On 17/05/2021 21:42, Rémy Maucherat wrote:
On Mon, May 17, 2021 at 8:47 PM Mark Thomas <ma...@apache.org> wrote:
Hi all,
I am looking at some of the optimizations requested in [1]
One of the examples is show below. Code like this is used when the JSP
calls a tag.
private boolean _jspx_meth_mytag_005fhelloWorld_005f0(
jakarta.servlet.jsp.PageContext _jspx_page_context)
throws java.lang.Throwable {
jakarta.servlet.jsp.PageContext pageContext = _jspx_page_context;
// mytag:helloWorld
....
}
The question is, can the generated code above be changed to something
like this:
private boolean _jspx_meth_mytag_005fhelloWorld_005f0(
final jakarta.servlet.jsp.PageContext pageContext)
throws java.lang.Throwable {
// mytag:helloWorld
....
}
I am assuming that the aliasing of _jspx_page_context to pageContext is
so that _jspx_page_context always references the original even if the
tag decides to do something like:
pageContext = new MyCustomPageContextImpl();
The question is, is behaviour like this allowed?
I can't see anything in the spec that disallows this.
I don't think the aliasing is a defence against malicious apps as it is
only the implicit objects that are protected this way. Internal objects
(those name _jsp*) are unprotected.
Given that the original authors (who were on the JSP EG at the time)
added this aliasing for the implicit objects, it looks like the
intention was to allow applications to manipulate/replace the implicit
objects if they wish - without breaking Jasper.
If the above assumptions are correct, what do we want to do about [1]?
The aliasing is often unnecessary but will sometimes be essential. Do we
reject this optimization request? Do we add a configuration option? Do
we try and make this aspect of the code generation pluggable somehow?
Something else?
Thoughts very welcome.
Well, although I do see how this makes the generated code a little bit
smaller, this is a rather small optimization (even with 1000s of
occurrences). Since you've identified a risk, and it seems correct to me
(I'm almost certain this was on purpose and because the idea is not
forbidden in the specification), I would say we should skip that one.
That works for me.
_jspx_page_context is referenced in multiple places in Generator. I
can't see a way to make that configurable that isn't relatively invasive
/ risky for the benefit it brings.
If the EG were to declare that implicit variables should be declared as
final then that would change things - but I don't see that happening.
Mark
[1] https://bz.apache.org/bugzilla/show_bug.cgi?id=65124
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