@Import

ConfigA.class

@Configuration
public class ConfigA {
   @Bean
   public A a() {
      return new A(); 
   }
}

ConfigB.class

@Configuration
@Import(ConfigA.class)
public class ConfigB {
   @Bean
   public B a() {
      return new A(); 
   }
}

MainApp.class

public static void main(String[] args) {
   ApplicationContext ctx = new AnnotationConfigApplicationContext(ConfigB.class);

   // now both beans A and B will be available...
   A a = ctx.getBean(A.class);
   B b = ctx.getBean(B.class);
}