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From "Robert Muir (JIRA)" <>
Subject [jira] [Commented] (LUCENE-6651) Remove private field reflection (setAccessible) in AttributeImpl#reflectWith
Date Wed, 01 Jul 2015 18:56:06 GMT


Robert Muir commented on LUCENE-6651:

I like the idea of the simple solution! I agree with you, it is better to be simple here.

> Remove private field reflection (setAccessible) in AttributeImpl#reflectWith
> ----------------------------------------------------------------------------
>                 Key: LUCENE-6651
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/other
>    Affects Versions: 5.2.1
>            Reporter: Uwe Schindler
>            Assignee: Uwe Schindler
>             Fix For: 5.3, Trunk
>         Attachments: LUCENE-6651-MethodHandles.patch
> In AttributeImpl we currently have a "default" implementation of reflectWith (which is
used by toString() and other methods) that uses reflection to list all private fields of the
implementation class and reports them to the AttributeReflector (used by Solr and Elasticsearch
to show analysis output).
> Unfortunately this default implementation needs to access private fields of a subclass,
which does not work without doing Field#setAccessible(true). And this is done without AccessController#doPrivileged()!
> There are 2 solutions to solve this:
> - Reimplement the whole thing with MethodHandles. MethodHandles allow to access private
fields, if you have a MethodHandles.Lookup object created from inside the subclass. The idea
is to add a protected constructor taking a Lookup object (must come from same class). This
Lookup object is then used to build methodHandles that can be executed to report the fields.
Backside: We have to require subclasses that want this "automatic" reflection to pass a Lookup
object in ctor's {{super(MethodHandles.lookup())}} call. This breaks backwards for implementors
of AttributeImpls
> - The second idea is to remove the whole reflectWith default impl and make the method
abstract. This would require a bit more work in tons of AttributeImpl classes, but you already
have to implement something like this for equals/hashCode, so its just listing all fields.
This would of couse break backwards, too. So my plan would be to implement the missing methods
everywhere (as if it were abstract), but keep the default implementation in 5.x. We just would
do AccessController.doPrivileged().

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