Add Spring-specific styling to Actuator's API documentation

This commit replaces the default Asciidoctor styling with
Spring specific styling.

First, we need to unzip the contents of the Spring Asciidoctor
documentation resources provided by the
`io.spring.docsresources:spring-docs-resources` distribution zip. This
is done in a `/target/refdocs` folder. We then copy all files from
`src/main/asciidoc` to the same location, and then launch the generation
process.

See gh-16326

spring-boot-project/spring-boot-actuator-autoconfigure/pom.xml

@@ -14,6 +14,7 @@
 	<description>Spring Boot Actuator AutoConfigure</description>
 	<properties>
 		<main.basedir>${basedir}/../..</main.basedir>
+		<refdocs.build.directory>${project.build.directory}/refdocs/</refdocs.build.directory>
 	</properties>
 	<dependencies>
 		<!-- Compile -->
@@ -635,6 +636,24 @@
 			</activation>
 			<build>
 				<plugins>
+					<plugin>
+						<groupId>com.googlecode.maven-download-plugin</groupId>
+						<artifactId>download-maven-plugin</artifactId>
+						<executions>
+							<execution>
+								<id>unpack-doc-resources</id>
+								<phase>generate-resources</phase>
+								<goals>
+									<goal>wget</goal>
+								</goals>
+								<configuration>
+									<url>https://repo.spring.io/release/io/spring/docresources/spring-doc-resources/${spring-doc-resources.version}/spring-doc-resources-${spring-doc-resources.version}.zip</url>
+									<unpack>true</unpack>
+									<outputDirectory>${refdocs.build.directory}</outputDirectory>
+								</configuration>
+							</execution>
+						</executions>
+					</plugin>
 					<plugin>
 						<groupId>org.apache.maven.plugins</groupId>
 						<artifactId>maven-antrun-plugin</artifactId>
@@ -732,7 +751,18 @@
 									<goal>process-asciidoc</goal>
 								</goals>
 								<configuration>
-									<backend>html</backend>
+									<backend>html5</backend>
+									<sourceHighlighter>highlight.js</sourceHighlighter>
+									<doctype>book</doctype>
+									<attributes>
+										<highlightjsdir>js/highlight</highlightjsdir>
+										<highlightjs-theme>atom-one-dark-reasonable</highlightjs-theme>
+										<linkcss>true</linkcss>
+										<imagesdir>./images</imagesdir>
+										<icons>font</icons>
+										<stylesdir>css/</stylesdir>
+										<stylesheet>spring.css</stylesheet>
+									</attributes>
 								</configuration>
 							</execution>
 							<execution>
@@ -747,7 +777,8 @@
 							</execution>
 						</executions>
 						<configuration>
-							<sourceDocumentName>index.adoc</sourceDocumentName>
+							<sourceDirectory>${refdocs.build.directory}</sourceDirectory>
+							<outputDirectory>${project.build.directory}/generated-docs/reference/html</outputDirectory>
 							<attributes>
 								<version-type>${version-type}</version-type>
 								<version>${project.version}</version>
@@ -762,6 +793,28 @@
 							</dependency>
 						</dependencies>
 					</plugin>
+					<plugin>
+						<groupId>org.apache.maven.plugins</groupId>
+						<artifactId>maven-resources-plugin</artifactId>
+						<executions>
+							<execution>
+								<id>copy-asciidoc-resources</id>
+								<phase>generate-resources</phase>
+								<goals>
+									<goal>copy-resources</goal>
+								</goals>
+								<configuration>
+									<outputDirectory>${refdocs.build.directory}</outputDirectory>
+									<resources>
+										<resource>
+											<directory>src/main/asciidoc</directory>
+											<filtering>false</filtering>
+										</resource>
+									</resources>
+								</configuration>
+							</execution>
+						</executions>
+					</plugin>
 					<plugin>
 						<groupId>org.codehaus.mojo</groupId>
 						<artifactId>build-helper-maven-plugin</artifactId>

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/asciidoc/index.adoc

@@ -7,6 +7,7 @@ Andy Wilkinson
 :numbered:
 :icons: font
 :hide-uri-scheme:
+:docinfo: shared,private
 
 This API documentation describes Spring Boot Actuators web endpoints.