SpringBoot import config属性加载顺序踩坑

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背景

SpringBoot2.4.0添加了spring.config.import配置项，可以在配置文件里导入其他配置文件，通常用来抽取一些所有profile都会使用的配置，比如公共服务器之类的，下面用一个demo项目演示一下。

复现

首先有3个配置文件

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# application-base.yml
common:
  name: zsh
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# application-dev.yml
spring:
  config:
    import: application-base.yml
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# application-prod.yml
spring:
  config:
    import: application-base.yml

然后指定profile为dev运行，打印common.name配置的值

结果

可以看到打印出了我们配置的值。

问题

很多时候我们希望在active profile里覆盖公共的一些配置，比如MySQL url之类的，这里我们覆盖common.name，把上面3个配置文件稍作修改

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# application-dev.yml
spring:
  config:
    import: application-base.yml

common:
  name: from dev

然后再次运行

结果

奇怪的事情发生了，运行的结果并没有按照我们希望的输出”from dev”，依然还是”zsh”，这是为什么呢？我们来翻一下SpringBoot官方的说明：

Imports can be considered as additional documents inserted just below the document that declares them. They follow the same top-down ordering as regular multi-document files: An import will only be imported once, no matter how many times it is declared.

粗看官方的解释，第一反应是SpringBoot会按照下面的方式转换导入的配置文件

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# application-dev.yml
# before
spring:
  config:
    import: application-base.yml

common:
  name: from dev
# after
spring:
  config:
    import: application-base.yml
common:
	name: zsh
common:
  name: from dev

按照上面的行为，最后打印出来的应该是”from dev”，但是实际结果好像是下面这样

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# application-dev.yml
# before
spring:
  config:
    import: application-base.yml

common:
  name: from dev
# after
spring:
  config:
    import: application-base.yml

common:
  name: from dev
  
common:
	name: zsh

于是我又去翻官方有关回答，找到了下面一段解释

In that example you only actually have one spring.config.import statement. The second one in the properties file will replace the first.

Imports will always happen in the order that they are specified, but the granularity is the current document being processed. So in your example, it wouldn’t matter if you had:

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spring.config.import=my.propertiesmy.property=value

or

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my.property=valuespring.config.import=my.properties

The result is the same. The [my.property](http://disq.us/url?url=http%3A%2F%2Fmy.property%3A3zPwzcFT2x4NYuqlf_XVTdE2BeE&cuid=2935315) value will be anotherValue.

When working on the design, I liked to visualize this a deck of cards. As we read the files, we build up a stack of cards. The first card we process has a spring.config.import statement of [my.properties](http://disq.us/url?url=http%3A%2F%2Fmy.properties%3AeHnV6OOS4iwu4hgYpanuM02s270&cuid=2935315). You go and fetch the “my.properties“ card and place it on top. When you’re done, there’s a stack of cards and the first one you find containing the property name you want will win. I hope that helps, and doesn’t make things more confusing :)

明确说明import config的配置会覆盖当前配置文件中的配置。

结论

如果你的项目存在多套配置文件，且有公共配置文件，注意千万不要把会被覆盖的配置写在公共配置文件内，不然其他引用了公共配置文件的配置文件，将无法覆盖此配置，因此如果某个配置存在被覆盖的可能，请将它单独写在每个启动时引用的配置文件内。