java 获取文件MD5值

    private final char[] hexCode = "0123456789ABCDEF".toCharArray();

    public String toHexString(byte[] data) {
        StringBuilder r = new StringBuilder(data.length * 2);
        for (byte b : data) {
            r.append(hexCode[(b >> 4) & 0xF]);
            r.append(hexCode[(b & 0xF)]);
        }
        return r.toString();
    }

    public String getFileMD5(File file) {
        if (!file.exists() || !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)) > 0) {
                digest.update(buffer, 0, len);
            }
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return toHexString(digest.digest());
    }

    public String getFileMD5(String filepath) {
        File file = new File(filepath);
        return getFileMD5(file);
    }