How to define default null value in application.ym

问题:

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}}

but it doesn't work.

If the value of test.bar is not defined, set test.foo to null (default value)

I already have spring-el in my dependencies. I don't want to use PropertyPlaceholderConfigurer.setNullValue

It's seem to work in @Value but not in application.yml (see http://farenda.com/spring/spring-inject-null-value/)

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

Thanks

回答1:

@Value

From the document, we can see:

A common use case is to assign default field values using "#{systemProperties.myProp}" style expressions.

It is actually three phases here:

• Spring get the annotation string -- AutowiredAnnotationBeanPostProcessor
• Spring get property value by the annotation meta data -- Environmen
• Spring interpret the property value -- ExpressionParser

User Case

If we define a test.foo in application.yml like you have described:

-- application.yml --
test.foo: ${test.bar:#{null}}

Then, we refer to it in code via @Value, it works as you said.

@Autowired
public A(@Value("test.foo") Object a) {}

But If we get it directly from environment, it will be plain string:

env.getProperty("test.foo")

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