把输入的句子的每一个单词的拼写反转显示，但是单词的位置不变

import java.util.Stack;

public class WordsReverse2 {

??? public static void main(String[] args) {
??????? System.out.println(reverse("Hello World!"));
??? }

??? /**
???? * 实现一个函数，把输入的句子的每一个单词的拼写反转显示，但是单词的位置不变。 <br>
???? * 例如 输入：Hello World! 输出：olleH !dlroW
???? *
???? */
??? public static String reverse(String str) {
??????? if (str == null || str.trim().equals("")) {
??????????? return str;
??????? }
??????? StringBuilder re = new StringBuilder();
??????? Stack<Character> stack = new Stack<Character>();
??????? for (int length = str.length(), i = 0; i < length; i++) {
??????????? char ch = str.charAt(i);
??????????? if (ch == ' ' || i == length - 1) {
??????????????? while (!stack.isEmpty()) {
??????????????????? re.append(stack.pop());
??????????????? }
??????????????? re.append(ch);
??????????? } else {
??????????????? stack.push(ch);
??????????? }
??????? }
??????? return re.toString();
??? }

}