YAML file : mapping values to Object list with Spring Boot 7

I struggled a bit with a thing that could be so simple. I had a set of rules that I wanted to map as an Object list and documentations was not very clear. So I’ve decided to put my 2 cents, and detail the steps to make it works properly.

To be able to do this, you have to have a Spring Boot project, with SnakeYAML (in much Spring Boot starter projects, the dependancy is already in).

Let’s go

I have a set of rules, that is corresponding to a POJO in my Java project, here is the YAML representation :

configuration.yml

rules: 
     networkRules:
           -
               size: 10
               prefix: '255'
               regex:  '^([ ... some regex])\S$'
            -
               size: 11
               prefix: '180'
               regex: '^([ ... a cool regex ...])\S$'
            -
               size: 10
               prefix: '128'
               regex:  '^([ ... another regex...])\S$'

Your yml file being formatted like this, let’s browse a bit the Java code :

Let’s begin with our object model (the POJO) :

NetworkRule.java

@Data
@NoArgsConstructor
public class NetworkRule {
    
    private int size;
    private String prefix;
    private String regex;

    public NetworkRule(int size, String prefix, String regex) {
        this.size = size;
        this.prefix = prefix;
        this.regex = regex;
    }

    // GETTERS & SETTERS
}

You can create your getters and setters for each of your attributes, I didn’t here because I’m using lombok plugin which let us annotate my class with @Data and generate the whole bunch of getters, setters, toString, hash … methods.

ConfigurationService.java

@Service
@ConfigurationProperties(prefix = "rules")
public class ConfigurationService {
    private List<NetworkRule> networkRules = new ArrayList<>();

    @PostConstruct
    public void init() {
        for(NetworkRule current : this.getNetworkRules()) {
             // DO STUFF, or you can call your get method wherever you want
        }
    }

    public List<NetworkRule> getNetworkRules() {
        return this.networkRules;
    }
}

 Conclusion

I have been fighting with this as I though like @Value(« ${foo} ») , the @ConfigurationProperties would init the object during the construction of my object. But it was not the case, you have to call your getter method on your object list in order to retrieve it.

The most helpful stackoverflow post was this one (I also added an answer :p) : http://stackoverflow.com/questions/32593014/mapping-list-in-yaml-to-list-of-objects-in-spring-boot/34879008#34879008