Order of execution of annotations in Spring

Question

I am trying to load some properties from property files in Spring boot but also want to access them using a list. I am unsure about the order in which the class member will be initialised.

@Getter
@Setter
@ConfigurationProperties
public class ConfigurationM{

   @Value("${propA}")
   private String propA;

   @Value("${propB}")
   private String propB;

   private List<String> list = Collections.unmodifiableList(propA, propB);


}

Does @Value annotation injects value before the list is initialised? How is the order of evaluation determined when the class is loaded while using annotations?

Injection happens when the object is being created. Instead of relying on the order, `@PostConstruct` should better serve your needs here. — Prashant, Feb 27 '21 at 11:32
My proposal to change question title to: "How to initialize a List of String properties in Spring?" — xerx593, Feb 27 '21 at 12:17
better: "how to load (single) properties into a list of string?" — xerx593, Feb 27 '21 at 12:40

xerx593 · Accepted Answer · 2021-02-27T12:28:44.037

Does @Value annotation injects value before the list is initialised?

Unfortunately, no! The "instance initializer"(class/object body) is executed prior to the "constructor", and spring has no chance to inject there anything.

How is the order of evaluation determined when the class is loaded while using annotations?

-> https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans

You could also evict the @PostConstruct with pure spel:

// pure (built-in) SpEL:
@Value("#{{'${propA}', '${propB}'}}")
private List<String> list;
    
// Java < 9
@Value("#{ T(java.util.Arrays).asList('${propA}', '${propB}')}")
private List<String> listJ8;
    
// Java > 8
@Value("#{ T(java.util.List).of('${propA}', '${propB}')}")
private List<String> listJ9;

Order of execution of annotations in Spring

1 Answers1