SpringBoot自动装配子属性时如何继承父级配置属性？

我有一个Java SpringBoot应用，application.yaml配置如下，其中timeOut和retryCount是myEventhub1与someEventHub的公共属性：

azure:
  eventhub:
    timeOut: ${timeOut}
    retryCount: ${retryCount}
    myEventhub1:
      eventhubName: ${myEventhubName}
      sasKeyName: ${myEventhubKeyName}
      sasKeyValue: ${myEventhubKey}
    someEventHub: 
      eventhubName: ${someEventhubName}
      sasKeyName: ${someEventhubKeyName}
      sasKeyValue: ${someEventhubKey}

第三方库提供了无法修改的类：

public class EventhubSettings {
    private String eventhubName;
    private String sasKeyName;
    private String sasKeyValue;
    private int retryCount;
    private int timeOut;

    // 第三方类自带getter/setter方法
}

自定义配置类如下：

@Getter
@Setter
@Configuration
@ConfigurationProperties("azure.eventhub")
public class MyEventhubConfig {
    private EventhubSettings myEventhub1;
    private EventhubSettings someEventHub;
}

需要实现MyEventhubConfig中的myEventhub1和someEventHub自动继承父级azure.eventhub下的retryCount和timeOut属性，避免在子节点下重复配置这两个属性。

方法1：配置类初始化时手动填充公共属性 #

修改MyEventhubConfig，新增父级公共属性的字段，通过@PostConstruct在配置初始化后，将父级属性填充到子配置对象中（保留子节点单独配置的优先级）：

@Getter
@Setter
@Configuration
@ConfigurationProperties("azure.eventhub")
public class MyEventhubConfig {
    // 父级公共属性
    private int timeOut;
    private int retryCount;
    
    private EventhubSettings myEventhub1;
    private EventhubSettings someEventHub;

    @PostConstruct
    public void fillCommonProperties() {
        // 为myEventhub1填充公共属性
        if (myEventhub1 != null) {
            if (myEventhub1.getRetryCount() == 0) { // 根据第三方类默认值调整判断逻辑
                myEventhub1.setRetryCount(retryCount);
            }
            if (myEventhub1.getTimeOut() == 0) {
                myEventhub1.setTimeOut(timeOut);
            }
        }
        // 为someEventHub填充公共属性
        if (someEventHub != null) {
            if (someEventHub.getRetryCount() == 0) {
                someEventHub.setRetryCount(retryCount);
            }
            if (someEventHub.getTimeOut() == 0) {
                someEventHub.setTimeOut(timeOut);
            }
        }
    }
}

方法2：YAML锚点复用公共配置 #

无需修改Java代码，直接在application.yaml中使用YAML的锚点和合并语法，复用公共属性：

azure:
  eventhub:
    &commonProps
    timeOut: ${timeOut}
    retryCount: ${retryCount}
    myEventhub1:
      <<: *commonProps
      eventhubName: ${myEventhubName}
      sasKeyName: ${myEventhubKeyName}
      sasKeyValue: ${myEventhubKey}
    someEventHub: 
      <<: *commonProps
      eventhubName: ${someEventhubName}
      sasKeyName: ${someEventhubKeyName}
      sasKeyValue: ${someEventhubKey}

&commonProps定义公共属性锚点，<<: *commonProps将锚点属性合并到当前子节点，子节点也可以单独覆盖timeOut或retryCount实现个性化配置。

方法3：自定义Bean后置处理器（批量处理场景） #

如果有多个类似配置需要处理，可自定义BeanPostProcessor，在配置类初始化后自动填充公共属性：

@Component
public class EventhubSettingsBindingPostProcessor implements BeanPostProcessor {

    @Autowired
    private Environment environment;

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof MyEventhubConfig) {
            MyEventhubConfig config = (MyEventhubConfig) bean;
            // 从环境中读取父级公共属性
            int timeOut = environment.getProperty("azure.eventhub.timeOut", Integer.class, 0);
            int retryCount = environment.getProperty("azure.eventhub.retryCount", Integer.class, 0);
            
            fillSettings(config.getMyEventhub1(), timeOut, retryCount);
            fillSettings(config.getSomeEventHub(), timeOut, retryCount);
        }
        return bean;
    }

    private void fillSettings(EventhubSettings settings, int timeOut, int retryCount) {
        if (settings == null) return;
        if (settings.getRetryCount() == 0) {
            settings.setRetryCount(retryCount);
        }
        if (settings.getTimeOut() == 0) {
            settings.setTimeOut(timeOut);
        }
    }
}

内容的提问来源于stack exchange，提问作者user29454562