Add EPUB output

Add EPUB output and make all four output formats have links to one another,
to enable discoverability and accessibility (for the folks who need a
particular format to help them read the document).

pom.xml

@@ -21,7 +21,7 @@
 		<module>spring-batch-jsr352-tck</module>
 		<module>spring-batch-docs</module>
 	</modules>
-	
+
 	<organization>
 		<name>Spring</name>
 		<url>https://spring.io</url>
@@ -113,10 +113,11 @@
 		<quartz.version>2.3.2</quartz.version>
 		<prometheus_pushgateway.version>0.10.0</prometheus_pushgateway.version>
 		<groovy.version>2.5.14</groovy.version>
-		
+
 		<!-- documentation dependencies -->
 		<spring-doc-resources.version>0.2.5</spring-doc-resources.version>
 		<asciidoctorj-pdf.version>1.5.4</asciidoctorj-pdf.version>
+		<asciidoctorj-epub.version>1.5.1</asciidoctorj-epub.version>
 
 		<!-- plugin versions -->
 		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
@@ -276,7 +277,7 @@
 			</plugin>
 		</plugins>
 	</build>
-	
+
 	<profiles>
 		<profile>
 			<id>test-coverage</id>
@@ -334,7 +335,7 @@
 			</build>
 		</profile>
 	</profiles>
-	
+
 	<repositories>
 		<repository>
 			<id>maven-central</id>
@@ -385,7 +386,7 @@
 			</snapshots>
 		</pluginRepository>
 	</pluginRepositories>
-	
+
 	<developers>
 		<developer>
 			<id>dsyer</id>

spring-batch-docs/pom.xml

@@ -18,7 +18,7 @@
             <type>zip</type>
         </dependency>
     </dependencies>
-    
+
     <build>
         <resources>
             <resource>
@@ -66,6 +66,11 @@
                         <artifactId>asciidoctorj-pdf</artifactId>
                         <version>${asciidoctorj-pdf.version}</version>
                     </dependency>
+                    <dependency>
+                        <groupId>org.asciidoctor</groupId>
+                        <artifactId>asciidoctorj-epub3</artifactId>
+                        <version>${asciidoctorj-epub.version}</version>
+                    </dependency>
                 </dependencies>
                 <configuration>
                     <sourceDirectory>${project.basedir}/src/main/asciidoc</sourceDirectory>
@@ -120,6 +125,27 @@
                             </attributes>
                         </configuration>
                     </execution>
+                    <execution>
+                        <id>generate-epub</id>
+                        <phase>site</phase>
+                        <goals>
+                            <goal>process-asciidoc</goal>
+                        </goals>
+                        <configuration>
+                            <backend>epub3</backend>
+                            <doctype>book</doctype>
+                            <attributes>
+                                <icons>font</icons>
+                                <pagenums />
+                                <sectnums />
+                                <sectanchors />
+                                <toc />
+                                <source-highlighter>coderay</source-highlighter>
+                                <project-version>${project.version}</project-version>
+                                <revnumber>${project.version}</revnumber>
+                            </attributes>
+                        </configuration>
+                    </execution>
                 </executions>
             </plugin>
             <plugin>
@@ -155,7 +181,7 @@
             </plugin>
         </plugins>
     </build>
-    
+
     <repositories>
         <repository>
             <id>spring-releases</id>
@@ -167,4 +193,4 @@
         </repository>
     </repositories>
 
-</project>
+</project>

spring-batch-docs/src/assembly/docs.xml

@@ -28,5 +28,10 @@
 			<destName>spring-batch-reference.pdf</destName>
 			<outputDirectory>reference/pdf</outputDirectory>
 		</file>
+		<file>
+			<source>target/asciidoc/index-single.epub</source>
+			<destName>spring-batch-reference.epub</destName>
+			<outputDirectory>reference/epub</outputDirectory>
+		</file>
 	</files>
 </assembly>

spring-batch-docs/src/main/asciidoc/index.adoc

@@ -2,8 +2,9 @@ include::header/index-header.adoc[]
 
 // ======================================================================================
 
-Welcome to the Spring Batch reference documentation! This documentation is also available
-as single link:index-single.html[html] and link:../pdf/spring-batch-reference.pdf[pdf] documents.
+This documentation is also available
+as a link:index-single.html[single HTML file] and as link:../pdf/spring-batch-reference.pdf[PDF]
+and link:../epub/spring-batch-reference.epub[EPUB] documents.
 
 The reference documentation is divided into several sections:
 

spring-batch-docs/src/main/asciidoc/spring-batch-intro.adoc

@@ -2,8 +2,25 @@
 :toc: left
 :toclevels: 4
 
-[[spring-batch-intro]]
+ifdef::backend-html5[]
+This documentation is also available
+as link:index.html[multiple HTML files] and as link:../pdf/spring-batch-reference.pdf[PDF]
+and link:../epub/spring-batch-reference.epub[EPUB] documents.
+endif::[]
 
+ifdef::backend-pdf[]
+This documentation is also available
+as link:index.html[multiple HTML files], a link:index-single.html[single HTML file],
+and an link:../epub/spring-batch-reference.epub[EPUB] document.
+endif::[]
+
+ifdef::backend-epub3[]
+This documentation is also available
+as link:index.html[multiple HTML files], a link:index-single.html[single HTML file],
+and a link:../pdf/spring-batch-reference.pdf[PDF] document.
+endif::[]
+
+[[spring-batch-intro]]
 == Spring Batch Introduction
 
 Many applications within the enterprise domain require bulk processing to perform