fix(sheet): isolate column width cache per sheet holder

fesod-sheet/src/main/java/org/apache/fesod/sheet/write/metadata/holder/WriteSheetHolder.java

@@ -47,7 +47,7 @@
  */
 @Getter
 @Setter
-@EqualsAndHashCode(exclude = {"parentWriteWorkbookHolder", "hasBeenInitializedTable"})
+@EqualsAndHashCode(exclude = {"parentWriteWorkbookHolder", "hasBeenInitializedTable", "columnWidthCache"})
 @NoArgsConstructor
 public class WriteSheetHolder extends AbstractWriteHolder {
     /**
@@ -88,6 +88,11 @@ public class WriteSheetHolder extends AbstractWriteHolder {
      */
     private Map<Integer, WriteTableHolder> hasBeenInitializedTable;
 
+    /***
+     * Per-sheet-holder cache of maximum column widths, keyed by column index.
+     */
+    private Map<Integer, Integer> columnWidthCache;
+
     /**
      * last column type
      *

fesod-sheet/src/main/java/org/apache/fesod/sheet/write/style/column/LongestMatchColumnWidthStyleStrategy.java

@@ -29,7 +29,6 @@
 import java.util.List;
 import java.util.Map;
 import org.apache.commons.collections4.CollectionUtils;
-import org.apache.fesod.common.util.MapUtils;
 import org.apache.fesod.sheet.enums.CellDataTypeEnum;
 import org.apache.fesod.sheet.metadata.Head;
 import org.apache.fesod.sheet.metadata.data.WriteCellData;
@@ -48,8 +47,6 @@ public class LongestMatchColumnWidthStyleStrategy extends AbstractColumnWidthSty
 
     private static final int MAX_COLUMN_WIDTH = 255;
 
-    private final Map<Integer, Map<Integer, Integer>> cache = MapUtils.newHashMapWithExpectedSize(8);
-
     @Override
     protected void setColumnWidth(
             WriteSheetHolder writeSheetHolder,
@@ -62,8 +59,11 @@ protected void setColumnWidth(
         if (!needSetWidth) {
             return;
         }
-        Map<Integer, Integer> maxColumnWidthMap =
-                cache.computeIfAbsent(writeSheetHolder.getSheetNo(), key -> new HashMap<>(16));
+        Map<Integer, Integer> maxColumnWidthMap = writeSheetHolder.getColumnWidthCache();
+        if (maxColumnWidthMap == null) {
+            maxColumnWidthMap = new HashMap<>(16);
+            writeSheetHolder.setColumnWidthCache(maxColumnWidthMap);
+        }
         Integer columnWidth = dataLength(cellDataList, cell, isHead);
         if (columnWidth < 0) {
             return;

fesod-sheet/src/test/java/org/apache/fesod/sheet/write/style/column/LongestMatchColumnWidthStyleStrategyTest.java

@@ -0,0 +1,92 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.fesod.sheet.write.style.column;
+
+import java.io.File;
+import java.nio.file.Path;
+import java.util.Collections;
+import org.apache.fesod.sheet.FesodSheet;
+import org.apache.fesod.sheet.testkit.Tags;
+import org.apache.poi.ss.usermodel.Sheet;
+import org.apache.poi.ss.usermodel.Workbook;
+import org.apache.poi.ss.usermodel.WorkbookFactory;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/**
+ * Regression tests for the per-sheet-holder width cache of {@link LongestMatchColumnWidthStyleStrategy}.
+ */
+@Tag(Tags.WRITE)
+class LongestMatchColumnWidthStyleStrategyTest {
+
+    private static final String LONG_VALUE = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
+
+    /**
+     * Control: when every writer gets its own strategy instance, both files get their own width.
+     */
+    @Test
+    void separateStrategyInstancesComputeEachWorkbookWidth(@TempDir Path dir) throws Exception {
+        File first = dir.resolve("separate-first.xlsx").toFile();
+        File second = dir.resolve("separate-second.xlsx").toFile();
+
+        write(first, LONG_VALUE, new LongestMatchColumnWidthStyleStrategy());
+        write(second, "A", new LongestMatchColumnWidthStyleStrategy());
+
+        Assertions.assertEquals(LONG_VALUE.length() * 256, columnWidth(first, 0));
+        Assertions.assertEquals(1 * 256, columnWidth(second, 0));
+    }
+
+    /**
+     * The width cache is keyed only by sheet number and is never cleared when a workbook finishes, so a strategy
+     * instance reused for a second writer keeps the first workbook's maximum. As a result the second workbook's
+     * column width is never set and stays at POI's default instead of the computed 1 * 256.
+     */
+    @Test
+    void sharedStrategyInstanceDoesNotLeakWidthAcrossWorkbooks(@TempDir Path dir) throws Exception {
+        File first = dir.resolve("shared-first.xlsx").toFile();
+        File second = dir.resolve("shared-second.xlsx").toFile();
+
+        LongestMatchColumnWidthStyleStrategy shared = new LongestMatchColumnWidthStyleStrategy();
+        write(first, LONG_VALUE, shared);
+        write(second, "A", shared);
+
+        Assertions.assertEquals(LONG_VALUE.length() * 256, columnWidth(first, 0));
+        Assertions.assertEquals(
+                1 * 256,
+                columnWidth(second, 0),
+                "column width leaked from the previous workbook when the strategy instance was reused");
+    }
+
+    private static void write(File file, String value, LongestMatchColumnWidthStyleStrategy strategy) {
+        FesodSheet.write(file)
+                .registerWriteHandler(strategy)
+                .sheet()
+                .doWrite(Collections.singletonList(Collections.singletonList(value)));
+    }
+
+    private static int columnWidth(File file, int column) throws Exception {
+        try (Workbook workbook = WorkbookFactory.create(file)) {
+            Sheet sheet = workbook.getSheetAt(0);
+            return sheet.getColumnWidth(column);
+        }
+    }
+}