It's a simple Expression Language (EL) for Java, the code base sometime ago was migrated to the Apache commons ognl and this source code is used just to maintenance 3.x branch. The new version from Apache will start from 4.x

Out of incubator and now officially found here http://commons.apache.org/ognl/

OGNL stands for Object-Graph Navigation Language; it is an expression language for getting and setting properties of Java objects. You use the same expression for both getting and setting the value of a property.

The ognl.Ognl class contains convenience methods for evaluating OGNL expressions. You can do this in two stages, parsing an expression into an internal form and then using that internal form to either set or get the value of a property; or you can do it in a single stage, and get or set a property using the String form of the expression directly.

OGNL started out as a way to set up associations between UI components and controllers using property names. As the desire for more complicated associations grew, Drew Davidson created what he called KVCL, for Key-Value Coding Language, egged on by Luke Blanshard. Luke then reimplemented the language using ANTLR, came up with the new name, and, egged on by Drew, filled it out to its current state. Later on Luke again reimplemented the language using JavaCC. Further maintenance on all the code is done by Drew (with spiritual guidance from Luke).

We pronounce OGNL as a word, like the last syllables of a drunken pronunciation of "orthogonal."

• Language Guide
• Developer Guide
• Version Notes

• How to define an AccessMember?
  • the best way is to implement your own AccessMember which will suite your project best, you can base on existing DefaultAccessMember and adjust it to your needs. Since version 3.2.16 there is AbstractAccessMemeber which can be used a start point for your own implementation, see the example below:

       MemberAccess memberAccess = new AbstractMemberAccess() {
           @Override
           public boolean isAccessible(Map context, Object target, Member member, String propertyName) {
               int modifiers = member.getModifiers();
               return Modifier.isPublic(modifiers);
           }
       };
    

• How to run OGNL in Google AppEngine?
  • you need to tell OGNL to not do security manager permission checks, which will fail since GAE has a security manager and you don't have the ability to add the OGNL-specific permissions. Therefore, somewhere in your initialization code, add this OgnlRuntime.setSecurityManager(null);.