments but may throw any exception. As a convenience to the user, the container will attempt to infer a destroy method against an object returned from the @Bean method. For example, given an @Bean method returning an Apache Commons DBCP BasicDataSource, the container will notice the close() method available on that object and automatically register it as the destroyMethod. This 'destroy method inference' is currently limited to detecting only public, no-arg methods named 'close' or 'shutdown'. The method may be declared at any level of the inheritance hierarchy and will be detected regardless of the return type of the @Bean method (i.e., detection occurs reflectively against the bean instance itself at creation time).
To disable destroy method inference for a particular @Bean, specify an empty string as the value, e.g. @Bean(destroyMethod=""). Note that the DisposableBean callback interface will nevertheless get detected and the corresponding destroy method invoked: In other words, destroyMethod="" only affects custom close/shutdown methods and Closeable/AutoCloseable declared close methods.
Note: Only invoked on beans whose lifecycle is under the full control of the
factory, which is always the case for singletons but not guaranteed for any
other scope.
See Also:
/**
* The optional name of a method to call on the bean instance upon closing the
* application context, for example a {@code close()} method on a JDBC
* {@code DataSource} implementation, or a Hibernate {@code SessionFactory} object.
* The method must have no arguments but may throw any exception.
* <p>As a convenience to the user, the container will attempt to infer a destroy
* method against an object returned from the {@code @Bean} method. For example, given
* an {@code @Bean} method returning an Apache Commons DBCP {@code BasicDataSource},
* the container will notice the {@code close()} method available on that object and
* automatically register it as the {@code destroyMethod}. This 'destroy method
* inference' is currently limited to detecting only public, no-arg methods named
* 'close' or 'shutdown'. The method may be declared at any level of the inheritance
* hierarchy and will be detected regardless of the return type of the {@code @Bean}
* method (i.e., detection occurs reflectively against the bean instance itself at
* creation time).
* <p>To disable destroy method inference for a particular {@code @Bean}, specify an
* empty string as the value, e.g. {@code @Bean(destroyMethod="")}. Note that the
* {@link org.springframework.beans.factory.DisposableBean} callback interface will
* nevertheless get detected and the corresponding destroy method invoked: In other
* words, {@code destroyMethod=""} only affects custom close/shutdown methods and
* {@link java.io.Closeable}/{@link java.lang.AutoCloseable} declared close methods.
* <p>Note: Only invoked on beans whose lifecycle is under the full control of the
* factory, which is always the case for singletons but not guaranteed for any
* other scope.
* @see org.springframework.beans.factory.DisposableBean
* @see org.springframework.context.ConfigurableApplicationContext#close()
*/
String destroyMethod() default AbstractBeanDefinition.INFER_METHOD;
}