gistfile1.txt

apply plugin: 'java'
task allJavadoc(type: Javadoc) {
    group 'Documentation'
    description 'Generates aggregated Javadoc API documentation for the main source code of all projects.'
    
    source = ""
    classpath = ""
   
    destinationDir file("$project.buildDir/docs/javadoc/")
}

subprojects { 
  afterEvaluate { 
    plugins.withType(JavaPlugin).whenPluginAdded {  
    
    }
  } 
}

apply plugin: 'java'
task allJavadoc(type: Javadoc) {
    group 'Documentation'
    description 'Generates aggregated Javadoc API documentation for the main source code of all projects.'

    // calling the source(Object obj) method of SourceTask 
    // http://www.gradle.org/docs/current/javadoc/org/gradle/api/tasks/SourceTask.html#source(java.lang.Object...)
    source { 
       subprojects.collect { child -> child.sourceSets?.main.allJava } 
    } 
    classpath = ...

    destinationDir file("$project.buildDir/docs/javadoc/")
}