万事开头难--获取文件MD5

话不多说直接上码，菜鸟一枚，大家希望多多指点

package com.learn.java.file;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;

/**
 * Created by 尚晓琼 on 2017/9/28.
 */
public class FileMD5 {

    public String getMd5ByFile(File file) throws FileNotFoundException {
        FileInputStream in = new FileInputStream(file);
        StringBuffer sb = new StringBuffer();
        try {
            FileChannel channel = in.getChannel();
            long position = 0;
            long total = file.length();
            long page = 1024 * 1024 * 500;
            MessageDigest md5 = MessageDigest.getInstance("MD5");
            while (position < total) {
                long size = page <= total - position ? page : total - position;
                MappedByteBuffer byteBuffer = channel.map(FileChannel.MapMode.READ_ONLY, position, size);
                position += size;
                md5.update(byteBuffer);
            }
            byte[] b = md5.digest();

            for (int i = 0; i < b.length; i++) {
                sb.append(byteToChars(b[i]));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {

            try {
                in.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return sb.toString();
    }

    private char[] byteToChars(byte b) {
        int h = ((b & 0xf0) >> 4);
        int l = (b & 0x0f);
        char[] r = new char[2];
        r[0] = intToChart(h);
        r[1] = intToChart(l);

        return r;
    }

    private char intToChart(int i) {
        if (i < 0 || i > 15) {
            return ' ';
        }
        if (i < 10) {
            return (char) (i + 48);
        } else {
            return (char) (i + 55);
        }
    }
}

期望

• 实现md5秒传。。。只是最近好像没什么时间···