Added JDK and Spring links to Javadoc generation task.

docs/docs.gradle

@@ -69,6 +69,12 @@ task apidocs(type: Javadoc) {
 
 apidocs.options.outputLevel = org.gradle.external.javadoc.JavadocOutputLevel.QUIET
 
+apidocs.options.links = [
+    "http://static.springframework.org/spring/docs/3.0.x/javadoc-api",
+    "http://static.springsource.org/spring-ldap/docs/1.3.x/apidocs/",
+    "http://download.oracle.com/javase/6/docs/api/"
+]
+
 apidocs.options.groups = [
     'Spring Security Core':[
         'org.springframework.security.core*',