javaspringspring-bootjavabeansconstructor-injection

Spring Bean od properties Map<String, POJO> in @Configuration class is visible in class when @Bean method is executing, but not in constructor

A have simple @Configuration class:

@Data //setters and getters
@ComponentScan
@Configuration
@ConfigurationProperties(prefix = "some.prefix")
public class SomeAutoConfig {

    public SomeAutoConfig(Map<String, Pojo> properties) {
        this.properties= properties;
    }

    private final Map<String, Pojo> properties;

    @Bean
    String string() {
        return "test string";
    }

}

On debug I have breakpoints on constructor(this.properties= properties), and @Bean method(return "test string").

I don't see properties as constructor parameter, but in @Bean method there are visible.

Why are there see properties only then? Is good way to Iinject this bean better and can be accisible from constructor too?

Solution

  • This is because Spring initializes this field via setter, between constructor execution and the call to the @Bean annotated method. AFAIK, there's no direct way to do this via constructor, you could use @Value("#{${some.prefix}}"), but this would require to define properties peculiarly, i.e. {key1:'value1',key2:'value2',....}

    EDIT: Since Springboot 2.2, you can leverage @ConstructorBinding annotation.