用JXL包操作Excel文件

import java.io.File;
import java.util.Date;
import jxl.Sheet;
import jxl.Workbook;
import jxl.format.UnderlineStyle;
import jxl.write.DateFormat;
import jxl.write.DateTime;
import jxl.write.Label;
import jxl.write.NumberFormat;
import jxl.write.WritableCellFormat;
import jxl.write.WritableFont;
import jxl.write.WritableImage;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;
import jxl.write.WriteException;
import jxl.write.Number;
import jxl.write.Boolean;

public class ExcelParse ...{
    WritableWorkbook wwk;

    public WritableWorkbook getWritableWorkbook() ...{
        return wwk;
    }

    public void setWritableWorkbook(WritableWorkbook wwk) ...{
        this.wwk = wwk;
    }

    public WritableWorkbook newWritableWorkbook(String fileName)
            throws Exception ...{
        WritableWorkbook wwk = Workbook.createWorkbook(new File(fileName));
        return wwk;
    }

    public void addSheet(String sheetName, int index) throws Exception ...{
        wwk.createSheet(sheetName, index);
        // wwk.write();//若增加此一行,则只能创建第一个sheet
    }

    public void removeSheet(int index) throws Exception ...{
        wwk.removeSheet(index);
    }

    public void setLabel(WritableSheet sheet, int column, int row, String value)
            throws WriteException ...{
        Label labelCell = new Label(column, row, value);
        sheet.addCell(labelCell);
    }

    // 格式化输入字符串
    public void setFormatLabel(WritableSheet sheet, int column, int row,
            String value, WritableFont writableFont) throws WriteException ...{
        // WritableFont writableFont=new
        // writableFont(WritableFont.ARIAL,10,WritableFont.NO_BOLD,false,
        // UnderlineStyle.NO_UNDERLINE,jxl.format.Colour.RED);
        WritableCellFormat writableCellFormat = new WritableCellFormat(
                writableFont);
        Label labelCell = new Label(column, row, value, writableCellFormat);
        sheet.addCell(labelCell);
    }

    public void setNumber(WritableSheet sheet, int column, int row, double value)
            throws WriteException ...{
        Number numCell = new Number(column, row, value);
        sheet.addCell(numCell);
        // this.setFormatNumber(sheet, column, row, value, null);//行不通,报空指针异常
    }

    // 格式化输入数字
    public void setFormatNumber(WritableSheet sheet, int column, int row,
            double value, String format) throws WriteException ...{
        NumberFormat numberFormat = new NumberFormat(format);
        WritableCellFormat cellFormat = new WritableCellFormat(numberFormat);
        Number numCell = new Number(column, row, value, cellFormat);
        sheet.addCell(numCell);
    }

    public void setBoolean(WritableSheet sheet, int column, int row,
            boolean value) throws WriteException ...{
        Boolean boolCell = new Boolean(column, row, value);
        sheet.addCell(boolCell);
    }

    public void setDateTime(WritableSheet sheet, int column, int row, Date value)
            throws WriteException ...{
        DateTime dateCell = new DateTime(column, row, value);
        sheet.addCell(dateCell);
    }

    // 格式化输入日期
    public void setFormatDateTime(WritableSheet sheet, int column, int row,
            Date value, String format) throws WriteException ...{
        DateFormat dateFormat = new DateFormat(format);
        WritableCellFormat cellFormat = new WritableCellFormat(dateFormat);
        DateTime dateCell = new DateTime(column, row, value, cellFormat);
        sheet.addCell(dateCell);

    }

    public void setImage(WritableSheet sheet, int fromColumn, int fromRow,
            int toColumn, int toRow, String imageUri) throws WriteException ...{
        File f = new File(imageUri);
        WritableImage imageCell = new WritableImage(fromColumn, fromRow,toColumn,toRow, f);
        sheet.addImage(imageCell);
    }

    public Workbook getWorkbook(String fileName) throws Exception ...{
        Workbook wkb = Workbook.getWorkbook(new File(fileName));
        return wkb;
    }

    public Sheet[] getSheets() ...{
        return wwk.getSheets();
    }

    public void close() throws Exception ...{
        wwk.write();
        this.wwk.close();
    }

    public static void main(String[] args) throws Exception ...{
        ExcelParse ep = new ExcelParse();
        ep.setWritableWorkbook(ep.newWritableWorkbook("create.xls"));
        ep.addSheet("firstSheet", 0);
        ep.addSheet("thirdSheet", 1);// index不一定是一系列连接数
        ep.addSheet("secondSheet", 1);// 位置第二位,后面的后移一位
        ep.removeSheet(0);
        WritableSheet sheet = (WritableSheet) ep.getSheets()[0];
        int column = 2, row = 2;
        ep.setBoolean(sheet, column++, row++, false);
        ep.setDateTime(sheet, column++, row++, new Date());
        ep.setLabel(sheet, column++, row++, "String label");
        ep.setNumber(sheet, column++, row++, 3.1415926);
        ep.setImage(sheet, 5, 10, 10, 20, "sunset.png");
        ep.close();
        // Workbook workbook=ep.getWorkbook("create.xls");
    }
}

疑问:如果只修改Excel中的一小部分该如何?

import java.io.File;

import jxl.CellType;
import jxl.Workbook;
import jxl.write.Label;
import jxl.write.WritableCell;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;
public class ExcelUpdate ...{
    public static void main(String[] args)throws Exception...{
        Workbook rwb=Workbook.getWorkbook(new File("create.xls"));
        WritableWorkbook wwb=Workbook.createWorkbook(new File("b.xls"),rwb);//把create.xls复制到b.xls
        WritableSheet ws=wwb.getSheet(0);
        WritableCell wc=ws.getWritableCell(2,2);
        if(wc.getType()==CellType.LABEL)...{
            Label label=(Label)wc;
            label.setString("The value has been modified");
            //不需要这行,不然异常:Cell has already been added to a worksheet
            //ws.addCell(label);
        }
        wwb.write();
        wwb.close();
        rwb.close();
        
    }
}