java面试题 字符串安顺序写入文件

有一个字符串accceeeesd要按一定的顺序写入文件（保存到d盘的test.txt文件中）

得到的结果是：

a

ccc

d

eeee

s

package demo;

import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class Test {

public static void main(String[] args) {
String str = "accceeeesd";
sortString(str,"D:/test.txt");

}

public static void sortString(String str,String path){
char[] ch = str.toCharArray();
Set<Character> chs = new TreeSet<Character>();

for (int i = 0; i < ch.length; i++) {
chs.add(ch[i]);
}

Iterator<Character> ia = chs.iterator();
FileWriter w = null;
try {
w = new FileWriter(path);
while(ia.hasNext()){
char c = ia.next();
for (int i = 0; i < ch.length; i++) {
if(c==ch[i]){
System.out.print(c);
w.write(c);
}
}
System.out.println();
w.write("\r\n");
}
} catch (IOException e) {
e.printStackTrace();
}
}
}