NSString *urlStr = @"https://";
   // NSURL *Url = [NSURL URLWithString:@"https://"];

 NSArray *cookiesArray = [[NSHTTPCookieStorage sharedHTTPCookieStorage] cookiesForURL:[NSURL URLWithString:urlStr]];
    NSString *jsession ;

    for (NSHTTPCookie *cookie in cookiesArray) {
        if ([cookie.name isEqualToString:@"JSESSIONID"]) {
            jsession = nil;
            jsession = cookie.value;
            break;
        }
    }

循环后得到的便是JSESSIONID