@ConfigurationProperties: Default value in bound class

Question

I have a config class FooConfig, in which i have a bound class 'Foo'.

@Configuration
@ConfigurationProperties("foo")
public class FooConfig {

  @Value("${foo.default.iterations}")
  private Integer iterations;

  private Foo foo;

  // getter / setter

}

In my class Foo I want the iterations-variable set with an existing default configuration-value, when not explicitly set in the properties-file.

public class Foo {

  private String name;

  @Value("${foo.default.iterations}")
  private Integer iterations;

  // getter / setter

}

My properties file

foo.default.iterations=999

# if this is set this config is bound (wins) in FooConfig-class as expected
# foo.iterations=111

foo.foo.name=foo

Setting a default value in FooConfig works, but not in my bound class Foo.

What am I missing here?

Answer 1

You shouldn't mix @Value and @ConfigurationProperties in the same class. If you want to have default values in a @ConfigurationProperties-annotated class, you can configure the fields with a default value:

@ConfigurationProperties("foo")
public class FooConfig {

    private Integer iterations = 999;

    // getter / setter

}

This change brings with it the added benefit of including the default value in the metadata that's generated by spring-boot-configuration-processor. The metadata is used by your IDE to provide auto-completion when you're editing application.properties and application.yaml files.

Lastly, and not directly related to your problem, a @ConfigurationProperties-annotated class should not be annotated with @Configuration. An @Configuration-annotated class is used to configure beans via @Bean methods. Your FooConfig class should either be annotated with @Component or you should use @EnableConfigurationProperties(FooConfig.class) on the @Configuration class that wants to use FooConfig.