Generate javadoc with aggregatedJavadocs option

.gitignore

@@ -140,3 +140,4 @@ classes/
 p2error.txt
 *.bat
 Nukkit/build/resources/main/plugin.yml
+docs/

build.gradle

@@ -48,6 +48,8 @@ version = String.format("%s.%s", rootVersion, buildNumber)
 
 description = rootProject.name
 
+delete "./docs"
+
 subprojects {
     apply plugin: 'java'
     apply plugin: 'maven'
@@ -85,3 +87,20 @@ subprojects {
         maven { url 'https://jitpack.io' }
     }
 }
+
+task aggregatedJavadocs(type: Javadoc, description: 'Generate javadocs from all child projects as if it was a single project', group: 'Documentation') {
+    destinationDir = file("./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
+        }
+    }
+}