title: Good ACL implementation in Java
body: <p>I'm implementing a web based document management system and I'd like to implement ACLs in my system.
  My formal requirements are hierarchal permissions (documents inherit permissions from their folders) user groups (users can dynamically create groups and associate users with groups). Such groups can have permissions on objects in the system.</p>
  
  <p>My code will query permission on objects in two cases: 
  1. Manipulating a single document
  2. Listing all documents where a manipulation is possible</p>
  
  <p>The latter requirement seems the achilles heel for Spring Security ACLs (their method seems likely to incur multiple DB hits for each document I manage)</p>
  
  <p>Anyone know of another ACL implementation? </p>
  
  <p>Thanks!</p>