多线程项目实战——多线程下载器

多线程项目实战——多线程下载器 多线程下载器

最近学习了多线程相关知识，通过一个小项目对所学知识梳理，做一个综合的运用。

项目介绍

该项目主要是使用HttpURLConection发起HTTP请求，再结合IO流和多线程对文件进行一个切分下载，最后合并。

项目演示

项目目录结构

代码

项目入口类，需要传入下载地址，或者在控制台输入

public class Main {

    public static void main(String[] args) {
        //下载地址
        String url = null;
        if (args == null || args.length == 0) {
            while (url == null) {
                LogUtils.info("请输入下载地址");
                Scanner scanner = new Scanner(System.in);
                url = scanner.next();
            }
        }else {
            url = args[0];
        }

        Downloader downloader = new Downloader();

        downloader.download(url);

    }

}

通过项目入口类我们可以发现，整个项目的细节都在Downloader这个类中，要想弄清楚Downloader类中的细节，我们先把系统工具好好看一看

HttpUtils，主要通过这个工具类获取HTTP请求对象，获取所下载文件的相关信息，如：文件大小、文件名字、分块下载等。

public class HttpUtils {

    
    public static long getHttpFileContentLength(String url) throws IOException {
        int contentLength;
        HttpURLConnection httpURLConnection = null;
        try {
            httpURLConnection = getHttpURLConnection(url);
            contentLength = httpURLConnection.getContentLength();
        } finally {
            if (httpURLConnection != null) {
                httpURLConnection.disconnect();
            }
        }
        return contentLength;
    }

    
    public static HttpURLConnection getHttpURLConnection(String url, long startPos, long endPos) throws IOException {
        HttpURLConnection httpURLConnection = getHttpURLConnection(url);
        LogUtils.info("下载的区间是：{}-{}",startPos,endPos);
        if (endPos != 0) {
            httpURLConnection.setRequestProperty("RANGE","bytes=" + startPos + "-" + endPos);
        }else {
            httpURLConnection.setRequestProperty("RANGE","bytes=" + startPos + "-");
        }
        return httpURLConnection;
    }

    
    public static HttpURLConnection getHttpURLConnection(String url) throws IOException {
        URL httpUrl = new URL(url);
        HttpURLConnection httpURLConnection = (HttpURLConnection) httpUrl.openConnection();
        //向文件所在的服务器发送标识信息
        httpURLConnection.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/14.0.835.163 Safari/535.1");
        return httpURLConnection;
    }

    
    public static String getHttpFileName(String url){
        return url.substring(url.lastIndexOf("/") + 1);
    }

}

FileUtils中的getFileContentLength方法，主要是用来判断该文件有没有重复下载

public class FileUtils {

    
    public static long getFileContentLength(String path){
        File file = new File(path);
        return file.exists() && file.isFile() ? file.length() : 0;
    }

}

LogUtils 自定义日志工具类，提供了统一的日志管理，方便阅读。

public class LogUtils {

    public static void info(String msg,Object... args){
        print(msg,"-info-",args);
    }

    public static void error(String msg,Object... args){
        print(msg,"-error-",args);
    }

    private static void print(String msg,String level,Object... args){
        if (args != null && args.length > 0) {
            msg = String.format(msg.replace("{}","%s"),args);
        }
        String name = Thread.currentThread().getName();;
        System.out.println(LocalTime.now().format(DateTimeFormatter.ofPattern("hh:mm:ss")) + " " +
                name + level + msg);
    }

}

Downloader实现细节

scheduledExecutorService线程池，是用来打印实时的下载信息，比如下载速度什么的。poolExecutor线程池，是用来进行分块下载的，将文件分为多个小块，多个线程并发下载。根据阿里巴巴代码规范手册，最好使用原生方法创建线程池，我这里演示了两种创建方法

public class Downloader {

    private final ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1);

    private final ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(Constant.THREAD_NUM,Constant.THREAD_NUM,
            0,TimeUnit.SECONDS,new ArrayBlockingQueue<>(Constant.THREAD_NUM));

    private final CountDownLatch countDownLatch = new CountDownLatch(Constant.THREAD_NUM);

    public void download(String url){
        //获取文件名
        String httpFileName = HttpUtils.getHttpFileName(url);
        //文件下载路径
        httpFileName = Constant.PATH + httpFileName;

        //获取本地文件大小
        long localFileLength = FileUtils.getFileContentLength(httpFileName);

        HttpURLConnection httpURLConnection = null;
        DownloadInfoThread downloadInfoThread = null;
        //获取连接对象
        try {
            httpURLConnection = HttpUtils.getHttpURLConnection(url);
            //获取下载文件的总大小
            int contentLength = httpURLConnection.getContentLength();
            //文件是否已下载过
            if (localFileLength >= contentLength) {
                LogUtils.info("{}已下载完毕，无需重新下载",httpFileName);
                return;
            }

            //创建获取下载信息的任务对象
            downloadInfoThread = new DownloadInfoThread(contentLength);
            //将任务交给线程池执行，每隔一秒执行一次
            scheduledExecutorService.scheduleAtFixedRate(downloadInfoThread,1,1, TimeUnit.SECONDS);

            //切分对象
            List> list = new ArrayList<>();
            spilt(url,list);

            countDownLatch.await();

            //合并文件
            if (merge(httpFileName)){
                clearTemp(httpFileName);
            }
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.print("r");
            System.out.print("下载完成");
            //关闭对象
            if (httpURLConnection != null) {
                httpURLConnection.disconnect();
            }
            //关闭线程池
            scheduledExecutorService.shutdownNow();
            poolExecutor.shutdown();
        }

    }

    
    public void spilt(String url, List> futureList){
        try {
            //获取下载文件大小
            long contentLength = HttpUtils.getHttpFileContentLength(url);
            //计算切分后的文件大小
            long size = contentLength / Constant.THREAD_NUM;
            //计算分块个数
            for (int i = 0; i < Constant.THREAD_NUM; i++) {
                //计算下载起始位置
                long startPos = i * size;
                //计算结束位置
                long endPos;
                if (i == Constant.THREAD_NUM - 1) {
                    endPos = 0;
                }else {
                    endPos = startPos + size;
                }
                //如果不是第一块，起始位置+1
                if (startPos != 0) {
                    startPos++;
                }

                //创建任务
                DownloaderTask downloaderTask = new DownloaderTask(url, startPos, endPos, i,countDownLatch);

                //提交任务
                Future submit = poolExecutor.submit(downloaderTask);
                futureList.add(submit);
            }
        }catch (IOException e){
            e.printStackTrace();
        }
    }

    
    public boolean merge(String fileName){
        LogUtils.info("开始合并文件{}",fileName);
        byte[] buffer = new byte[Constant.BYTE_SIZE];
        int len = -1;
        try (RandomAccessFile accessFile = new RandomAccessFile(fileName, "rw")){
            for (int i = 0; i < Constant.THREAD_NUM; i++) {
                try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(fileName + ".temp" + i));){
                    while ((len = bis.read(buffer)) != -1) {
                        accessFile.write(buffer,0,len);
                    }
                }
            }
        }catch (Exception e){
            e.printStackTrace();
            return false;
        }
        return true;
    }

    
    public boolean clearTemp(String fileName){
        for (int i = 0; i < Constant.THREAD_NUM; i++) {
            File file = new File(fileName + ".temp" + i);
            file.delete();
        }
        return true;
    }
}

DownloaderTask提交给线程池的任务，也就是分块任务

public class DownloaderTask implements Callable {

    private String url;
    private long startPos;
    private long endPos;
    //分块的块号
    private int part;

    private CountDownLatch countDownLatch;

    public DownloaderTask(String url, long startPos, long endPos, int part, CountDownLatch countDownLatch) {
        this.url = url;
        this.startPos = startPos;
        this.endPos = endPos;
        this.part = part;
        this.countDownLatch = countDownLatch;
    }

    @Override
    public Boolean call() throws Exception {
        //获取文件名
        String httpFileName = HttpUtils.getHttpFileName(url);
        //分块的文件名
        httpFileName = httpFileName + ".temp" + part;
        //下载路径
        httpFileName = Constant.PATH + httpFileName;
        //获取分块下载连接
        HttpURLConnection httpURLConnection = HttpUtils.getHttpURLConnection(url, startPos, endPos);
        try (
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedInputStream bis = new BufferedInputStream(inputStream);
                RandomAccessFile accessFile = new RandomAccessFile(httpFileName, "rw");
        ){
            byte[] buffer = new byte[Constant.BYTE_SIZE];
            int len = -1;
            //循环读取数据
            while ((len = bis.read(buffer)) != -1) {
                //1秒内下载数据之和
                DownloadInfoThread.downSize.add(len);
                accessFile.write(buffer,0,len);
            }
        }catch (FileNotFoundException e){
            LogUtils.error("下载文件不存在{}",url);
            return false;
        }catch (Exception e){
            LogUtils.error("下载出现异常");
            return false;
        }finally {
            httpURLConnection.disconnect();
            countDownLatch.countDown();
        }
        return true;
    }
}

DownloadInfo显示下载信息：

已下载 168.61mb/170.75mb，速度 2320kb/s，剩余时间 0.9s

public class DownloadInfoThread implements Runnable{

    //下载文件总大小
    private long httpFileContentLength;

    //本地已下载文件的大小
    public static LongAdder finishedSize = new LongAdder();

    //本次累计下载的大小
    public static volatile LongAdder downSize = new LongAdder();

    //前一次下载的大小
    public double prevSize;

    public DownloadInfoThread(long httpFileContentLength) {
        this.httpFileContentLength = httpFileContentLength;
    }

    @Override
    public void run() {
        //计算文件总大小 单位：mb
        String httpFileSize = String.format("%.2f",httpFileContentLength / Constant.MB);
        //计算每秒下载速度kb
        int speed = (int)((downSize.doublevalue() - prevSize) / 1024d);
        prevSize = downSize.doublevalue();
        //剩余文件的大小
        double remainSize = httpFileContentLength - finishedSize.doublevalue() - downSize.doublevalue();
        //计算剩余时间
        String remainTime = String.format("%.1f", remainSize / 1024d / speed);
        if ("Infinity".equalsIgnoreCase(remainTime)) {
            remainTime = "-";
        }
        //已下载大小
        String currentFileSize = String.format("%.2f",(downSize.doublevalue() - finishedSize.doublevalue()) / Constant.MB);

        String downInfo = String.format("已下载 %smb/%smb，速度 %skb/s，剩余时间 %ss",
                currentFileSize,httpFileSize,speed,remainTime);

        System.out.print("r");
        System.out.print(downInfo);
    }
}

常量类，便于修改

public class Constant {

    public static final String PATH = "下载文件的存放地址，本地地址";

    public static final double MB = 1024d * 1024d;

    public static final int BYTE_SIZE = 1024 * 100;

    //线程数量
    public static final int THREAD_NUM = 5;
}