public class BeanOne { 
}

public class BeanTwo {
    public BeanTwo(BeanOne beanOne){
    }
}

@Configuration
public class BeanConfigTest {
    @Bean
    @ConditionalOnMissingBean
    public BeanOne beanOne() {
        System.err.println("帶有@ConditionalOnMissingBean的默認 BeanOne 產生------");
        return new BeanOne();
    }
    @Bean
    public BeanTwo beanTwo() {
        return new BeanTwo(this.beanOne());
    }
}

@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();
       }
   }

@Component
public class BeanOne {
}

public class BeanTwo {
    public BeanTwo(BeanOne beanOne){
    }
}

@Component
//@Configuration
public class BeanConfigTest {
    /**
     * @Bean 創(chuàng)建的默認是單例Bean
     */
    @Bean
    @ConditionalOnMissingBean
    public BeanOne beanOne() {
        System.err.println("帶有@ConditionalOnMissingBean的默認 BeanOne 產生------");
        return new BeanOne();
    }
    @Bean
    public BeanTwo beanTwo() {
        return new BeanTwo(this.beanOne());
    }
}