Environment variables for list in spring boot configuration

a bit late for the show but, I was facing the same problem and this solves it

https://github.com/spring-projects/spring-boot/wiki/Relaxed-Binding-2.0#lists-1

MY_FOO_1_ = my.foo[1]

MY_FOO_1_BAR = my.foo[1].bar

MY_FOO_1_2_ = my.foo[1][2]`

So, for the example in the question:

properties:
  topics:
    - 
      name: topic-01
      id: id-1
    - 
      name: topic-02
      id: id-2
    - 
      name: topic-03
      id: id-3

The environment variables should look like this:

PROPERTIES_TOPICS_0_NAME=topic-01
PROPERTIES_TOPICS_0_ID=id-01
PROPERTIES_TOPICS_1_NAME=topic-02
PROPERTIES_TOPICS_1_ID=id-02
PROPERTIES_TOPICS_2_NAME=topic-03
PROPERTIES_TOPICS_2_ID=id-03

Suggestion, don't overcomplicate.

Say you want that list as an Environment variable. You'd set it using

-Dtopics=topic-01,topic-02,topic-03

You then can recover it using the injected Environment Bean, and create a new List<String> Bean

@Bean
@Qualifier("topics")
List<String> topics(final Environment environment) {
    final var topics = environment.getProperty("topics", "");
    return Arrays.asList(topics.split(","));
}

From now on, that List can be @Autowired.
You can also consider creating your custom qualifier annotation, maybe @Topics.

Then

@Service
class TopicService {
   @Topics
   @Autowired
   private List<String> topics;

   ...
}

Or even

@Service
class TopicService {
   private final List<String> topics;

   TopicService(@Topics final List<String> topics) {
      this.topics = topics;
   }

   ...
}

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What you could do is use an externalized file.
Pass to the environment parameters the path to that file.

-DtopicsPath=C:/whatever/path/file.json

Than use the Environment Bean to recover that path. Read the file content and ask Jackson to deserialize it

You'd also need to create a simple Topic class

public class Topic {
    public String name;
    public String id;
}

Which represents an element of this JSON array

[
    {
        "name": "topic-1",
        "id": "id-1"
    },
    {
        "name": "topic-2",
        "id": "id-2"
    }
]

---

@Bean
List<Topic> topics(
        final Environment environment,
        final ObjectMapper objectMapper) throws IOException {
    // Get the file path
    final var topicsPath = environment.getProperty("topicsPath");

    if (topicsPath == null) {
        return Collections.emptyList();
    }

    // Read the file content
    final var json = Files.readString(Paths.get(topicsPath));

    // Convert the JSON to Java objects
    final var topics = objectMapper.readValue(json, Topic[].class);
    return Arrays.asList(topics);
}

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