做加密时，传到后台出现%20 %3D等，导致解密错误，原因是特殊字符被转义编码，解决方案：
try {
ciphertext = URLDecoder.decode(ciphertext,"UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
来源：这位大佬写的。https://blog.csdn.net/zhizhengguan/article/details/89066930