请老师看一下到底哪里有问题,没有输出结果,也没下载

package com.imooc.downloader;

import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Downloader {

    private Integer threadNum=10;
    /**
     *下载单个文件保存到本地
     * @param source 原图片地址
     * @param targetDir 目标目录,下载后的图片保存位置
     */
    public void download(String source,String targetDir){
        InputStream is = null;
        OutputStream os=null;
        try{
            //https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-11572548.jpeg
            //substring字符串截取            截取最后一个斜杠字符出现开始之后的字符
            String fileName=source.substring(source.lastIndexOf("/")+1);
            File targetFile=new File(targetDir+"/"+fileName);
            //确保文档创建成功
            if(!targetFile.exists()){
                targetFile.createNewFile();
            }

            URL url = new URL(source);
            URLConnection connection=url.openConnection();
            is=connection.getInputStream();
            os=new FileOutputStream(targetFile);

            byte[] bs = new byte[1024];
            int len=0;
            while((len=is.read(bs))!=-1){
                os.write(bs,0,len);
            }
            //                                 来源网址   换行,缩进   目标保存路径              向下取整       文件长度除以1024
            System.out.println("[INFO]图片下载完成"+source+"\n\t ->"+targetFile.getPath()+"("+Math.floor(targetFile.length()/1024)+"kb)");

        }catch(IOException e){
            e.printStackTrace();
        }finally{
            try {
                if (os != null) {
                    os.close();
                }
                if (is != null) {
                    is.close();
                }
            }catch(IOException e){
                e.printStackTrace();
            }
        }
    }



    /**
     *从指定文件读取下载地址,批量下载网络资源
     * @param targetDir 下载文件的储存目录
     * @param downloadTxt downloade.txt完整路径
     */
    public void multiDownloadFromFile(String targetDir,String downloadTxt){
        //目录实例
        File dir = new File(targetDir);
        if(!dir.exists()){
            dir.mkdirs();//目录创建方法,有s的是多级目录
            System.out.println("[INFO]发现下载目录["+dir.getPath()+"]不存在,已自动创建");
            //读取download.txt存入resoures集合
            List<String> resources = new ArrayList<>();
            BufferedReader reader=null;
            ExecutorService threadPool=null;
            try{
                reader = new BufferedReader(new FileReader(downloadTxt));
                String line=null;
                while((line=reader.readLine())!=null){
                    resources.add(line);
                    //System.out.println(line);
                }
                threadPool= Executors.newFixedThreadPool(this.threadNum);
                //直接在for循环中使用this.实现类调用的是匿名实现类runnable,因此需要用that转换
                Downloader that=this;
                for(String res:resources){
                    threadPool.execute(new Runnable() {
                        @Override
                        public void run() {
                            that.download(res,targetDir);
                        }
                    });
                }
            }catch(IOException e){
                e.printStackTrace();
            }finally {
                if(threadPool!=null){
                    threadPool.shutdown();
                }
                if(reader!=null){
                    try {
                        reader.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }



    //开始多线程下载的方法
    public void start(String propDir){
        //实例文件指定路径
        File propFile=new File(propDir+"\\config.properties");
        //实例properties类
        Properties properties = new Properties();
        //加载配置文件
        Reader reader=null;
        try {
            reader=new FileReader(propFile);
            //加载文件里的数据
            properties.load(reader);
            //读取数据,getproperty根据属性名获取对应的值
            String threadNum=properties.getProperty("thread-num");
            this.threadNum = Integer.parseInt(threadNum);
            String targetDir = properties.getProperty("target-dir");
//          System.out.println(threadNum);
//          System.out.println(targetDir);
            this.multiDownloadFromFile(targetDir,propDir+"\\download.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(reader!=null){
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public static void main(String[] args) {
        Downloader downloader=new Downloader();
        downloader.start("D:\\JAVA\\imooc\\慕课Java练习\\downloader\\src");
        //downloader.download("https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-11572548.jpeg","d:/JavaIO");
    }
}

config-properties:

==

download.txt:

https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-11572548.jpeg
https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-11593467.jpeg
https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-11631922.jpeg
https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-12203460.jpeg
https://manongbiji.oss-cn-beijing.aliyuncs.com/imooc/pexels/pexels-photo-12240136.jpeg