JEXL parses long expressions with lots of parenthesis slowly
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Key: JEXL-97
URL: https://issues.apache.org/jira/browse/JEXL-97
Project: Commons JEXL
Issue Type: Bug
Affects Versions: 1.0, 1.1, 2.0
Environment: Java
Reporter: Jeff Ichnowski
Priority: Minor
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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