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Date: Thu, 11 Feb 2010 08:22:28 +0000 (UTC)
From: "Henri Biestro (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Subject: [jira] Updated: (JEXL-97) JEXL parses long expressions with lots of
 parenthesis slowly
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     [ https://issues.apache.org/jira/browse/JEXL-97?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Henri Biestro updated JEXL-97:
------------------------------

    Affects Version/s:     (was: 2.0)
                           (was: 1.0)
        Fix Version/s: 2.0

Per previous tests, pb shows up in JEXL1.x but is fixed in JEXL 2.x.

> JEXL parses long expressions with lots of parenthesis slowly
> ------------------------------------------------------------
>
>                 Key: JEXL-97
>                 URL: https://issues.apache.org/jira/browse/JEXL-97
>             Project: Commons JEXL
>          Issue Type: Bug
>    Affects Versions: 1.1
>         Environment: Java
>            Reporter: Jeff Ichnowski
>            Priority: Minor
>             Fix For: 2.0
>
>         Attachments: proposed.patch
>
>
> JEXL's parser uses an unbounded JavaCC LOOKAHEAD to distinguish assignment expressions from other expressions.  The result is certain expressions take exponential time to parse.  The example snippet below demonstrates the problem.  On my machine parsing the expression below takes ~120 seconds.  Changing the parser to remove the LOOKAHEAD can get this to parse in milliseconds.  The lookahead appears to be in all versions of the parser source.
> import org.apache.commons.jexl.Expression;
> import org.apache.commons.jexl.ExpressionFactory;
> public class SlowParse {
>     public static void main(String[] args) throws Exception {
>         String input = 
>             "(((((((((((((((((((((((((z+y)/x)*w)-v)*u)/t)-s)*r)/q)+p)-o)*n)-m)+l)*k)+j)/i)+h)*g)+f)/e)+d)-c)/b)+a)";
>         // Make sure everything is loaded...
>         Expression expr = ExpressionFactory.createExpression(input);
>         long start = System.nanoTime();
>         expr = ExpressionFactory.createExpression(input);
>         long end = System.nanoTime();
>         System.out.printf("Parse took %.1f seconds\n", (end-start)/1e+9);
>     }
> }

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