生成字符串和文件的MD5

本文介绍如果根据字符串和文件内容生成MD5值：

根据字符串生成MD5 根据文件内容生成MD5

根据字符串生成MD5

根据输入的字符串生成与改字符串对应的MD5值。

实现

主程序strMD5，这里调用了bufferToHex将byte转为字符串

public static String strMD5(String strSrc) {
        String md5Str = "";
        try {
            MessageDigest messageDigest = MessageDigest.getInstance("MD5");
            messageDigest.reset();
            byte[] bt = strSrc.getBytes();
            messageDigest.update(bt);
            md5Str = bufferToHex(messageDigest.digest());
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return md5Str;
    }

bufferToHex，将byte转为字符串

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

    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);
    }

根据文件内容生成MD5

根据文件的内容生成对应的MD5值。即便文件名称一致但是内容不同MD5值不同。

实现

主程序getFileMD5，利用BigInteger生成32位16进制数

private static int bufferSize = 256 * 1024;
    private static FileInputStream fileInputStream = null;
    private static DigestInputStream digestInputStream = null;

    public static String getFileMD5String(File file) throws IOException {
        if (!file.isFile()) {
            return null;
        }
        try {
            MessageDigest messageDigest =MessageDigest.getInstance("MD5"); 
            fileInputStream = new FileInputStream(file);
            digestInputStream = new DigestInputStream(fileInputStream,messageDigest);
            byte[] buffer =new byte[bufferSize];
            while (digestInputStream.read(buffer) > 0);
            messageDigest= digestInputStream.getMessageDigest(); 
            byte[] resultByteArray = messageDigest.digest(); 
            BigInteger bigInt = new BigInteger(1, resultByteArray);
            String md5 = bigInt.toString(16);
            int length = md5.length();
            for (int i = 0; i < (32 - length); i++) {
                md5 = 0 + md5;
            }
            return md5.toUpperCase();
//          return bufferToHex(resultByteArray).toUpperCase();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        } finally {
            if (fileInputStream != null) {
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(digestInputStream!=null){
                digestInputStream.close();
            }
        }
    }