Can I generate the spring boot configuration metadata as a .properties file

Question

If I include spring-boot-configuration-processor as a dependency, my build will produce a json file like this:

{
  "groups": [
    {
      "name": "attachments",
      "type": "com.example.config.AttachmentsSettings",
      "sourceType": "com.example.config.AttachmentsSettings"
    }
  ],
  "properties": [
    {
      "name": "attachments.max-size",
      "type": "java.lang.Integer",
      "sourceType": "com.example.config.AttachmentsSettings",
      "defaultValue": 1024
    },
    {
      "name": "attachments.min-size",
      "type": "java.lang.Integer",
      "sourceType": "com.example.config.AttachmentsSettings"
    },
    {
      "name": "attachments.invalid-chars",
      "type": "java.lang.String",
      "sourceType": "com.example.config.AttachmentsSettings",
      "defaultValue": "abc"
    }
  ],
  "hints": []
}

I want to additionally produce a properties file that lists all the properties with their default values like this:

attachments.max-size=1024
attachments.invalid-chars=abc
# attachments.min-size=

Ideally, I'd also like it to list the properties that don't have a default value, but commented out.

Is it possible to do something like this already using Spring Boot? Or will I need to write something myself?

whistling_marmot · Answer 1 · 2020-03-10T13:47:12.490

I can extend the ConfigurationMetadataAnnotationProcessor like this:

@SupportedAnnotationTypes({ "*" })
public class MyConfigurationMetadataAnnotationProcessor extends ConfigurationMetadataAnnotationProcessor {

    @Override
    public synchronized void init(ProcessingEnvironment env) {
        super.init(env);

        Field metadataStoreField = ReflectionUtils.findField(ConfigurationMetadataAnnotationProcessor.class, "metadataStore");
        ReflectionUtils.makeAccessible(metadataStoreField);
        ReflectionUtils.setField(metadataStoreField, this, new MyMetadataStore(env));
    }

    private class MyMetadataStore extends MetadataStore {

        static final String METADATA_PROPERTIES_PATH = "META-INF/spring-configuration-metadata.properties";
        private final ProcessingEnvironment environment;

        public MyMetadataStore(ProcessingEnvironment environment) {
            super(environment);
            this.environment = environment;
        }

        @Override
        public void writeMetadata(ConfigurationMetadata metadata) throws IOException {
            if (!metadata.getItems().isEmpty()) {
                try (OutputStream outputStream = createMetadataPropertiesResource().openOutputStream()) {
                    outputStream.write(getProps(metadata).getBytes(StandardCharsets.UTF_8));
                }
            }
        }

        private String getProps(ConfigurationMetadata metadata) {
            return metadata.getItems().stream()
                    .filter(item -> item.isOfItemType(ItemMetadata.ItemType.PROPERTY))
                    .map(item -> nonNull(item.getDefaultValue()) ?
                            item.getName() + "=" + item.getDefaultValue() :
                            "# " + item.getName() + "=")
                    .collect(Collectors.joining("\n"));
        }

        private FileObject createMetadataPropertiesResource() throws IOException {
            return this.environment.getFiler().createResource(StandardLocation.CLASS_OUTPUT, "", METADATA_PROPERTIES_PATH);
        }
    }
}

Then add it as a service in the META-INF directory:

where the Processor file has a single line: com.my.package.MyConfigurationMetadataAnnotationProcessor

I need to compile it in 2 stages - first compile the processor class, then use it to process the annotations - as described in this SO answer.

Can I generate the spring boot configuration metadata as a .properties file

1 Answers1