java string output in reverse order of words

String str = "hi,hello world !";
 
// separator
char[] splits = ", ".toCharArray();
Set<Character> splitCharSet = new HashSet<Character>();
for(char split:splits){
    splitCharSet.add(split);
}

StringBuilder reverseStr = new StringBuilder();

StringBuilder rsIndex = new StringBuilder();

Character indexChar;

for(int i=str.length()-1;i>-1;i--){

    indexChar = Character.valueOf(str.charAt(i));

    if(!splitCharSet.contains(indexChar)){

        rsIndex.append(indexChar);

    }else{

        reverseStr.append(rsIndex.reverse()).append(indexChar);

        rsIndex.delete(0, rsIndex.length());

    }

}

reverseStr.append(rsIndex.reverse());

System.out.println(reverseStr);