Automatically detect and register nested @Configuration classes [SPR-8186]

[spring-projects-issues]

Chris Beams opened SPR-8186 and commented

The following is now possible in XML as of Spring 3.1 M1:

<beans>
    <bean id="foo" class="Foo">
        <constructor-arg ref="dataSource"/>
    </bean>
    <beans profile="p1">
        <bean id="dataSource" class="..."/>
    </beans>
    <beans profile="p2">
        <bean id="dataSource" class="..."/>
    </beans>
</beans>

The following is a sketch of the equivalent to the above.

@Configuration
public interface DataSourceConfig {
	@Bean DataSource dataSource();
}

@Configuration
public abstract class Config implements DataSourceConfig {

	@Bean
	public Foo foo() {
		return new Foo(dataSource());
	}

	
	@Profile("p1")
	@Configuration
	static class Profile1Config extends Config {
		@Override @Bean
		public DataSource dataSource() {
			return ...;
		}
	}

	@Profile("p2")
	@Configuration
	static class Profile2Config extends Config {
		@Override @Bean
		public DataSource dataSource() {
			return ...;
		}
	}
}

If nested configuration classes are automatically detected, then bootstrapping is as easy as:

ApplicationContext ctx = new AnnotationConfigApplicationContext(Config.class);
Foo foo = ctx.getBean(Foo.class);
// ...

If they are not, then one must register (or @Import) Config, Profile1Config, and Profile2Config, either of which is awkward.

---

Attachments:

• mylyn-context.zip (433.80 kB)

Issue Links:

• Improve support for @Configuration class hierarchies [SPR-8187] #12838 Improve support for @Configuration class hierarchies ("depends on")
• Support introspection of nested classes with ClassMetadata [SPR-8358] #13005 Support introspection of nested classes with ClassMetadata ("depends on")
• Automatically detect and register static nested @FeatureConfiguration classes [SPR-8034] #12689 Automatically detect and register static nested @FeatureConfiguration classes
• Revisit @Bean introspection between @Configuration classes and 'lite' beans [SPR-17206] #21739 Revisit @Bean introspection between @Configuration classes and 'lite' beans

[spring-projects-issues]

Chris Beams commented

Author: Chris Beams <cbeams@vmware.com>
Date:   Fri May 20 13:08:29 2011 +0800

    Register nested @Configuration classes automatically
    
    The following is now possible:
    
    @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();
            }
        }
    }
    
    public static void main(String... args) {
        AnnotationConfigApplicationContext ctx =
            new AnnotationConfigApplicationContext(AppConfig.class);
        ctx.getBean(MyBean.class);     // works
        ctx.getBean(DataSource.class); // works
    }
    
    Notice that the @Import annotation was not used and that only AppConfig
    was registered against the context. By virtue of the fact that
    DatabaseConfig is a member class of AppConfig, it is automatically
    registered when AppConfig is registered. This avoids an awkward and
    redundant @Import annotation when the relationship is already implicitly
    clear.
    
    See @Configuration Javadoc for details.
    
    Issue: SPR-8186