【IO面试题】打印目录树形结构，并输出到file.txt中

package com.peter.solution;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;

/**
 * 打印目录树形结构，并输出到file.txt中
 * @author Peter
 *
 */

public class IOSolution {
    
    public static Writer out=null;
    
    public static void solution(String path,int level) throws IOException{
        if(out==null){
            out=new FileWriter("file.txt");
        }
        File file=new File(path);
        if(file.exists()){
            if (file.isFile()) {
                for(int i=0;i<level;i++){
                    out.write("\t");
                }
                out.write("|-->"+file.getName()+"\n");
            }else{
                for(int i=0;i<level;i++){
                    out.write("\t");
                }
                out.write(file.getName()+"\n");
                File[] files=file.listFiles();
                if(files!=null){
                    for(File f:files){
                        solution(f.getPath(),level+1);
                    }
                }
            }
        }
        out.flush();
        if(level==0){
            out.close();
        }
    }
    
    public static void main(String[] args) {
        try {
            solution("C:\\Users\\lenovo\\Downloads\\5",0);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}