[jira] [Created] (VELOCITY-917) VTL Grammar Characters Configuration

["Claude Brisson (JIRA)" <ji...@apache.org>]

Claude Brisson created VELOCITY-917:
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             Summary: VTL Grammar Characters Configuration
                 Key: VELOCITY-917
                 URL: https://issues.apache.org/jira/browse/VELOCITY-917
             Project: Velocity
          Issue Type: New Feature
          Components: Engine
    Affects Versions: 2.2
            Reporter: Claude Brisson
            Assignee: Claude Brisson


Experimental feature.

The goal is to introduce new configuration parameters to be able to change the VTL grammar. For instance:

parser.character.dollar = '~'
parser.character.hash = '@'
parser.character.arobase = '%'
parser.character.star = '?'

Requirements:

+ fully B.C.
+ done at runtime, without the need to recompile the parser
+ null impact on performance

Implementation:

1. Parametrize code that needs explicit references to those characters
2. Define a ParserTokenManager interface and have the parser use this interface rather than a concrete class
3. Use a custom class loader to *patch* the concrete token manager .class file, instantiate this custom token manager and initialize parsers with it

The binary patch is prepared at compilation time (there will be one patch per JRE vendor and class file version).

Due to the limited capability of this technique, the chosen characters are restricted to UTF-8 single bytes characters. Patches _could_ be prepared for two-bytes or more characters, but there would be the need to have as many parser objects as variants in one/two/... characters combinations.

Also, some characters and combinations are obviously invalid.




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