StringTokenizer

String arr = "a,b,c";

String str = "b";

StringTokenizer st = new StringToKenizer(arr, ",");

if(null != st && st.countTokens() != 0){

  String tmp = "";

  while(str.hasMoreTokens()){

    tmp = (String)st.nextToken();

    if(tmp.equals(str)){

      OK

      break;

    }

  }

}