有会 C# 转 Java 代码么，求教如下代码。谢谢

public static string Sign(string prestr, string key, string _input_charset)
{
StringBuilder sb = new StringBuilder(32);

        prestr = prestr + key;

        MD5 md5 = new MD5CryptoServiceProvider();
        byte[] t = md5.ComputeHash(Encoding.GetEncoding(_input_charset).GetBytes(prestr));
        for (int i = 0; i < t.Length; i++)
        {
            sb.Append(t[i].ToString("x").PadLeft(2, '0'));
        }

        return sb.ToString();
    }