Spring Configuration Metadata and Properties Quiz: Additional Configuration Metadata

Study Notes

Spring Boot Configuration Metadata

Spring Boot jars include metadata files that provide details of all supported configuration properties.
The metadata files are designed to let IDE developers offer contextual help and "code completion" as users are working with application properties or application.yml files.
The majority of the metadata file is generated automatically at compile time by processing all items annotated with @ConfigurationProperties.
Configuration metadata files are located inside jars under META-INF/spring-configuration-metadata.json.
The metadata files use a JSON format with items categorized under either "groups" or "properties" and additional values hints categorized under "hints".
Each "property" is a configuration item that the user specifies with a given value.
The "groups" are higher level items that do not themselves specify a value but instead provide a contextual grouping for properties.
"Hints" are additional information used to assist the user in configuring a given property.
The metadata can provide additional information such as deprecation notices, valid values, and providers.
You can easily generate your own configuration metadata file from items annotated with @ConfigurationProperties by using the spring-boot-configuration-processor jar.
The jar includes a Java annotation processor which is invoked as your project is compiled.
If you are using AspectJ or Lombok in your project, you need to make sure that the annotation processors run in the correct order.Spring Boot Configuration Properties
Processor dependency allows for classes and methods annotated with @ConfigurationProperties to be picked up by the processor.
If a class has a single parameterized constructor, one property is created per constructor parameter, unless the constructor is annotated with @Autowired.
If the class has a constructor annotated with @ConstructorBinding, one property is created per constructor parameter for that constructor.
Properties are discovered through the presence of standard getters and setters with special handling for collection and map types.
The annotation processor also supports the use of the @Data, @Value, @Getter, and @Setter lombok annotations.
The Javadoc on fields is used to populate the description attribute of properties.
Default values have to be provided statically and cannot be detected for Enums and Collections.
Manual metadata should be provided for cases where the default value could not be detected.
Inner classes are automatically considered as nested properties.
The @NestedConfigurationProperty annotation can be used on a field to indicate that a regular class should be treated as if it were nested.
The annotation processor automatically merges items from additional-spring-configuration-metadata.json into the main metadata file to support custom "hints".
The additional-spring-configuration-metadata.json file has the same format as the regular spring-configuration-metadata.json file and is optional.

Description

Test your knowledge on Spring Boot Configuration Metadata and Properties with this quiz. Learn about the structure and generation of metadata files, the use of JSON format and annotations, and how to provide additional information such as default values and hints. Challenge yourself and see how much you know about working with application properties and YAML files in Spring Boot.