java怎么读取很大的excel(20w条数据)，怎么通过字节流获取到单元格的内容

使用java poi
package webservice;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;

public class ExcelController {

@SuppressWarnings("deprecation")
public void excel() throws FileNotFoundException, IOException{

String filename = "d:\\excel.xls";
HSSFWorkbook workbook = new HSSFWorkbook(new FileInputStream(filename));
//按名引用excel工作表
// HSSFSheet sheet = workbook.getSheet("JSP");
//也可以用以下方式来获取excel的工作表，采用工作表的索引值
HSSFSheet sheet = workbook.getSheetAt(0);
HSSFRow row ;
HSSFCell cell1;
int rows=sheet.getLastRowNum();
for(int icount=0;icount row = sheet.getRow(icount);
int line=row.getPhysicalNumberOfCells();
for(int j=0;j cell1= row.getCell(j);
System.out.println(cell1+"--"+icount+"---"+j);
}
}
//打印读取值
// System.out.println(cell.getStringCellValue());

//新建一输出流
FileOutputStream fout = new FileOutputStream(filename); //PS：filename 是你另存为的路径，不处理直接写入模版文件
//存盘
workbook.write(fout);
fout.flush();
//结束关闭
fout.close();

}

public HSSFCell getCell(HSSFRow row, int index) {

// 取得分发日期单元格
HSSFCell cell = row.getCell(index);

// 如果单元格不存在
if (cell == null) {

// 创建单元格
cell = row.createCell(index);
}

// 返回单元格
return cell;
}

public static void main(String[] args) {
ExcelController ec = new ExcelController();
try {
ec.excel();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}