如何在Spring Boot中在application.yml中定义默认的空值 [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。该目标可以使用带有 ConfigurationProperties 批注的类
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 的值不正确定义后，将 test.foo 设置为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spring-el了。我不想使用 PropertyPlaceholderConfigurer.setNullValue
I already have spring-el in my dependencies. I don't want to use PropertyPlaceholderConfigurer.setNullValue
在中似乎可以使用值，但不在 application.yml 中（请参见 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，还是yaml不是为此设计的？
我尝试了 http://yaml.org/type/null.html，但它也不起作用
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
@值
从文档中，我们可以看到：
@Value
From the document, we can see:
一个常见用例是使用＃{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.
此处实际上分为三个阶段：
It is actually three phases here:
- Spring获得注释字符串-
AutowiredAnnotationBeanPostProcessor - Spring通过注释元数据获取属性值-
环境 - Spring解释属性值-
ExpressionParser
- Spring get the annotation string --
AutowiredAnnotationBeanPostProcessor - Spring get property value by the annotation meta data --
Environmen - Spring interpret the property value --
ExpressionParser
如果我们在 application.yml 中定义了 test.foo ，就像您描述的那样：
If we define a test.foo in application.yml like you have described:
-- application.yml --
test.foo: ${test.bar:#{null}}
然后，我们在代码中通过 @Value ，如您所说。
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环境获取它，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
因此，是否起作用取决于您如何使用它。在提供更多信息之前，我无法提供更多帮助。希望后面的相关帖子可能会对您有所帮助。
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.
- Spring EL tutorial
- Spring Boot: customize environment
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