如何在 Spring Boot 的 application.yml 中定义默认空值 [英] How to define default null value in application.yml in Spring Boot
问题描述
我正在尝试使用 SpringBoot 版本 1.3.0.RELEASE 在 application.yml 中将默认值定义为空值.目标是能够使用带有 ConfigurationProperties 注释的类来引用它
I'm trying to define the default value as null value in application.yml with SpringBoot version 1.3.0.RELEASE. The goal is be able to refer it with a class with ConfigurationProperties annotation
-- application.yml --
test.foo: ${test.bar:#{null}}
但它不起作用.
如果test.bar的值没有定义，设置test.foo为null(默认值)
If the value of test.bar is not defined, set test.foo to null (default value)
我的依赖项中已经有了 spring-el.我不想使用 PropertyPlaceholderConfigurer.setNullValue
I already have spring-el in my dependencies. I don't want to use PropertyPlaceholderConfigurer.setNullValue
它似乎在 @Value 中有效，但在 application.yml 中无效(请参阅 http://farenda.com/spring/spring-inject-null-value/)
It's seem to work in @Value but not in application.yml (see http://farenda.com/spring/spring-inject-null-value/)
这是一个错误，或者 yaml 不是为此而设计的?我尝试了 http://yaml.org/type/null.html 中的所有值，但它没有也没有用
It's a bug, or yaml is not designed for that? I tried all values in http://yaml.org/type/null.html but it doesn't worked either
谢谢
推荐答案
@Value
从文档中我们可以看出:
@Value
From the document, we can see:
一个常见的用例是使用#{systemProperties.myProp}"样式表达式分配默认字段值.
A common use case is to assign default field values using "#{systemProperties.myProp}" style expressions.
这里其实是三个阶段:
- Spring获取注解字符串——
AutowiredAnnotationBeanPostProcessor - Spring通过注解元数据获取属性值——
Environmen - Spring解释属性值——
ExpressionParser
如果我们像你描述的那样在 application.yml 中定义一个 test.foo:
If we define a test.foo in application.yml like you have described:
-- application.yml --
test.foo: ${test.bar:#{null}}
然后，我们通过@Value在代码中引用它，就如你所说.
Then, we refer to it in code via @Value, it works as you said.
@Autowired
public A(@Value("test.foo") Object a) {}
但是如果我们直接从 environment 获取它，它将是纯字符串:
But If we get it directly from environment, it will be plain string:
env.getProperty("test.foo")
更多
所以，它是否有效取决于您如何使用它.在获得更多信息之前，我无法提供更多帮助.希望关注相关帖子可能会有所帮助.
More
So, whether it is work or not depends on how did you use it. I can't provide more help before more info. Hope following related post may help.
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