从你的图片来看，源工作表似乎已经将显示网格线设置为false。这存储在XSSFSheet的CTWorksheet的工作表视图设置中。因此，如果复制的工作表也应该有这样的设置，那么CTWorksheet的工作表视图设置也需要复制。为此，请执行以下操作：

...
sheetTo.getCTWorksheet().setSheetViews(sheetFrom.getCTWorksheet().getSheetViews());
...

但是sheetViews也存储了关于所选工作表的设置，因此将sheetTo的selected设置为false，否则结果工作簿中将选择多个工作表

...
sheetTo.setSelected(false); 
...

但是，您可能会遇到代码lne的其他问题：

...
XSSFSheet sheetTo = (XSSFSheet) workbookTo..createSheet(workbookFrom.getSheetAt(sheetIndex).getSheetName());
...

如果多个workbookFrom工作簿的工作表具有相同的工作表名称，该怎么办？然后这一行将抛出java.lang.IllegalArgumentException，因为workbookTo工作簿已经包含一个具有此名称的工作表。因此，需要考虑来自多个workbookFrom的工作表可能具有相同的名称。如果是，则将（n）（其中n是计数器编号）附加到名称，以使其在结果工作簿中唯一。
完整的示例为Minimal, Reproducible Example：

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;

import java.io.*;
import java.util.*;

class ExcelMergeFiles {
    
    private void mergeExcelFiles(String excelFilesPath, List<String> files) {
        Workbook workbookTo;
        Workbook workbookFrom;   
        try {
            File f1 = new File(files.get(0));
            workbookTo = WorkbookFactory.create(new FileInputStream(f1)); // workbook that will be the result
            files.remove(0); // first file is workbookTo and not needs to be merged into the result
            for (String file : files) {
                File f = new File(file);
                workbookFrom = WorkbookFactory.create(new FileInputStream(f)); // workbook that needs to be merged into the result
                for (int sheetIndex = 0; sheetIndex < workbookFrom.getNumberOfSheets(); sheetIndex++) {
                    // get sheetFrom
                    XSSFSheet sheetFrom = (XSSFSheet) workbookFrom.getSheetAt(sheetIndex);
                    
                    //consider that sheets from multiple workbookFrom could have the same name, if so, then append (n)
                    int n = 1;
                    String sheetName = sheetFrom.getSheetName();
                    while (workbookTo.getSheet(sheetName) != null) {
                        if (sheetName.matches("^.*? \\(\\d*\\)$")) {
                            sheetName = sheetName.replaceAll(" \\(\\d*\\)", " ("+ ++n +")");
                        } else {
                            sheetName = sheetName + " ("+ ++n +")";
                        }
                    }
                    
                    // create sheetTo
                    XSSFSheet sheetTo = (XSSFSheet) workbookTo.createSheet(sheetName);
                    
                    //get last used column of sheetFrom
                    int lastRow = sheetFrom.getLastRowNum();
                    int lastCol = 0;
                    for (int i = 0; i < lastRow; i++) {
                        Row row = sheetFrom.getRow(i);
                        if (row != null) {
                            if (row.getLastCellNum() > lastCol) {
                                lastCol = row.getLastCellNum();
                            }
                        }
                    }

                    // copy used range from sheetFrom to sheetTo
                    CellRangeAddress cellAddresses = new CellRangeAddress(0, lastRow, 0, lastCol);
                    XSSFRangeCopier xssfRangeCopier = new XSSFRangeCopier(sheetFrom, sheetTo);
                    xssfRangeCopier.copyRange(cellAddresses, cellAddresses, true, true);
                    
                    // copy the column widths from sheetFrom to sheetTo
                    for (int j = 0; j < lastCol; j++) {
                        sheetTo.setColumnWidth(j, sheetFrom.getColumnWidth(j));
                    }
                    
                    // copy default row height from sheetFrom to sheetTo
                    sheetTo.setDefaultRowHeight(sheetFrom.getDefaultRowHeight());
                    
                    // copy row heights from sheetFrom to sheetTo
                    for (int i = 0; i < lastRow; i++) {
                        Row rowFrom = sheetFrom.getRow(i);
                        Row rowTo = sheetTo.getRow(i);
                        if (rowFrom != null && rowTo != null) {
                            rowTo.setHeight(rowFrom.getHeight());
                        }
                    }

                    // copy the sheetViews which stores the setting about visibility of grid lines for example
                    sheetTo.getCTWorksheet().setSheetViews(sheetFrom.getCTWorksheet().getSheetViews());
                    // sheetViews also stores the setting about selected sheets, so set selected of sheetTo false, else multiple sheets will be selected in result workbook
                    sheetTo.setSelected(false);
                    
                    // close workbookFrom
                    workbookFrom.close();
                    
                    f.delete();
                    
                }
                
            }
            // write the workbookTo as the result.xlsx
            FileOutputStream out = new FileOutputStream(new File(excelFilesPath + "/" + "result" + ".xlsx"));
            workbookTo.write(out);
            out.close();
            workbookTo.close();
            f1.delete();

        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    public static void main(String[] args) throws Exception {
        List<String> files = new ArrayList<String>();
        files.add("./ExcelFiles/a.xlsx");
        files.add("./ExcelFiles/b.xlsx");
        files.add("./ExcelFiles/c.xlsx");
        ExcelMergeFiles app = new ExcelMergeFiles();
        app.mergeExcelFiles("./ExcelFiles", files);
    }
}

在目录./ExcelFiles中期望文件a.xlsx、b.xlsx、c.xlsx，并将表单b.xlsx和c.xlsx合并到a.xlsx中，并将结果存储为result.xlsx。