public void visitLocationStep(LocationStep locationStep) {
super.visitLocationStep(locationStep);
boolean optimize = false;
// only location steps with predicates can be optimized:
if (locationStep.hasPredicates()) {
List preds = locationStep.getPredicates();
// walk through the predicates attached to the current location step.
// try to find a predicate containing an expression which is an instance
// of Optimizable.
for (Iterator i = preds.iterator(); i.hasNext(); ) {
Predicate pred = (Predicate) i.next();
FindOptimizable find = new FindOptimizable();
pred.accept(find);
List list = find.getOptimizables();
if (list.size() > 0 && canOptimize(list)) {
optimize = true;
break;
}
}
}
if (optimize) {
// we found at least one Optimizable. Rewrite the whole expression and
// enclose it in an (#exist:optimize#) pragma.
Expression parent = locationStep.getParent();
if (!(parent instanceof PathExpr)) {
LOG.warn("Parent expression of step is not a PathExpr: " + parent);
return;
}
if (LOG.isTraceEnabled())
LOG.trace("Rewriting expression: " + ExpressionDumper.dump(locationStep));
hasOptimized = true;
PathExpr path = (PathExpr) parent;
try {
// Create the pragma
ExtensionExpression extension = new ExtensionExpression(context);
extension.addPragma(new Optimize(context, Optimize.OPTIMIZE_PRAGMA, null, false));
extension.setExpression(locationStep);
// Replace the old expression with the pragma
path.replaceExpression(locationStep, extension);
} catch (XPathException e) {
LOG.warn("Failed to optimize expression: " + locationStep + ": " + e.getMessage(), e);
}
}
}
public void visitPredicate(Predicate predicate) {
++predicates;
super.visitPredicate(predicate);
--predicates;
}
