B.3 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)
}

	Note
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 pick up 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.

	Note
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.

Note

If you are using AspectJ in your project, you need to make sure that the annotation processor only runs once. There are several ways to do this: with Maven, you can configure the maven-apt-plugin explicitly and add the dependency to the annotation processor only there. You could also let the AspectJ plugin run all the processing and disable annotation processing in the maven-compiler-plugin configuration:

B.3.1 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.3.2 Adding additional meta-data

Spring Boot’s configuration file handling is quite flexible; and it is often the case that properties may exist that are not bound to a @ConfigurationProperties bean. You may also need to tune some attributes of an existing key. To support such cases and allow you to provide custom "hints", the annotation processor will automatically merge items from META-INF/additional-spring-configuration-metadata.json into the main meta-data file.

If you refer to a property that has been detected automatically, the description, default value and deprecation information are overridden if specified. If the manual property declaration is not identified in the current module, it is added as a brand new property.

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.