Repeated meta-data items

B.2 Generating your own meta-data using the annotation processor

You can easily generate your own configuration meta-data 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. To use the processor, simply include ​​spring-boot-configuration-processor​​ as an optional dependency, for example with Maven you would add:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-configuration-processor</artifactId>
    <optional>true</optional>
</dependency>

With Gradle, you can use the ​​propdeps-plugin​​ and specify:

dependencies {
    optional "org.springframework.boot:spring-boot-configuration-processor"
  }

  compileJava.dependsOn(processResources)
}

You need to add ​​compileJava.dependsOn(processResources)​​​ to your build to ensure that resources are processed before code is compiled. Without this directive any ​​additional-spring-configuration-metadata.json​​ files will not be processed.

The processor will pickup both classes and methods that are annotated with ​​@ConfigurationProperties​​​. The Javadoc for field values within configuration classes will be used to populate the ​​description​​ attribute.

You should only use simple text with ​​@ConfigurationProperties​​ field Javadoc since they are not processed before being added to the JSON.

Properties are discovered via the presence of standard getters and setters with special handling for collection types (that will be detected even if only a getter is present). The annotation processor also supports the use of the ​​@Data​​​, ​​@Getter​​​ and ​​@Setter​​ lombok annotations.

B.2.1 Nested properties

The annotation processor will automatically consider inner classes as nested properties. For example, the following class:

@ConfigurationProperties(prefix="server")
public class ServerProperties {

    private String name;

    private Host host;

    // ... getter and setters

    private static class Host {

        private String ip;

        private int port;

        // ... getter and setters

    }

}

Will produce meta-data information for ​​server.name​​​, ​​server.host.ip​​​ and ​​server.host.port​​​ properties. You can use the ​​@NestedConfigurationProperty​​annotation on a field to indicate that a regular (non-inner) class should be treated as if it were nested.

B.2.2 Adding additional meta-data

Spring Boot’s configuration file handling is quite flexible; and it often the case that properties may exist that are not bound to a ​​@ConfigurationProperties​​​ bean. To support such cases, the annotation processor will automatically merge items from ​​META-INF/additional-spring-configuration-metadata.json​​ into the main meta-data file.

The format of the ​​additional-spring-configuration-metadata.json​​​ file is exactly the same as the regular ​​spring-configuration-metadata.json​​. The additional properties file is optional, if you don’t have any additional properties, simply don’t add it.