/*
* Copyright 2002-2018 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
*
* http://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.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.annotation.AliasFor;
import org.springframework.stereotype.Component;
Indicates that a class declares one or more @Bean methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime, for example: @Configuration
public class AppConfig {
@Bean
public MyBean myBean() {
// instantiate, configure and return bean ...
}
}
Bootstrapping @Configuration classes
Via AnnotationConfigApplicationContext
@Configuration classes are typically bootstrapped using either AnnotationConfigApplicationContext or its web-capable variant,
AnnotationConfigWebApplicationContext. A simple example with the former follows:
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(AppConfig.class);
ctx.refresh();
MyBean myBean = ctx.getBean(MyBean.class);
// use myBean ...
See the AnnotationConfigApplicationContext javadocs for further details, and see
AnnotationConfigWebApplicationContext for web configuration instructions in a Servlet container.
Via Spring <beans> XML
As an alternative to registering @Configuration classes directly against an AnnotationConfigApplicationContext, @Configuration classes may be declared as normal <bean> definitions within Spring XML files:
<beans>
<context:annotation-config/>
<bean class="com.acme.AppConfig"/>
</beans>
In the example above, <context:annotation-config/> is required in order to enable ConfigurationClassPostProcessor and other annotation-related post processors that facilitate handling @Configuration classes.
Via component scanning
@Configuration is meta-annotated with @Component, therefore @Configuration classes are candidates for component scanning (typically using Spring XML's <context:component-scan/> element) and therefore may also take advantage of @Autowired/@Inject like any regular @Component. In particular, if a single constructor is present autowiring semantics will be applied transparently for that constructor:
@Configuration
public class AppConfig {
private final SomeBean someBean;
public AppConfig(SomeBean someBean) {
this.someBean = someBean;
}
// @Bean definition using "SomeBean"
}
@Configuration classes may not only be bootstrapped using component scanning, but may also themselves configure component scanning using the @ComponentScan annotation:
@Configuration
@ComponentScan("com.acme.app.services")
public class AppConfig {
// various @Bean definitions ...
}
See the @ComponentScan javadocs for details.
Working with externalized values
Using the Environment API
Externalized values may be looked up by injecting the Spring Environment into a @Configuration class — for example, using the @Autowired annotation:
@Configuration
public class AppConfig {
@Autowired Environment env;
@Bean
public MyBean myBean() {
MyBean myBean = new MyBean();
myBean.setName(env.getProperty("bean.name"));
return myBean;
}
}
Properties resolved through the Environment reside in one or more "property source" objects, and @Configuration classes may contribute property sources to the Environment object using the @PropertySource annotation:
@Configuration
@PropertySource("classpath:/com/acme/app.properties")
public class AppConfig {
@Inject Environment env;
@Bean
public MyBean myBean() {
return new MyBean(env.getProperty("bean.name"));
}
}
See the Environment and @PropertySource javadocs for further details.
Using the @Value annotation
Externalized values may be injected into @Configuration classes using the @Value annotation:
@Configuration
@PropertySource("classpath:/com/acme/app.properties")
public class AppConfig {
@Value("${bean.name}") String beanName;
@Bean
public MyBean myBean() {
return new MyBean(beanName);
}
}
This approach is often used in conjunction with Spring's
PropertySourcesPlaceholderConfigurer that can be enabled automatically in XML configuration via <context:property-placeholder/> or explicitly in a @Configuration class via a dedicated static @Bean method (see "a note on BeanFactoryPostProcessor-returning @Bean methods" of @Bean's javadocs for details). Note, however, that explicit registration of a PropertySourcesPlaceholderConfigurer via a static @Bean method is typically only required if you need to customize configuration such as the placeholder syntax, etc. Specifically, if no bean post-processor (such as a PropertySourcesPlaceholderConfigurer) has registered an embedded value
resolver for the ApplicationContext, Spring will register a default embedded value resolver which resolves placeholders against property sources registered in the Environment. See the section below on composing @Configuration classes with Spring XML using @ImportResource; see the @Value javadocs; and see the @Bean javadocs for details on working with BeanFactoryPostProcessor types such as PropertySourcesPlaceholderConfigurer.
Composing @Configuration classes
With the @Import annotation
@Configuration classes may be composed using the @Import annotation, similar to the way that <import> works in Spring XML. Because @Configuration objects are managed as Spring beans within the container, imported configurations may be injected — for example, via constructor injection:
@Configuration
public class DatabaseConfig {
@Bean
public DataSource dataSource() {
// instantiate, configure and return DataSource
}
}
@Configuration
@Import(DatabaseConfig.class)
public class AppConfig {
private final DatabaseConfig dataConfig;
public AppConfig(DatabaseConfig dataConfig) {
this.dataConfig = dataConfig;
}
@Bean
public MyBean myBean() {
// reference the dataSource() bean method
return new MyBean(dataConfig.dataSource());
}
}
Now both AppConfig and the imported DatabaseConfig can be bootstrapped by registering only AppConfig against the Spring context:
new AnnotationConfigApplicationContext(AppConfig.class);
With the @Profile annotation
@Configuration classes may be marked with the @Profile annotation to indicate they should be processed only if a given profile or profiles are active:
@Profile("development")
@Configuration
public class EmbeddedDatabaseConfig {
@Bean
public DataSource dataSource() {
// instantiate, configure and return embedded DataSource
}
}
@Profile("production")
@Configuration
public class ProductionDatabaseConfig {
@Bean
public DataSource dataSource() {
// instantiate, configure and return production DataSource
}
}
Alternatively, you may also declare profile conditions at the @Bean method level — for example, for alternative bean variants within the same configuration class:
@Configuration
public class ProfileDatabaseConfig {
@Bean("dataSource")
@Profile("development")
public DataSource embeddedDatabase() { ... }
@Bean("dataSource")
@Profile("production")
public DataSource productionDatabase() { ... }
}
See the @Profile and Environment javadocs for further details.
With Spring XML using the @ImportResource annotation
As mentioned above, @Configuration classes may be declared as regular Spring <bean> definitions within Spring XML files. It is also possible to import Spring XML configuration files into @Configuration classes using the @ImportResource annotation. Bean definitions imported from XML can be injected — for example, using the @Inject annotation:
@Configuration
@ImportResource("classpath:/com/acme/database-config.xml")
public class AppConfig {
@Inject DataSource dataSource; // from XML
@Bean
public MyBean myBean() {
// inject the XML-defined dataSource bean
return new MyBean(this.dataSource);
}
}
With nested @Configuration classes
@Configuration classes may be nested within one another as follows:
@Configuration
public class AppConfig {
@Inject DataSource dataSource;
@Bean
public MyBean myBean() {
return new MyBean(dataSource);
}
@Configuration
static class DatabaseConfig {
@Bean
DataSource dataSource() {
return new EmbeddedDatabaseBuilder().build();
}
}
}
When bootstrapping such an arrangement, only AppConfig need be registered against the application context. By virtue of being a nested @Configuration class, DatabaseConfig will be registered automatically. This avoids the need to use an @Import annotation when the relationship between AppConfig and DatabaseConfig is already implicitly clear.
Note also that nested @Configuration classes can be used to good effect with the @Profile annotation to provide two options of the same bean to the enclosing @Configuration class.
Configuring lazy initialization
By default, @Bean methods will be eagerly instantiated at container bootstrap time. To avoid this, @Configuration may be used in conjunction with the @Lazy annotation to indicate that all @Bean methods declared within the class are by default lazily initialized. Note that @Lazy may be used on individual @Bean methods as well.
Testing support for @Configuration classes
The Spring TestContext framework available in the spring-test module provides the @ContextConfiguration annotation which can accept an array of @Configuration Class objects:
@RunWith(SpringRunner.class)
@ContextConfiguration(classes = {AppConfig.class, DatabaseConfig.class})
public class MyTests {
@Autowired MyBean myBean;
@Autowired DataSource dataSource;
@Test
public void test() {
// assertions against myBean ...
}
}
See the
TestContext framework
reference documentation for details.
Enabling built-in Spring features using @Enable annotations
Spring features such as asynchronous method execution, scheduled task execution, annotation driven transaction management, and even Spring MVC can be enabled and configured from @Configuration classes using their respective "@Enable" annotations. See @EnableAsync, @EnableScheduling, @EnableTransactionManagement, @EnableAspectJAutoProxy, and @EnableWebMvc for details.
Constraints when authoring @Configuration classes
- Configuration classes must be provided as classes (i.e. not as instances returned
from factory methods), allowing for runtime enhancements through a generated subclass.
- Configuration classes must be non-final.
- Configuration classes must be non-local (i.e. may not be declared within a method).
- Any nested configuration classes must be declared as
static. @Bean methods may not in turn create further configuration classes (any such instances will be treated as regular beans, with their configuration annotations remaining undetected).
Author: Rod Johnson, Chris Beams See Also: Since: 3.0
/**
* Indicates that a class declares one or more {@link Bean @Bean} methods and
* may be processed by the Spring container to generate bean definitions and
* service requests for those beans at runtime, for example:
*
* <pre class="code">
* @Configuration
* public class AppConfig {
*
* @Bean
* public MyBean myBean() {
* // instantiate, configure and return bean ...
* }
* }</pre>
*
* <h2>Bootstrapping {@code @Configuration} classes</h2>
*
* <h3>Via {@code AnnotationConfigApplicationContext}</h3>
*
* <p>{@code @Configuration} classes are typically bootstrapped using either
* {@link AnnotationConfigApplicationContext} or its web-capable variant,
* {@link org.springframework.web.context.support.AnnotationConfigWebApplicationContext
* AnnotationConfigWebApplicationContext}. A simple example with the former follows:
*
* <pre class="code">
* AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
* ctx.register(AppConfig.class);
* ctx.refresh();
* MyBean myBean = ctx.getBean(MyBean.class);
* // use myBean ...
* </pre>
*
* <p>See the {@link AnnotationConfigApplicationContext} javadocs for further details, and see
* {@link org.springframework.web.context.support.AnnotationConfigWebApplicationContext
* AnnotationConfigWebApplicationContext} for web configuration instructions in a
* {@code Servlet} container.
*
* <h3>Via Spring {@code <beans>} XML</h3>
*
* <p>As an alternative to registering {@code @Configuration} classes directly against an
* {@code AnnotationConfigApplicationContext}, {@code @Configuration} classes may be
* declared as normal {@code <bean>} definitions within Spring XML files:
*
* <pre class="code">
* <beans>
* <context:annotation-config/>
* <bean class="com.acme.AppConfig"/>
* </beans>
* </pre>
*
* <p>In the example above, {@code <context:annotation-config/>} is required in order to
* enable {@link ConfigurationClassPostProcessor} and other annotation-related
* post processors that facilitate handling {@code @Configuration} classes.
*
* <h3>Via component scanning</h3>
*
* <p>{@code @Configuration} is meta-annotated with {@link Component @Component}, therefore
* {@code @Configuration} classes are candidates for component scanning (typically using
* Spring XML's {@code <context:component-scan/>} element) and therefore may also take
* advantage of {@link Autowired @Autowired}/{@link javax.inject.Inject @Inject}
* like any regular {@code @Component}. In particular, if a single constructor is present
* autowiring semantics will be applied transparently for that constructor:
*
* <pre class="code">
* @Configuration
* public class AppConfig {
*
* private final SomeBean someBean;
*
* public AppConfig(SomeBean someBean) {
* this.someBean = someBean;
* }
*
* // @Bean definition using "SomeBean"
*
* }</pre>
*
* <p>{@code @Configuration} classes may not only be bootstrapped using
* component scanning, but may also themselves <em>configure</em> component scanning using
* the {@link ComponentScan @ComponentScan} annotation:
*
* <pre class="code">
* @Configuration
* @ComponentScan("com.acme.app.services")
* public class AppConfig {
* // various @Bean definitions ...
* }</pre>
*
* <p>See the {@link ComponentScan @ComponentScan} javadocs for details.
*
* <h2>Working with externalized values</h2>
*
* <h3>Using the {@code Environment} API</h3>
*
* <p>Externalized values may be looked up by injecting the Spring
* {@link org.springframework.core.env.Environment} into a {@code @Configuration}
* class — for example, using the {@code @Autowired} annotation:
*
* <pre class="code">
* @Configuration
* public class AppConfig {
*
* @Autowired Environment env;
*
* @Bean
* public MyBean myBean() {
* MyBean myBean = new MyBean();
* myBean.setName(env.getProperty("bean.name"));
* return myBean;
* }
* }</pre>
*
* <p>Properties resolved through the {@code Environment} reside in one or more "property
* source" objects, and {@code @Configuration} classes may contribute property sources to
* the {@code Environment} object using the {@link PropertySource @PropertySource}
* annotation:
*
* <pre class="code">
* @Configuration
* @PropertySource("classpath:/com/acme/app.properties")
* public class AppConfig {
*
* @Inject Environment env;
*
* @Bean
* public MyBean myBean() {
* return new MyBean(env.getProperty("bean.name"));
* }
* }</pre>
*
* <p>See the {@link org.springframework.core.env.Environment Environment}
* and {@link PropertySource @PropertySource} javadocs for further details.
*
* <h3>Using the {@code @Value} annotation</h3>
*
* <p>Externalized values may be injected into {@code @Configuration} classes using
* the {@link Value @Value} annotation:
*
* <pre class="code">
* @Configuration
* @PropertySource("classpath:/com/acme/app.properties")
* public class AppConfig {
*
* @Value("${bean.name}") String beanName;
*
* @Bean
* public MyBean myBean() {
* return new MyBean(beanName);
* }
* }</pre>
*
* <p>This approach is often used in conjunction with Spring's
* {@link org.springframework.context.support.PropertySourcesPlaceholderConfigurer
* PropertySourcesPlaceholderConfigurer} that can be enabled <em>automatically</em>
* in XML configuration via {@code <context:property-placeholder/>} or <em>explicitly</em>
* in a {@code @Configuration} class via a dedicated {@code static} {@code @Bean} method
* (see "a note on BeanFactoryPostProcessor-returning {@code @Bean} methods" of
* {@link Bean @Bean}'s javadocs for details). Note, however, that explicit registration
* of a {@code PropertySourcesPlaceholderConfigurer} via a {@code static} {@code @Bean}
* method is typically only required if you need to customize configuration such as the
* placeholder syntax, etc. Specifically, if no bean post-processor (such as a
* {@code PropertySourcesPlaceholderConfigurer}) has registered an <em>embedded value
* resolver</em> for the {@code ApplicationContext}, Spring will register a default
* <em>embedded value resolver</em> which resolves placeholders against property sources
* registered in the {@code Environment}. See the section below on composing
* {@code @Configuration} classes with Spring XML using {@code @ImportResource}; see
* the {@link Value @Value} javadocs; and see the {@link Bean @Bean} javadocs for details
* on working with {@code BeanFactoryPostProcessor} types such as
* {@code PropertySourcesPlaceholderConfigurer}.
*
* <h2>Composing {@code @Configuration} classes</h2>
*
* <h3>With the {@code @Import} annotation</h3>
*
* <p>{@code @Configuration} classes may be composed using the {@link Import @Import} annotation,
* similar to the way that {@code <import>} works in Spring XML. Because
* {@code @Configuration} objects are managed as Spring beans within the container,
* imported configurations may be injected — for example, via constructor injection:
*
* <pre class="code">
* @Configuration
* public class DatabaseConfig {
*
* @Bean
* public DataSource dataSource() {
* // instantiate, configure and return DataSource
* }
* }
*
* @Configuration
* @Import(DatabaseConfig.class)
* public class AppConfig {
*
* private final DatabaseConfig dataConfig;
*
* public AppConfig(DatabaseConfig dataConfig) {
* this.dataConfig = dataConfig;
* }
*
* @Bean
* public MyBean myBean() {
* // reference the dataSource() bean method
* return new MyBean(dataConfig.dataSource());
* }
* }</pre>
*
* <p>Now both {@code AppConfig} and the imported {@code DatabaseConfig} can be bootstrapped
* by registering only {@code AppConfig} against the Spring context:
*
* <pre class="code">
* new AnnotationConfigApplicationContext(AppConfig.class);</pre>
*
* <h3>With the {@code @Profile} annotation</h3>
*
* <p>{@code @Configuration} classes may be marked with the {@link Profile @Profile} annotation to
* indicate they should be processed only if a given profile or profiles are <em>active</em>:
*
* <pre class="code">
* @Profile("development")
* @Configuration
* public class EmbeddedDatabaseConfig {
*
* @Bean
* public DataSource dataSource() {
* // instantiate, configure and return embedded DataSource
* }
* }
*
* @Profile("production")
* @Configuration
* public class ProductionDatabaseConfig {
*
* @Bean
* public DataSource dataSource() {
* // instantiate, configure and return production DataSource
* }
* }</pre>
*
* <p>Alternatively, you may also declare profile conditions at the {@code @Bean} method level
* — for example, for alternative bean variants within the same configuration class:
*
* <pre class="code">
* @Configuration
* public class ProfileDatabaseConfig {
*
* @Bean("dataSource")
* @Profile("development")
* public DataSource embeddedDatabase() { ... }
*
* @Bean("dataSource")
* @Profile("production")
* public DataSource productionDatabase() { ... }
* }</pre>
*
* <p>See the {@link Profile @Profile} and {@link org.springframework.core.env.Environment}
* javadocs for further details.
*
* <h3>With Spring XML using the {@code @ImportResource} annotation</h3>
*
* <p>As mentioned above, {@code @Configuration} classes may be declared as regular Spring
* {@code <bean>} definitions within Spring XML files. It is also possible to
* import Spring XML configuration files into {@code @Configuration} classes using
* the {@link ImportResource @ImportResource} annotation. Bean definitions imported from
* XML can be injected — for example, using the {@code @Inject} annotation:
*
* <pre class="code">
* @Configuration
* @ImportResource("classpath:/com/acme/database-config.xml")
* public class AppConfig {
*
* @Inject DataSource dataSource; // from XML
*
* @Bean
* public MyBean myBean() {
* // inject the XML-defined dataSource bean
* return new MyBean(this.dataSource);
* }
* }</pre>
*
* <h3>With nested {@code @Configuration} classes</h3>
*
* <p>{@code @Configuration} classes may be nested within one another as follows:
*
* <pre class="code">
* @Configuration
* public class AppConfig {
*
* @Inject DataSource dataSource;
*
* @Bean
* public MyBean myBean() {
* return new MyBean(dataSource);
* }
*
* @Configuration
* static class DatabaseConfig {
* @Bean
* DataSource dataSource() {
* return new EmbeddedDatabaseBuilder().build();
* }
* }
* }</pre>
*
* <p>When bootstrapping such an arrangement, only {@code AppConfig} need be registered
* against the application context. By virtue of being a nested {@code @Configuration}
* class, {@code DatabaseConfig} <em>will be registered automatically</em>. This avoids
* the need to use an {@code @Import} annotation when the relationship between
* {@code AppConfig} and {@code DatabaseConfig} is already implicitly clear.
*
* <p>Note also that nested {@code @Configuration} classes can be used to good effect
* with the {@code @Profile} annotation to provide two options of the same bean to the
* enclosing {@code @Configuration} class.
*
* <h2>Configuring lazy initialization</h2>
*
* <p>By default, {@code @Bean} methods will be <em>eagerly instantiated</em> at container
* bootstrap time. To avoid this, {@code @Configuration} may be used in conjunction with
* the {@link Lazy @Lazy} annotation to indicate that all {@code @Bean} methods declared within
* the class are by default lazily initialized. Note that {@code @Lazy} may be used on
* individual {@code @Bean} methods as well.
*
* <h2>Testing support for {@code @Configuration} classes</h2>
*
* <p>The Spring <em>TestContext framework</em> available in the {@code spring-test} module
* provides the {@code @ContextConfiguration} annotation which can accept an array of
* {@code @Configuration} {@code Class} objects:
*
* <pre class="code">
* @RunWith(SpringRunner.class)
* @ContextConfiguration(classes = {AppConfig.class, DatabaseConfig.class})
* public class MyTests {
*
* @Autowired MyBean myBean;
*
* @Autowired DataSource dataSource;
*
* @Test
* public void test() {
* // assertions against myBean ...
* }
* }</pre>
*
* <p>See the
* <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/testing.html#testcontext-framework">TestContext framework</a>
* reference documentation for details.
*
* <h2>Enabling built-in Spring features using {@code @Enable} annotations</h2>
*
* <p>Spring features such as asynchronous method execution, scheduled task execution,
* annotation driven transaction management, and even Spring MVC can be enabled and
* configured from {@code @Configuration} classes using their respective "{@code @Enable}"
* annotations. See
* {@link org.springframework.scheduling.annotation.EnableAsync @EnableAsync},
* {@link org.springframework.scheduling.annotation.EnableScheduling @EnableScheduling},
* {@link org.springframework.transaction.annotation.EnableTransactionManagement @EnableTransactionManagement},
* {@link org.springframework.context.annotation.EnableAspectJAutoProxy @EnableAspectJAutoProxy},
* and {@link org.springframework.web.servlet.config.annotation.EnableWebMvc @EnableWebMvc}
* for details.
*
* <h2>Constraints when authoring {@code @Configuration} classes</h2>
*
* <ul>
* <li>Configuration classes must be provided as classes (i.e. not as instances returned
* from factory methods), allowing for runtime enhancements through a generated subclass.
* <li>Configuration classes must be non-final.
* <li>Configuration classes must be non-local (i.e. may not be declared within a method).
* <li>Any nested configuration classes must be declared as {@code static}.
* <li>{@code @Bean} methods may not in turn create further configuration classes
* (any such instances will be treated as regular beans, with their configuration
* annotations remaining undetected).
* </ul>
*
* @author Rod Johnson
* @author Chris Beams
* @since 3.0
* @see Bean
* @see Profile
* @see Import
* @see ImportResource
* @see ComponentScan
* @see Lazy
* @see PropertySource
* @see AnnotationConfigApplicationContext
* @see ConfigurationClassPostProcessor
* @see org.springframework.core.env.Environment
* @see org.springframework.test.context.ContextConfiguration
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
Explicitly specify the name of the Spring bean definition associated with the @Configuration class. If left unspecified (the common case), a bean name will be automatically generated. The custom name applies only if the @Configuration class is picked up via component scanning or supplied directly to an AnnotationConfigApplicationContext. If the @Configuration class is registered as a traditional XML bean definition, the name/id of the bean element will take precedence.
See Also: Returns: the explicit component name, if any (or empty String otherwise)
/**
* Explicitly specify the name of the Spring bean definition associated with the
* {@code @Configuration} class. If left unspecified (the common case), a bean
* name will be automatically generated.
* <p>The custom name applies only if the {@code @Configuration} class is picked
* up via component scanning or supplied directly to an
* {@link AnnotationConfigApplicationContext}. If the {@code @Configuration} class
* is registered as a traditional XML bean definition, the name/id of the bean
* element will take precedence.
* @return the explicit component name, if any (or empty String otherwise)
* @see org.springframework.beans.factory.support.DefaultBeanNameGenerator
*/
@AliasFor(annotation = Component.class)
String value() default "";
}