Inject a Map<String, List<String>> using Spring's @Value

Question

I have a properties file that contains a map with keys that each have multiple values, like below

//properties.yml
myMap:
  key1: value1, value2
  key2: value1, value2, value3

It is fairly easy to read myMap using a Spring properties class as follows:

@Configuration
@ConfigurationProperties
public class MyConfiguration {
  private Map<String, List<String>> myMap;

  public Map<String, List<String>> getMyMap() {
      return myMap;
  }

  public void setMyMap(Map<String, List<String>> myMap) {
      this.myMap = myMap;
  }
}

However this feels like a lot of code for a simple task. I was wondering if there is a way to achieve the same thing using Spring's @Value annotation? I've tried to get it to work without success, trying things like

@Value("${myMap}")
private Map<String, List<String>> myMap;

I think maybe it requires SPEL but I'm not sure how

Answer 1

To Inject Map using @Value you can do (but maybe you need to modify your YAML):

@Value("#{${myMap}}")
private Map<String, List<String>> myMap;

However, It is encouraged to use @ConfigurationProperties instead of @Value (especially if you use YAML format, Spring boot uses SnakeYAML to parse YAML files)

https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html#boot-features-external-config-typesafe-configuration-properties

You don't need a setter when loading to the map:

@ConfigurationProperties
public class MapProperties {

    private Map<String, List<String>> myMap = new HashMap<>();

    public Map<String, List<String>> getMyMap() {
        return this.myMap;
    }
}