FileMD5Util.java

package com.app.mvc.util;

import lombok.extern.slf4j.Slf4j;

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

/**
 * Created by jimin on 15/11/29.
 */
@Slf4j
public class FileMD5Util {

    protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

    protected static MessageDigest messageDigest = null;

    static {
        try {
            messageDigest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            log.error("{} 初始化失败，MessageDigest不支持MD5!", FileMD5Util.class.getName(), e);
        }
    }

    public static String getFileMD5WithoutException(File file) {
        try {
            return getFileMD5String(file);
        } catch (Throwable e) {
            log.error("计算文件md5失败, {}", file.getName(), e);
            return "";
        }
    }

    public static String getFileMD5String(File file) throws IOException {
        FileInputStream in = new FileInputStream(file);
        FileChannel ch = in.getChannel();

        //700000000 bytes are about 670M
        int maxSize = 700000000;

        long startPosition = 0L;
        long step = file.length() / maxSize;

        if (step == 0) {
            MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0, file.length());
            messageDigest.update(byteBuffer);
            return bufferToHex(messageDigest.digest());
        }

        for (int i = 0; i < step; i++) {
            MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, startPosition, maxSize);
            messageDigest.update(byteBuffer);
            startPosition += maxSize;
        }

        if (startPosition == file.length()) {
            return bufferToHex(messageDigest.digest());
        }

        MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, startPosition, file.length() - startPosition);
        messageDigest.update(byteBuffer);

        return bufferToHex(messageDigest.digest());
    }

    public static String getMD5String(String s) {
        return getMD5String(s.getBytes());
    }

    public static String getMD5String(byte[] bytes) {
        messageDigest.update(bytes);
        return bufferToHex(messageDigest.digest());
    }

    private static String bufferToHex(byte bytes[]) {
        return bufferToHex(bytes, 0, bytes.length);
    }

    private static String bufferToHex(byte bytes[], int m, int n) {
        StringBuffer stringbuffer = new StringBuffer(2 * n);
        int k = m + n;
        for (int l = m; l < k; l++) {
            appendHexPair(bytes[l], stringbuffer);
        }
        return stringbuffer.toString();
    }

    private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
        char c0 = hexDigits[(bt & 0xf0) >> 4];
        char c1 = hexDigits[bt & 0xf];
        stringbuffer.append(c0);
        stringbuffer.append(c1);
    }

    public static boolean checkPassword(String password, String md5PwdStr) {
        String s = getMD5String(password);
        return s.equals(md5PwdStr);
    }

}