根据UUID和MD5， 生成可以用作Token的字符串

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;

public class MD5Generator
{
    private static final char[] hexCode = "0123456789abcdef".toCharArray();

    public String generateValue(){
        return generateValue(UUID.randomUUID().toString());
    }

    public static String toHexString(byte[] data)
    {
      if (data == null) {
        return null;
      }
      StringBuilder r = new StringBuilder(data.length * 2);
      byte[] arrayOfByte = data; int j = data.length; for (int i = 0; i < j; i++) { byte b = arrayOfByte[i];
        r.append(hexCode[(b >> 4 & 0xF)]);
        r.append(hexCode[(b & 0xF)]);
      }
      return r.toString();
    }

    public String generateValue(String param) {
        try {
            MessageDigest algorithm;
            algorithm = MessageDigest.getInstance("MD5");
            algorithm.reset();
            algorithm.update(param.getBytes());
            byte[] messageDigest = algorithm.digest();
            return toHexString(messageDigest);
        } catch (NoSuchAlgorithmException e) {
            LOG.error(e.getMessage());
            throw new WebApplicationException(Response.Status.INTERNAL_SERVER_ERROR);
        }

    }
}