java - What characters will never be in a tomcat/spring boot session id? -

in spring boot app, want pass combined variable 1 rest service, out through user interface, , through second rest service. accomplish this, want first rest service create 1 single string concatenating session id different string representing else, , separator value marking break between 2 strings, string combined = sessionid+separatorcharacter+someotherstring. this, second rest service accept combined string @requestparam, , decompose string session id , other value.

i use string.split() split 2 parts of combined string using separator value, like:

string[] parts = string.split("separatorcharacter"); string sessionid = parts[0]; string someotherstring = parts[1]; 

but what characters can choose when creating marker separating 2 parts of string? combined string used url parameter, has able cross internet in http requests , never present in session id produced spring or tomcat. also, 1 of strings going base64 encoded, separator character needs survive encode/decode process. i decode before splitting, don't need worry characters used while encoded.

but, in case matters, encode/decode is:

import java.io.ioexception; import java.security.messagedigest; import java.security.nosuchalgorithmexception; import java.text.parseexception; import java.text.simpledateformat; import java.util.arraylist; import java.util.date; import java.util.list; import java.util.random;  import sun.misc.base64decoder; import sun.misc.base64encoder;  public class stringutil {      private static random random = new random((new date()).gettime());      public static string encrypt(string userid) {           base64encoder encoder = new base64encoder();         byte[] salt = new byte[8];         random.nextbytes(salt);         return encoder.encode(salt)+encoder.encode(userid.getbytes());     }      public static string decrypt(string encryptkey) {         if (encryptkey.length() > 12) {             string cipher = encryptkey.substring(12);             base64decoder decoder = new base64decoder();             try {                 return new string(decoder.decodebuffer(cipher));             } catch (ioexception e) {}         }              return null;     } }