Java 计算文件的MD5值（代码）

import com.alibaba.fastjson.JSON;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.HashMap;
import java.util.Map;

/**
 * @author jasonLu
 * @date 2017/6/1 11:33
 * @Description:
 */
public class CalacFileMd5
{
    /**
     * 获取单个文件的MD5值！
     *
     * @param file
     * @return
     */
    public static String getFileMD5(File file)
    {
        if (!file.isFile())
        {
            return null;
        }
        MessageDigest digest = null;
        FileInputStream in = null;
        byte buffer[] = new byte[1024];
        int len;
        try
        {
            digest = MessageDigest.getInstance("MD5");
            in = new FileInputStream(file);
            while ((len = in.read(buffer, 0, 1024)) != -1)
            {
                digest.update(buffer, 0, len);
            }
            in.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return null;
        }
        BigInteger bigInt = new BigInteger(1, digest.digest());
        return bigInt.toString(16);
    }

    /**
     * 获取文件夹中文件的MD5值
     *
     * @param file
     * @param listChild
     *         ;true递归子目录中的文件
     * @return
     */
    public static Map<String, String> getDirMD5(File file, boolean listChild)
    {
        if (!file.isDirectory())
        {
            return null;
        }
        //<filepath,md5>
        Map<String, String> map = new HashMap<>();
        String md5;
        File files[] = file.listFiles();
        for (File f : files)
        {
            if (f.isDirectory() && listChild)
            {
                map.putAll(getDirMD5(f, listChild));
            }
            else
            {
                md5 = getFileMD5(f);
                if (md5 != null)
                {
                    map.put(f.getPath(), md5);
                }
            }
        }
        return map;
    }

    public static void main(String[] args)
    {
        String filePath = "E:/testQs";
        File file = new File(filePath);
        Map<String, String> map = getDirMD5(file, true);

        String json = JSON.toJSONString(map);

        writeToFile(json);

    }

    private static void writeToFile(String str)

    {
        OutputStreamWriter out = null;
        try
        {
            out = new OutputStreamWriter(new FileOutputStream("E:/FileMD5.json"), "UTF-8");
            out.write(str);
            out.flush();
            out.close();

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