请用递归和迭代两种方式输出文件目录结构

示例：输出一个目录的文件结构如下图所示：

控制台输出如下：

递归

新建文件夹

   a.txt

   新建文件夹

      b.txt

迭代

新建文件夹

   a.txt

   新建文件夹

      b.txt

代码如下：

import java.io.File;
import java.util.Stack;

/**
* Created by liyiwen1 on 2016/11/17.
*/
public class a {
public static void main(String[] args) {
System.out.println("递归");
printDir(new File("C:\\Users\\liyiwen1\\Desktop\\新建文件夹"),"");
System.out.println("迭代");
iterationPrintDir(new File("C:\\Users\\liyiwen1\\Desktop\\新建文件夹"),"");
}

//递归实现
public static void printDir(File file){
printDir(file, "");
}

//迭代实现
public static void iterationPrintDir(File file){
iterationPrintDir(file, "");
}

static class DataUnit{
private File file;
private String soujin;

public DataUnit(File file, String soujin) {
this.file = file;
this.soujin = soujin;
}

public File getFile() {
return file;
}

public void setFile(File file) {
this.file = file;
}

public String getSoujin() {
return soujin;
}

public void setSoujin(String soujin) {
this.soujin = soujin;
}
}

public static void iterationPrintDir(File file, String soujin){//soujin表示缩进
Stack<DataUnit> stack = new Stack();
stack.push(new DataUnit(file, soujin));
while (!stack.isEmpty()){
file = stack.peek().getFile();
soujin = stack.peek().getSoujin();
stack.pop();

if (!file.exists()){
return;
}

if (file.isFile()){
System.out.println(soujin + file.getName());
}else if (file.isDirectory()){
System.out.println(soujin + file.getName());
String[] files = file.list();
if (files != null && files.length !=0){
for (String fileName : files){
File ziFile = new File(file, fileName);
if (ziFile.exists() && ziFile.isFile()){
System.out.println(soujin +" " + fileName);
}else if (ziFile.exists() && ziFile.isDirectory()){
stack.push(new DataUnit(ziFile," " + soujin));
}
}
}
}

}

}

public static void printDir(File file, String soujin){//soujin表示缩进
if (!file.exists()){
return;
}

if (file.isFile()){
System.out.println(soujin + file.getName());
}else if (file.isDirectory()){
System.out.println(soujin + file.getName());
String[] files = file.list();
if (files != null && files.length !=0){
for (String fileName : files){
File ziFile = new File(file, fileName);
if (ziFile.exists() && ziFile.isFile()){
System.out.println(soujin +" " + fileName);
}else if (ziFile.exists() && ziFile.isDirectory()){
printDir(ziFile, " " + soujin);
}
}
}
}
}

}