public String replaceSpace(StringBuffer str) { char[] chara = str.toString().toCharArray();
    String result =""; for (int i=0 ;i<str.length();i++) {
        String tmp = String.valueOf(chara[i]); if(tmp.equals(" ")){
            result+="%20";
        }else {
            result +=tmp;
        }
    } return result;
}