java 批量计算某个文件夹下所有文件的md5

1.需要的jar包
poi-3.14-20160307.jar
poi-ooxml-3.14-20160307.jar
poi-ooxml-schemas-3.14-20160307.jar
xmlbeans-2.6.0.jar
2. 完整代码如下：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.security.MessageDigest;

import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

//批量计算文件夹下的md5
public class calc_md5 {
	static XSSFWorkbook workbook = new XSSFWorkbook();
	static XSSFSheet sheet = workbook.createSheet("测试");
	static XSSFRow row = sheet.createRow(0); //表头
	static int i = 1;
	
	public static void main(String[] args) throws IOException {
		File f = new File("xxx");//要计算md5的文件夹路径	
		String filename = f.getName();
		//设置表头名称
		row.createCell(0).setCellValue("文件名");
		row.createCell(1).setCellValue("md5");
		findFile(f);		
		FileOutputStream fileOut = new FileOutputStream("xxx.xlsx");
		workbook.write(fileOut);//将计算结果保存到xxx.xlsx
		fileOut.flush();
		fileOut.close();
		workbook.close();
	}
	
	//遍历文件夹，写入excel
	public static void findFile(File f) throws IOException {//计算md5并写入excel
				
		File[] flist = f.listFiles();
		for (File file : flist) { 
			if(file.isDirectory()) {
				findFile(file); //递归遍历文件夹下的所有文件
			}else {
				String md5 = getMd5(file.getAbsolutePath());
				XSSFRow newrow = sheet.createRow(i);
				newrow.createCell(0).setCellValue(file.getName());
				newrow.createCell(1).setCellValue(md5);
				i++;
			}			
		}		
	}
	//计算单个文件的md5
	public  static String getMd5(String path) {
		BigInteger bi = null;
		try {
			byte[] buffer = new byte[8192];
			int len = 0;
			MessageDigest md = MessageDigest.getInstance("MD5");
			File f = new File(path);
			FileInputStream fis = new FileInputStream(f);
			while((len=fis.read(buffer))!=-1) {
				md.update(buffer, 0, len);
			}
			fis.close();
			byte[] b = md.digest();
			bi = new BigInteger(1,b);		
		}catch(Exception e) {
			e.printStackTrace();
		}
		
		return bi.toString(16).length()==32?bi.toString(16):"0"+bi.toString(16);
		//BigInteger会排除第一个0，所以如果不等于32就是第一个0被抹掉了，这里给它加上
	}

}