[springboot] Load Bean Order Isuuse Bean Post Processor

1. Issue
   • when spring boot is boot, each beans are registred by sequentially. Normally spring boot load them each order by follow dependency injection.
   • But sometimes injected bean is not loaded before, then spring boot can’t find target bean infromation.
   • I met this situation at each bean are located in different projects. - Example
   • Engine project has refer to EngineCommon project.
   • Engine project has MessageAdapter Bean, and EngineCommon project has NetworkInit bean.
   • MessageAdapter bean is injected to NetworkInit bean.
   • Engine project has bootRun.
   • In this situation, Spring boot can’t find MessageAdapter bean when NetworkInit bean is loaded while Engine project boot.
2. Reason
   • Because MessageAdapter bean will be loaded after EngineCommon project’s bean are loaded first.
   • Also @Order annotation is not work for setting ordering between them.
3. Solution
   • I make a BeanPostProcessor.
   • Spring’s BeanPostProcessor gives us hooks into the Spring bean lifecycle to modify its configuration.
   • BeanPostProcessor will be acted last step in loaded bean, and it can modify beans before regiser them to spring boot.

/** Engine Project **/

// MessageAdapt.java
// MessageAdapt
public class MessageAdapt{ 
}

// MessageAdaptConfiguration.java
// Bean configuration
@Configuration
public class MessageAdaptConfiguration {

    @Bean
    public MessageAdapt messageAdapt() {
        return new MessageAdapt();
    }
}

/** EngineCommon Project **/

// NetworkInit.java
// NetworkInit
public class NetworkInit{
  private MessageAdapt messageAdapt
  
  /**...omit...**/
  
  public void setNetworkInit(MessageAdapt messageAdapt){
    this.messageAdapt = messageAdapt;
  }
  
    /**...omit...**/
}

// NetworkInitConfiguration.java
// Bean configuration
@Configuration
public class NetwokInitConfiguration {

    @Bean
    public NetworkInit networkInit() {
        return new NetworkInit();
    }
    
    /** Must BeanPostProcessor is registred by bean **/
    @Bean
    public NetworkInitBeanPostProcessor networkInitBeanPostProcessor() {
      return new NetworkInitBeanPostProcessor();
    }
}

//NetworkInitBeanPostProcessor.java
//
public class NetworkInitBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("networkInit")) {
            
            MessageAdapt messageAdapt = applicationContext.getBean(MessageAdapt.class);

            ((NetworkInit) bean).setNetworkInit(messageAdapt);
        }
        return bean;
    }
}

1. Reference
   • https://www.baeldung.com/spring-beanpostprocessor
   • https://jaimemin.tistory.com/2028
   • https://groups.google.com/g/gwt-sl/c/SDb3hd96MZg