Dmitri Blinov created JEXL-228:
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Summary: Ability to read j.u.Collection elements other than
instanceof j.u.List by using [] and . operator
Key: JEXL-228
URL: https://issues.apache.org/jira/browse/JEXL-228
Project: Commons JEXL
Issue Type: Improvement
Affects Versions: 3.1
Reporter: Dmitri Blinov
Priority: Minor
In the current implementation of Jexl there is a possibility to address in a
script the specific elements of {{List}} and {{Array}} by using operators
{{[]}} or {{.}}, whereas its not that simple for descendants of {{Set}} or any
other {{Collection}} descendant, as there is no such an operator for them out
of the box. But in practice this is not so uncommon task for a script writer to
get, for example, the first element of the LinkedHashSet, which is supposed to
maintain the logical order of its elements, but unfortunately does not
implement {{List}} interface for us to be able to address its elements in that
order. I believe such a basic functionality - deserves to be available for
script witers from the start.
I have been experimenting with overloading access operators in customized
JexlArithmetic for a while and have managed to overload operators {{[]}} and
{{.}} so that they could be used not only for {{List}} interfaces but for other
{{Collection}} types as well:
{code}
protected Object nth(Collection c, int i) {
if (c instanceof List) {
List list = (List) c;
return list.get(i);
} else {
for (Object o : c) {
if (i-- == 0)
return o;
}
}
return null;
}
public Object propertyGet(Collection c, Number n) {
return nth(c, n.intValue());
}
public Object arrayGet(Collection c, Number n) {
return nth(c, n.intValue());
}
{code}
But I'm not satisfied with the fact that I have disabled alltogether the
initial Jexl implementation of access operators for {{LIst}} types.
The suggestion is to add the ability for Jexl scripts to read, not manipulate,
elements of any {{Collection}} type.
BTW, I have found that for {{List}} elements this solution is roughly 50%
faster compared with that of built-in Jexl List access implementation, so may
be there should be a place for a performance improvement in a way Jexl itself
accesses list elements.
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