fix: support immutable lists in dynamic header

fesod/src/main/java/org/apache/fesod/excel/metadata/AbstractParameterBuilder.java

@@ -19,9 +19,11 @@
 
 package org.apache.fesod.excel.metadata;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
 import java.util.Objects;
+import java.util.stream.Collectors;
 import org.apache.fesod.excel.converters.Converter;
 import org.apache.fesod.excel.enums.CacheLocationEnum;
 import org.apache.fesod.excel.util.ListUtils;
@@ -39,10 +41,23 @@ public abstract class AbstractParameterBuilder<T extends AbstractParameterBuilde
      * @return
      */
     public T head(List<List<String>> head) {
-        parameter().setHead(head);
+        parameter().setHead(toMutableListIfNecessary(head));
         return self();
     }
 
+    /**
+     * Ensures and returns a fully mutable deep copy of head list.
+     *
+     * @param head head The source list to create a mutable copy from.
+     * @return A new, fully mutable deep copy, or the original list if the input is null or empty.
+     */
+    private List<List<String>> toMutableListIfNecessary(List<List<String>> head) {
+        if (null == head || head.isEmpty()) {
+            return head;
+        }
+        return head.stream().map(ArrayList::new).collect(Collectors.toList());
+    }
+
     /**
      * You can only choose one of the {@link #head(List)} and {@link #head(Class)}
      *

fesod/src/test/java/org/apache/fesod/excel/head/ImmutableListHeadDataListener.java

@@ -0,0 +1,64 @@
+/*
+ * 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.excel.head;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import org.apache.fesod.excel.context.AnalysisContext;
+import org.apache.fesod.excel.metadata.data.ReadCellData;
+import org.apache.fesod.excel.read.listener.ReadListener;
+import org.junit.jupiter.api.Assertions;
+
+public class ImmutableListHeadDataListener implements ReadListener<Map<Integer, String>> {
+
+    private List<Map<Integer, String>> list = new ArrayList<Map<Integer, String>>();
+
+    @Override
+    public void invokeHead(Map<Integer, ReadCellData<?>> headMap, AnalysisContext context) {
+        Assertions.assertNotNull(context.readRowHolder().getRowIndex());
+        headMap.forEach((key, value) -> {
+            Assertions.assertEquals(value.getRowIndex(), context.readRowHolder().getRowIndex());
+            Assertions.assertEquals(value.getColumnIndex(), key);
+        });
+    }
+
+    @Override
+    public void invoke(Map<Integer, String> data, AnalysisContext context) {
+        list.add(data);
+    }
+
+    @Override
+    public void doAfterAllAnalysed(AnalysisContext context) {
+        List<List<String>> head = context.readSheetHolder().getHead();
+
+        Assertions.assertInstanceOf(ArrayList.class, head);
+        for (List<String> item : head) {
+            Assertions.assertInstanceOf(ArrayList.class, item);
+        }
+
+        Assertions.assertEquals(1, list.size());
+        Map<Integer, String> data = list.get(0);
+        Assertions.assertEquals("stringData", data.get(0));
+        Assertions.assertEquals("1", data.get(1));
+        Assertions.assertEquals("2025-10-31 01:01:01", data.get(2));
+        Assertions.assertEquals("extraData", data.get(3));
+    }
+}

fesod/src/test/java/org/apache/fesod/excel/head/ImmutableListHeadDataTest.java

@@ -0,0 +1,102 @@
+/*
+ * 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.excel.head;
+
+import java.io.File;
+import java.text.ParseException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import org.apache.fesod.excel.FastExcel;
+import org.apache.fesod.excel.util.DateUtils;
+import org.apache.fesod.excel.util.TestFileUtil;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.MethodOrderer;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestMethodOrder;
+
+@TestMethodOrder(MethodOrderer.MethodName.class)
+public class ImmutableListHeadDataTest {
+
+    private static File file07;
+    private static File file03;
+    private static File fileCsv;
+
+    @BeforeAll
+    public static void init() {
+        file07 = TestFileUtil.createNewFile("listHead07.xlsx");
+        file03 = TestFileUtil.createNewFile("listHead03.xls");
+        fileCsv = TestFileUtil.createNewFile("listHeadCsv.csv");
+    }
+
+    @Test
+    public void t01ReadAndWrite07() throws Exception {
+        readAndWrite(file07);
+    }
+
+    @Test
+    public void t02ReadAndWrite03() throws Exception {
+        readAndWrite(file03);
+    }
+
+    @Test
+    public void t03ReadAndWriteCsv() throws Exception {
+        readAndWrite(fileCsv);
+    }
+
+    private void readAndWrite(File file) throws Exception {
+        FastExcel.write(file)
+                .head(head())
+                .registerWriteHandler(new ImmutableListHeadDataWriteHandler())
+                .sheet()
+                .doWrite(data());
+
+        FastExcel.read(file)
+                .head(head())
+                .registerReadListener(new ImmutableListHeadDataListener())
+                .sheet()
+                .doRead();
+    }
+
+    private List<List<String>> head() {
+        List<List<String>> list = new ArrayList<List<String>>();
+        List<String> head0 = Arrays.asList("stringTitle");
+        List<String> head1 = new ArrayList<String>();
+        head1.add("numberTitle1");
+        head1.add("numberTitle2");
+
+        list.add(head0);
+        list.add(Collections.unmodifiableList(head1));
+        list.add(Collections.singletonList("datetimeTitle"));
+        return list;
+    }
+
+    private List<List<Object>> data() throws ParseException {
+        List<List<Object>> list = new ArrayList<List<Object>>();
+        List<Object> data0 = new ArrayList<Object>();
+        data0.add("stringData");
+        data0.add(1);
+        data0.add(DateUtils.parseDate("2025-10-31 01:01:01"));
+        data0.add("extraData");
+        list.add(data0);
+        return list;
+    }
+}

fesod/src/test/java/org/apache/fesod/excel/head/ImmutableListHeadDataWriteHandler.java

@@ -0,0 +1,39 @@
+/*
+ * 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.excel.head;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.apache.fesod.excel.write.handler.SheetWriteHandler;
+import org.apache.fesod.excel.write.handler.context.SheetWriteHandlerContext;
+import org.junit.jupiter.api.Assertions;
+
+public class ImmutableListHeadDataWriteHandler implements SheetWriteHandler {
+
+    @Override
+    public void afterSheetDispose(SheetWriteHandlerContext context) {
+        List<List<String>> head = context.getWriteContext().writeSheetHolder().getHead();
+
+        Assertions.assertInstanceOf(ArrayList.class, head);
+        for (List<String> item : head) {
+            Assertions.assertInstanceOf(ArrayList.class, item);
+        }
+    }
+}