Here’s a version I use that is smart enough to know what plugins are applied:
task aggregatedJavadocs(type: Javadoc, description: 'Generate javadocs from all child projects as if it was a single project', group: 'Documentation') {
destinationDir = file("$buildDir/docs/javadoc")
title = "$project.name $version API"
options.author true
options.links 'http://docs.spring.io/spring/docs/4.3.x/javadoc-api/', 'http://docs.oracle.com/javase/8/docs/api/', 'http://docs.spring.io/spring-ws/docs/2.3.0.RELEASE/api/', 'http://docs.spring.io/spring-security/site/docs/4.0.4.RELEASE/apidocs/'
options.addStringOption 'Xdoclint:none', '-quiet'
subprojects.each { proj ->
proj.tasks.withType(Javadoc).each { javadocTask ->
source += javadocTask.source
classpath += javadocTask.classpath
excludes += javadocTask.excludes
includes += javadocTask.includes
}
}
}