Lukasz Lenart created WW-5724:
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Summary: Cached MessageFormat instances in
AbstractLocalizedTextProvider are shared between concurrent callers
Key: WW-5724
URL: https://issues.apache.org/jira/browse/WW-5724
Project: Struts 2
Issue Type: Bug
Reporter: Lukasz Lenart
Fix For: 7.4.0, 6.12.0
h2. Summary
{{AbstractLocalizedTextProvider}} caches {{java.text.MessageFormat}} instances
keyed by pattern and locale and returns the cached instance from
{{buildMessageFormat}}, while {{DefaultTextProvider}} builds a fresh instance
per call. {{MessageFormat}} is not thread-safe, so callers rendering the same
message concurrently format through one shared instance.
h2. Current behaviour
{{buildMessageFormat}} returns the cached instance on a hit and
{{formatWithNullDetection}} calls {{format()}} on it directly. The provider is
a singleton bean, so the cache and every instance in it are shared
application-wide. The sibling {{DefaultTextProvider.getText}} constructs a new
{{MessageFormat}} on each call.
A pattern carrying a date or time sub-format delegates to a
{{SimpleDateFormat}} held by the {{MessageFormat}}, which keeps per-call state
in its {{Calendar}}; concurrent {{format()}} calls on the shared instance can
render the wrong argument or throw. Number and choice sub-formats and plain
placeholders are not affected on current JDKs.
h2. Proposed change
Keep the cache, but have {{buildMessageFormat}} return a clone of the cached
instance, so the cached entry is only ever a template and is never formatted
directly. {{MessageFormat.clone()}} deep-copies its sub-formats. This preserves
the pattern-parsing cache the WW-5540 work relies on; measured against a fresh
instance per call and against synchronizing on the shared instance, cloning is
the cheapest of the three.
h2. Compatibility notes
No configuration or API change. Descendant classes that override
{{buildMessageFormat}} keep their current behaviour; only the base
implementation changes.
Applies to both maintenance lines.
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