[CLK-306] Replacing OGNL with MVEL

• Type: New Feature
• Status: In Progress
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.4
• Fix Version/s: 2.4.0-RC1
• Component/s: core
• Environment: Target Click 1.5
• Assignee: Malcolm Edgar
• Reporter: Bob Schellink
• Created: 07/Feb/08 04:46
• Updated: 18/Oct/13 20:18

Description

I have been following both OGNL and MVEL (another expression language) development the last couple of months. If we are going to make changes to this here are some things you might find interesting:

• OGNL 2.7.1 which is included in tapestry 4.1, now sports byte code enhancement. This was added by one of the tapestry authors to make OGNL much faster than its reflection mode. However in my testing 2.7.1 threw exceptions every now and then. So still buggy.

• MVEL (http://mvel.codehaus.org/) seems like a good replacement for OGNL. It has good docs and is actively developed. They even fixed a bug I logged! Like OGNL, MVEL also runs in two modes, either reflection or byte compiled. Unlike OGNL, MVEL's reflection mode is faster than Click's reflection mode.

I am no expert on this but according to the article below (from MVEL's author), byte code enhancement have some problems in that generated classes accumulate in java's perm space and will only be removed when their classloader is removed.
http://artexpressive.blogspot.com/2007/07/mvel-by-numbers-real-story.html

So MVEL in reflection mode looks like an ideal solution here. The power of OGNL with the performance of Click reflection.

Table columns can again take advantage of expressions. For example to aggregate a total for the row -> new Column("price * tax");