Add support for Spring HATEOAS hypermedia in Actuator endpoints

If spring-hateoas is on the classpath and an MvcEndpoint returns a
@responsebody it will be extended and wrapped into a Resource with links.
All the existing endpoints that return sensible JSON data can be extended
this way (i.e. not /logfile). The HAL browser will also be added as an
endpoint if available on the classpath. Finally, asciidocs for the
Actuator endpoints are available as a separate jar file, which if
included in an app will also generate a new (HTTP) endpoint.

Fixes spring-projectsgh-1390

pom.xml

@@ -87,6 +87,7 @@
 				<module>spring-boot-devtools</module>
 				<module>spring-boot-docs</module>
 				<module>spring-boot-starters</module>
+				<module>spring-boot-actuator-docs</module>
 				<module>spring-boot-cli</module>
 			</modules>
 		</profile>

spring-boot-actuator-docs/pom.xml

@@ -0,0 +1,117 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+
+	<artifactId>spring-boot-actuator-docs</artifactId>
+	<packaging>jar</packaging>
+
+	<name>spring-boot-actuator-docs</name>
+	<description>Docs project for Spring Boot</description>
+
+	<parent>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-parent</artifactId>
+		<version>1.3.0.BUILD-SNAPSHOT</version>
+	</parent>
+
+	<properties>
+		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+		<java.version>1.7</java.version>
+	</properties>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-web</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-actuator</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-hateoas</artifactId>
+			<optional>true</optional>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.restdocs</groupId>
+			<artifactId>spring-restdocs</artifactId>
+			<version>1.0.0.M1</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-groovy-templates</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<configuration>
+					<includes>
+						<include>**/*Documentation.java</include>
+					</includes>
+					<systemPropertyVariables>
+						<org.springframework.restdocs.outputDir>${project.build.directory}/generated-snippets</org.springframework.restdocs.outputDir>
+					</systemPropertyVariables>
+				</configuration>
+			</plugin>
+			<plugin>
+				<groupId>org.asciidoctor</groupId>
+				<artifactId>asciidoctor-maven-plugin</artifactId>
+				<version>1.5.2</version>
+				<executions>
+					<execution>
+						<id>generate-docs</id>
+						<phase>prepare-package</phase>
+						<goals>
+							<goal>process-asciidoc</goal>
+						</goals>
+						<configuration>
+							<backend>html</backend>
+							<doctype>book</doctype>
+							<sourceDocumentName>index.adoc</sourceDocumentName>
+							<attributes>
+								<generated>${project.build.directory}/generated-snippets</generated>
+								<docs>${project.build.directory}/../src/main/asciidoc</docs>
+							</attributes>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+			<plugin>
+				<artifactId>maven-resources-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>copy-resources</id>
+						<phase>prepare-package</phase>
+						<goals>
+							<goal>copy-resources</goal>
+						</goals>
+						<configuration>
+							<outputDirectory>${project.build.outputDirectory}/META-INF/resources/spring-boot-actuator/docs</outputDirectory>
+							<resources>
+								<resource>
+									<directory>${project.build.directory}/generated-docs</directory>
+								</resource>
+							</resources>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

spring-boot-actuator-docs/src/main/asciidoc/autoconfig.adoc

@@ -0,0 +1,26 @@
+=== /autoconfig
+
+This endpoint is a report on the Spring Boot Autoconfiguration process
+that happened when your application started up. It lists all the 
+`@Conditional` annotations that were evaluated as the context started
+and in each case it gives an indication of if (and why) the condition
+matched. A positive match results in a bean being included in the context, 
+and a negative result means the opposite (the beans's class may not even 
+be loaded).
+
+The report is split into 2 parts, positive matches first, and then negative.
+If the context is a hierarchy, there is also a separate report on the parent
+context with the same format (and recursively up to the top of the hierarchy).
+
+NOTE: the report is actually about `@Conditional` evaluation not autoconfiguration
+per se, but most autoconfiguration features use `@Conditional` heavily, so there is
+a lot of overlap.
+
+Example curl request:
+include::{generated}/autoconfig/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/autoconfig/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/autoconfig/http-response.adoc[]

spring-boot-actuator-docs/src/main/asciidoc/beans.adoc

@@ -0,0 +1,17 @@
+=== /beans
+
+This endpoint is a report on the Spring Boot `ApplicationContext`. It lists
+the beans in the context and their dependencies, detailing the names and
+concrete classes of each bean.
+
+NOTE: some beans are pure configuration (any class that is annotated
+`@Configuration`).
+
+Example curl request:
+include::{generated}/beans/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/beans/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/beans/http-response.adoc[]

spring-boot-actuator-docs/src/main/asciidoc/configprops.adoc

@@ -0,0 +1,19 @@
+=== /configprops
+
+This endpoint is a report on the Spring Boot `@ConfigurationProperties`
+beans. Beans with this annotation are bound to the `Environment` on
+startup, so they reflect the externalised configuration of the application.
+Beans are listed by name. 
+A bean that is added using `@EnableConfigurationProperties` will have
+a conventional name: `<prefix>.CONFIGURATION_PROPERTIES`, where
+`<prefix>` is the environment key prefix specified in the 
+`@ConfigurationProperties` annotation. 
+
+Example curl request:
+include::{generated}/configprops/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/configprops/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/configprops/http-response.adoc[]

spring-boot-actuator-docs/src/main/asciidoc/dump.adoc

@@ -0,0 +1,19 @@
+=== /dump
+
+This endpoint is a thread dump: the result is a list of threads each with
+their name, monitor state and stack. It is the same information as you would
+get from `kill -3` of a running Java process. Can be very useful for detecting
+issues at runtime, especially sluggish behaviour caused by threads blocked
+by slow or unavailable I/O (e.g. if a connection pool is exhausted).
+
+NOTE: some `SecurityManager` implementations might prevent this endpoint
+from working.
+
+Example curl request:
+include::{generated}/dump/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/dump/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/dump/http-response.adoc[]

spring-boot-actuator-docs/src/main/asciidoc/env.adoc

@@ -0,0 +1,17 @@
+=== /env
+
+This endpoint is a dump of the Spring `Environment`. It lists the active
+profiles and all the `PropertySources` in the `Environment` (the ones that
+are listed first take precedence when binding to `@ConfigurationProperties`
+or `@Value`). Normally you will see the Java `System` properties and the
+OS environment variables in their own `PropertySources` plus any `.properties`
+or `.yml` files used to configure the application on start up.
+
+Example curl request:
+include::{generated}/env/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/env/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/env/http-response.adoc[]

spring-boot-actuator-docs/src/main/asciidoc/health.adoc

@@ -0,0 +1,22 @@
+=== /health
+
+This endpoint is an indication of the health of the application.
+It has an overall status ("UP", "DOWN" etc.), which is the only thing
+you see unless either you are authenticated or the endpoint is marked
+as `sensitive=false` (`endpoints.health.sensitive=false`). 
+
+The HTTP code in the response reflects the status (e.g. "UP" = 200,
+"OUT_OF_SERVICE"=503, "DOWN"=503). The mappings can be changed by
+configuring `endpoints.health.mapping.<STATUS>=XXX`.
+
+Example curl request:
+include::{generated}/health/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/health/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/health/http-response.adoc[]
+
+Example HTTP response with `endpoints.health.sensitive=false`:
+include::{generated}/health/unsensitive/http-response.adoc[]