fix: handle escaped closing brace in template placeholder parsing

When a template placeholder contains an escaped closing brace like {foo\},
the parser would throw StringIndexOutOfBoundsException because it attempted
to use suffixIndex=-1 in a substring operation.

Added a bounds check after the inner while loop to break out when no valid
(non-escaped) closing brace is found.

Author: roeniss

fesod-examples/fesod-sheet-examples/src/test/java/org/apache/fesod/sheet/temp/issue462/EscapedPlaceholderTest.java

@@ -0,0 +1,178 @@
+/*
+ * 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.temp.issue462;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.fesod.sheet.FesodSheet;
+import org.apache.fesod.sheet.util.TestFileUtil;
+import org.apache.poi.ss.usermodel.Cell;
+import org.apache.poi.ss.usermodel.Row;
+import org.apache.poi.ss.usermodel.Sheet;
+import org.apache.poi.ss.usermodel.Workbook;
+import org.apache.poi.xssf.usermodel.XSSFWorkbook;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test case for issue #462: ArrayIndexOutOfBoundsException when placeholder content is '{foo\}'
+ *
+ * When a placeholder has an escaped closing brace like {foo\}, the parser should handle it
+ * gracefully without throwing an exception.
+ */
+public class EscapedPlaceholderTest {
+
+    private static final String TEMPLATE_PATH = TestFileUtil.getPath() + "temp/issue462" + File.separator;
+
+    @BeforeAll
+    public static void createTemplates() throws IOException {
+        // Create template with escaped placeholder {foo\}
+        createTemplate("escaped_suffix.xlsx", "{foo\\}");
+
+        // Create template with escaped prefix \{foo}
+        createTemplate("escaped_prefix.xlsx", "\\{foo}");
+
+        // Create template with normal placeholder for comparison
+        createTemplate("normal.xlsx", "{foo}");
+
+        // Create template with mixed content
+        createTemplate("mixed.xlsx", "prefix {foo\\} suffix");
+    }
+
+    private static void createTemplate(String fileName, String content) throws IOException {
+        File templateFile = new File(TEMPLATE_PATH + fileName);
+        try (Workbook workbook = new XSSFWorkbook();
+                FileOutputStream fos = new FileOutputStream(templateFile)) {
+            Sheet sheet = workbook.createSheet("Sheet1");
+            Row row = sheet.createRow(0);
+            Cell cell = row.createCell(0);
+            cell.setCellValue(content);
+            workbook.write(fos);
+        }
+    }
+
+    /**
+     * Test that template with {foo\} (escaped closing brace) does not throw exception.
+     * The escaped brace means there's no valid closing brace, so this should be treated as literal text.
+     */
+    @Test
+    public void testEscapedSuffixPlaceholder() {
+        String templateFileName = TEMPLATE_PATH + "escaped_suffix.xlsx";
+        String outputFileName = TEMPLATE_PATH + "output_escaped_suffix.xlsx";
+
+        Map<String, Object> data = new HashMap<>();
+        data.put("foo", "replaced_value");
+
+        // This should not throw an exception
+        Assertions.assertDoesNotThrow(() -> {
+            FesodSheet.write(new File(outputFileName))
+                    .withTemplate(new File(templateFileName))
+                    .sheet()
+                    .doFill(data);
+        });
+
+        // Verify output file exists and can be read
+        List<Object> result = FesodSheet.read(new File(outputFileName))
+                .sheet()
+                .headRowNumber(0)
+                .doReadSync();
+        Assertions.assertFalse(result.isEmpty());
+    }
+
+    /**
+     * Test that template with \{foo} (escaped opening brace) is treated as literal text.
+     */
+    @Test
+    public void testEscapedPrefixPlaceholder() {
+        String templateFileName = TEMPLATE_PATH + "escaped_prefix.xlsx";
+        String outputFileName = TEMPLATE_PATH + "output_escaped_prefix.xlsx";
+
+        Map<String, Object> data = new HashMap<>();
+        data.put("foo", "replaced_value");
+
+        // This should not throw an exception
+        Assertions.assertDoesNotThrow(() -> {
+            FesodSheet.write(new File(outputFileName))
+                    .withTemplate(new File(templateFileName))
+                    .sheet()
+                    .doFill(data);
+        });
+
+        // Verify the output
+        List<Object> result = FesodSheet.read(new File(outputFileName))
+                .sheet()
+                .headRowNumber(0)
+                .doReadSync();
+        Assertions.assertFalse(result.isEmpty());
+    }
+
+    /**
+     * Test that normal placeholder {foo} still works correctly.
+     */
+    @Test
+    public void testNormalPlaceholder() {
+        String templateFileName = TEMPLATE_PATH + "normal.xlsx";
+        String outputFileName = TEMPLATE_PATH + "output_normal.xlsx";
+
+        Map<String, Object> data = new HashMap<>();
+        data.put("foo", "replaced_value");
+
+        FesodSheet.write(new File(outputFileName))
+                .withTemplate(new File(templateFileName))
+                .sheet()
+                .doFill(data);
+
+        // Verify the placeholder was replaced
+        List<Object> result = FesodSheet.read(new File(outputFileName))
+                .sheet()
+                .headRowNumber(0)
+                .doReadSync();
+        Assertions.assertFalse(result.isEmpty());
+
+        @SuppressWarnings("unchecked")
+        Map<String, String> row = (Map<String, String>) result.get(0);
+        Assertions.assertEquals("replaced_value", row.get(0));
+    }
+
+    /**
+     * Test mixed content with escaped placeholder in the middle.
+     */
+    @Test
+    public void testMixedContentWithEscapedPlaceholder() {
+        String templateFileName = TEMPLATE_PATH + "mixed.xlsx";
+        String outputFileName = TEMPLATE_PATH + "output_mixed.xlsx";
+
+        Map<String, Object> data = new HashMap<>();
+        data.put("foo", "replaced_value");
+
+        // This should not throw an exception
+        Assertions.assertDoesNotThrow(() -> {
+            FesodSheet.write(new File(outputFileName))
+                    .withTemplate(new File(templateFileName))
+                    .sheet()
+                    .doFill(data);
+        });
+    }
+}

fesod-sheet/src/main/java/org/apache/fesod/sheet/write/executor/ExcelWriteFillExecutor.java

@@ -559,6 +559,9 @@ private String prepareData(
                     suffixIndex = -1;
                 }
             }
+            if (suffixIndex < 0) {
+                break out;
+            }
             if (analysisCell == null) {
                 analysisCell = initAnalysisCell(rowIndex, columnIndex);
             }