import org.apache.commons.codec.digest.DigestUtils;

String sign = DigestUtils.md5Hex(string);

方法片段：

import java.security.MessageDigest;

try {

            byte[] array = computeHash(params);

            StringBuilder stringBuilder = new StringBuilder();

            for (int i = 0; i < array.length; i++) {

                byte b = array[i];

                String text = Integer.toHexString(b & 0xFF);

                if (text.length() == 1) {

                    stringBuilder.append("0");

                }

                stringBuilder.append(text);

            }

            return stringBuilder.toString();

        } catch (NoSuchAlgorithmException e) {

            e.printStackTrace();

        }

============================

public static byte[] computeHash(String input) throws NoSuchAlgorithmException {

        MessageDigest digest = MessageDigest.getInstance("MD5");

        digest.reset();

        byte[] utf8bytes = null;

        try {

            utf8bytes = input.getBytes("UTF-8");

            // digest.update(utf8bytes);

        } catch (UnsupportedEncodingException e) {

            e.printStackTrace();

        }

        return digest.digest(utf8bytes);

    }