Workbook getsheetname logs a warning for exceeding 31 characters

poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java

@@ -1213,11 +1213,29 @@ public String getPrintArea(int sheetIndex) {
      * If there are multiple matches, the first sheet from the list
      * of sheets is returned.
      *
+     * <p>
+     * Note that Excel and the underlying Apache POI library limit sheet names
+     * to **31 characters**. This method will throw an exception if the
+     * provided {@code name} is longer than 31 characters, as such a sheet
+     * cannot exist in a valid Excel workbook.
+     * </p>
+     *
      * @param name of the sheet
      * @return XSSFSheet with the name provided or {@code null} if it does not exist
+     * @throws IllegalArgumentException if the sheet name is longer than 31 characters
      */
     @Override
     public XSSFSheet getSheet(String name) {
+
+        if (name == null || name.isEmpty()) {
+            return null;
+        }
+
+        if(name.length() > MAX_SENSITIVE_SHEET_NAME_LEN) {
+            throw new IllegalArgumentException("Sheet name must not be longer than " +
+                    MAX_SENSITIVE_SHEET_NAME_LEN + " characters. Otherwise it cannot exist in Excel.");
+        }
+
         for (XSSFSheet sheet : sheets) {
             if (name.equalsIgnoreCase(sheet.getSheetName())) {
                 return sheet;

poi-ooxml/src/test/java/org/apache/poi/xssf/usermodel/TestXSSFWorkbook.java

@@ -1245,6 +1245,26 @@ void testRightToLeft() throws IOException {
         }
     }
 
+    /**
+     * Getting a sheet by name that exceeds 31 characters should throw
+     * an IllegalArgumentException
+     */
+    @Test
+    void testGetSheetWithNameExceeding31Characters() throws IOException {
+        try (XSSFWorkbook wb = new XSSFWorkbook()) {
+
+            // Attempting to GET a sheet with a name > 31 chars should throw
+            String sheetName = "ThisIsAVeryLongSheetNameExceeding31Chars";
+            IllegalArgumentException exception = assertThrows(
+                    IllegalArgumentException.class,
+                    () -> wb.getSheet(sheetName),
+                    "getSheet() should reject names longer than 31 characters"
+            );
+
+            assertTrue(exception.getMessage().contains("31 characters"));
+        }
+    }
+
     @Test
     void test501RC1Failure() throws Exception {
         String filename = "0-www-crossref-org.lib.rivier.edu_education-files_suffix-generator.xlsm";

poi/src/main/java/org/apache/poi/hssf/usermodel/HSSFWorkbook.java

@@ -1061,11 +1061,29 @@ public HSSFSheet getSheetAt(int index) {
      * If there are multiple matches, the first sheet from the list
      * of sheets is returned.
      *
+     * <p>
+     * Note that Excel and the underlying Apache POI library limit sheet names
+     * to **31 characters**. This method will throw an exception if the
+     * provided {@code name} is longer than 31 characters, as such a sheet
+     * cannot exist in a valid Excel workbook.
+     * </p>
+     *
      * @param name of the sheet
      * @return HSSFSheet with the name provided or {@code null} if it does not exist
+     * @throws IllegalArgumentException if the sheet name is longer than 31 characters
      */
     @Override
     public HSSFSheet getSheet(String name) {
+
+        if (name == null || name.isEmpty()) {
+            return null;
+        }
+
+        if(name.length() > MAX_SENSITIVE_SHEET_NAME_LEN) {
+            throw new IllegalArgumentException("Sheet name must not be longer than " +
+                    MAX_SENSITIVE_SHEET_NAME_LEN + " characters. Otherwise it cannot exist in Excel.");
+        }
+
         for (int k = 0; k < _sheets.size(); k++) {
             String sheetname = workbook.getSheetName(k);
 

poi/src/test/java/org/apache/poi/hssf/usermodel/TestHSSFWorkbook.java

@@ -395,6 +395,26 @@ void sheetSerializeSizeMismatch_bug45066() throws IOException {
         }
     }
 
+    /**
+     * Getting a sheet by name that exceeds 31 characters should throw
+     * an IllegalArgumentException
+     */
+    @Test
+    void testGetSheetWithNameExceeding31Characters() throws IOException {
+        try (HSSFWorkbook wb = new HSSFWorkbook()) {
+
+            // Attempting to GET a sheet with a name > 31 chars should throw
+            String sheetName = "ThisIsAVeryLongSheetNameExceeding31Chars";
+            IllegalArgumentException exception = assertThrows(
+                    IllegalArgumentException.class,
+                    () -> wb.getSheet(sheetName),
+                    "getSheet() should reject names longer than 31 characters"
+            );
+
+            assertTrue(exception.getMessage().contains("31 characters"));
+        }
+    }
+
     /**
      * Checks that us and HSSFName play nicely with named ranges
      *  that point to deleted sheets