public static String replaceSpace(StringBuffer str) {
int oldLength = str.length();
for (int i = 0; i < oldLength; i++) {
if (str.charAt(i)==' '){
str.append(" ");
}
}
int newLength = str.length();
for (int i = oldLength-1; i >=0 ; i--) {
if (str.charAt(i)==' '){
str.setCharAt(--newLength,'0');
str.setCharAt(--newLength,'2');
str.setCharAt(--newLength,'%');
}else {
str.setCharAt(--newLength,str.charAt(i));

}
}
return str.toString();
}