[yebuguntang]

Summary

fixes #1305

LongestMatchColumnWidthStyleStrategy cached the max column width in a field keyed only by sheetNo. When the same strategy instance was reused across two ExcelWriter instances (or two workbooks), both used sheetNo = 0, so the second workbook's widths could never beat the value cached from the first one. As a result Sheet.setColumnWidth was never called and the second workbook fell back to POI's default column width.

Fix

Move the per-column max-width cache from the strategy instance onto WriteSheetHolder (columnWidthCache). The strategy is now stateless with respect to width tracking, so:

• reusing one strategy across writers no longer leaks widths between workbooks/sheets;
• there is no shared mutable state, so the concurrency concerns raised in the issue (synchronized map vs. single-threaded access) become moot.

This follows the same per-holder isolation pattern used for converter state (e.g. #740), keeping related state co-located with the holder that owns it.

Test

Added LongestMatchColumnWidthStyleStrategyTest:

• separateStrategyInstancesComputeEachWorkbookWidth — control case (separate instances).
• sharedStrategyInstanceDoesNotLeakWidthAcrossWorkbooks — regression case that fails against the old cache-on-strategy implementation and passes after the fix.

Notes

The two design points discussed in #1305 (strong vs. weak references, thread safety) are no longer relevant because the cache is now per-holder and not shared.

[Mikkey-f]

Thanks @yebuguntang — I reproduced the leak and verified the fix locally (Windows 11, JDK 17).

Root cause: The strategy cache is keyed by sheetNo only, so two ExcelWriters both use key 0. Since a width is only applied when it beats the cached maximum, the second workbook's shorter value never reaches setColumnWidth and stays at POI's default.

Verification

• Red: with only the two product files reverted to current main (your tests kept), sharedStrategyInstanceDoesNotLeakWidthAcrossWorkbooks fails with expected: <256> but was: <2048>; the separate-instance control test still passes.
• Green: both tests pass (2/2).
• Full suite (mvn clean package -Dmaven.test.skip=false -pl fesod-common,fesod-shaded,fesod-sheet): 60 + 1,791 tests, 0 failures; spotless:check clean.

Code review: Moving the cache to WriteSheetHolder gives it the right owner — one map per sheet, lifetime tied to the workbook, and it still accumulates the running maximum across doWrite calls on the same sheet. Excluding it from @EqualsAndHashCode matches the existing hasBeenInitializedTable pattern. SimpleColumnWidthStyleStrategy and AbstractHeadColumnWidthStyleStrategy don't hold per-instance state, so there's no sibling copy of this bug.

Two nits (non-blocking)

1. WriteSheetHolder.columnWidthCache has no javadoc while the surrounding fields do — a one-liner would keep the holder self-documenting.
2. The new test class javadoc still says "per-instance width cache"; after the fix it's per sheet holder.

LGTM — correct state ownership and a deterministic regression test.

[yebuguntang]

Thank you @Mikkey-f for the careful review and for taking the time to reproduce the leak and verify the fix — it really helped.

I also overlooked the project's documentation conventions: the new field should have had a javadoc, and the test comment should have been updated along with the code. Lesson learned — I'll pay closer attention to javadoc and to keeping comments in sync in future contributions.

Thanks again for the guidance, much appreciated!

[Copilot]

🟢 Approval recommended

No active review issues block the change to isolate column-width tracking per sheet holder.

No open issues 🎉

What changed in this PR

Fixes #1305 by moving column-width tracking from the reusable strategy to each sheet holder, preventing cached widths from leaking across workbooks.

Changes:

• Adds a per-holder column-width cache, excluded from equality and hash-code calculations.
• Updates the strategy to lazily initialize and use the holder’s cache.
• Adds real-file tests covering separate strategy instances and one instance shared across writers.

File	Description
fesod-sheet/​src/​test/​java/​org/​apache/​fesod/​sheet/​write/​style/​column/​LongestMatchColumnWidthStyleStrategyTest.java	Adds control and regression tests that verify saved workbook widths.
fesod-sheet/​src/​main/​java/​org/​apache/​fesod/​sheet/​write/​style/​column/​LongestMatchColumnWidthStyleStrategy.java	Replaces strategy-owned width tracking with the sheet holder’s cache.
fesod-sheet/​src/​main/​java/​org/​apache/​fesod/​sheet/​write/​metadata/​holder/​WriteSheetHolder.java	Adds the isolated width cache and excludes it from equality and hashing.

_{Review effort: Balanced}