開發中遇到對視頻文件的md5的檢測判斷，經常會發生OOM。
解決辦法如下：

public class MD5Util {
 
    public static String getMd5ByFile(File file) {
        InputStream fis;
        byte[] buffer = new byte[2048];
        int numRead = 0;
        MessageDigest md5;

        try {
            fis = new FileInputStream(file);
            md5 = MessageDigest.getInstance("MD5");
            while ((numRead = fis.read(buffer)) > 0) {
                md5.update(buffer, 0, numRead);
            }
            fis.close();
            return md5ToString(md5.digest());
        } catch (Exception e) {
            System.out.println("error");
            return null;
        }
    }

    public static String md5ToString(byte[] md5Bytes) {
        StringBuffer hexValue = new StringBuffer();
        for (int i = 0; i < md5Bytes.length; i++) {
            int val = ((int) md5Bytes[i]) & 0xff;
            if (val < 16) {
                hexValue.append("0");
            }
            hexValue.append(Integer.toHexString(val));
        }
        return hexValue.toString();
    }

}