Finding Session id for User in Future Method or Batch Class

APICallUtilityVF.page

<apex:page showHeader="true" sidebar="true">
	SessionIDStart{!$Api.Session_ID}SessionIDEnd
	StartVFPageBaseURL{!LEFT($CurrentPage.URL,FIND('/',$CurrentPage.URL,9))}EndVFPageBaseURL
</apex:page>

SessionIdUtility.cls

//Author- sunil Kumar
//Twitter handle-@sunil02kumar
//purpose- finding user sessionid in asynchrounous apex call
public class SessionIdUtility{
    @future(callout=true)
    public static void checkIfUserSessionIdExistInFutureCall(){
        HttpRequest req = new HttpRequest();
        system.debug('********session Id using UserInfo.getSessionID():'+UserInfo.getSessionID());
        string sessionId=findSessionIdUsingVFPage(Page.APICallUtilityVF);
        system.debug('********session Id by generating from VF:'+sessionId); 
       
    }

    public  static String findSessionIdUsingVFPage(PageReference visualforcePage){
        String content = visualforcePage.getContent().toString();
        Integer startIndex = content.indexOf('SessionIDStart') + 'SessionIDStart'.length(),
                endIndex = content.indexOf('SessionIDEnd');
        return content.substring(startIndex, endIndex);
    }  
}