Java Apache Poi,如何同时设置背景颜色和边框

我试图生成一个excel表,其中包含带边框的Mutiplication Table并设置背景颜色,但仅适用于第1列和第1行.

这是一个正确的例子：correct example

我写了类似的东西,但在结果文件中,彩色单元格没有边框:(.

请解释我如何同时设置背景颜色和边框.

import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.hssf.usermodel.hssfWorkbook;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.IndexedColors;

import java.awt.image.IndexColorModel;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;

public class Excel {
    public static void main(String[] args) throws IOException {

        Scanner in = new Scanner(system.in);

        System.out.println("enter number of rows: ");
        int x = in.nextInt();
        System.out.println("enter number of columns: ");
        int y = in.nextInt();
        System.out.println("enter name of file: ");
        String fileName = in.next() + ".xls";

        System.out.println("Multiplication table will be created in file: " + fileName);

        createExcelMultiplicationTable(fileName,x,y);

        System.out.println("Process successful executed");
    }

    private static void createExcelMultiplicationTable(String fileName,int x,int y) throws IOException {
        Workbook workbook = new hssfWorkbook();
        Sheet sheet = workbook.createSheet("multiplicationTable");

        CellStyle backgroundStyle = workbook.createCellStyle();

        backgroundStyle.setFillBackgroundColor(IndexedColors.GREY_50_PERCENT.getIndex());
        backgroundStyle.setFillPattern(CellStyle.soLID_FOREGROUND);

        CellStyle borderStyle = workbook.createCellStyle();

        borderStyle.setBorderBottom(CellStyle.BORDER_THIN);
        borderStyle.setBottomBorderColor(IndexedColors.BLACK.getIndex());
        borderStyle.setBorderLeft(CellStyle.BORDER_THIN);
        borderStyle.setLeftBorderColor(IndexedColors.BLACK.getIndex());
        borderStyle.setBorderRight(CellStyle.BORDER_THIN);
        borderStyle.setRightBorderColor(IndexedColors.BLACK.getIndex());
        borderStyle.setBorderTop(CellStyle.BORDER_THIN);
        borderStyle.setTopBorderColor(IndexedColors.BLACK.getIndex());

        for (int i = 1; i <= x; i++) {
            Row row = sheet.createRow(i - 1);

            for (int j = 1; j <= y; j++) {
                Cell cell = row.createCell(j - 1);
                cell.setCellValue(i * j);
                cell.setCellStyle(borderStyle);

                if (cell.getRowIndex() == 0 || cell.getColumnIndex() == 0) {
                    cell.setCellStyle(backgroundStyle);
                }
            }
        }

        FileOutputStream out = new FileOutputStream(fileName);
        workbook.write(out);
        out.close();
    }
}