总结常用9种下载（限速、多线程加速、ZIP、导Excel）

公众号：赵侠客

原文：https://mp.weixin.qq.com/s/i49mqqZ9km22gk2A6umaQQ

       一、前言         

下载文件在我们项目很常见，有下载视频、文件、图片、附件、导出Excel、导出Zip压缩文件等等，这里我对常见的下载做个简单的总结，主要有文件下载、限速下载、多文件打包下载、URL文件打包下载、Excel导出下载、Excel批量导出Zip包下载、多线程加速下载。

       二、搭建Spring Boot项目         

搭建个SpringBoot Web项目，引用常用依赖，commons-io作常用IO操作，hutool-all、poi-ooxml做导出Excel操作，commons-compress做多线程压缩。

<dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
        <dependency>
            <groupId>org.apache.commonsgroupId>
            <artifactId>commons-ioartifactId>
            <version>1.3.2version>
        dependency>
        <dependency>
            <groupId>cn.hutoolgroupId>
            <artifactId>hutool-allartifactId>
            <version>5.8.21version>
        dependency>
        <dependency>
            <groupId>org.apache.poigroupId>
            <artifactId>poi-ooxmlartifactId>
            <version>4.1.2version>
        dependency>
        <dependency>
            <groupId>org.apache.commonsgroupId>
            <artifactId>commons-compressartifactId>
            <version>1.20version>
        dependency>

  三、文件下载   

3.1 单文件下载

最简单的下载就是提供一个文件下载接口，浏览器请求接口后预览或者下载文件，这里以下载一个1.2G的视频为例，直接看 /download接口

@GetMapping("/download")
public void download(HttpServletResponse response) throws IOException {
        File file = new File("/Users/zxk/Movies/1.2G.mp4");
        response.setContentType("video/mp4;charset=utf8");
//设置下载文件名
        response.setHeader("Content-Disposition", "attachment;filename=" + file.getName());
//中文乱码处理
//response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(file.getName(), "UTF-8") );
//网页直接播放
//response.setHeader("Content-Disposition", "inline");
//下载进度
        response.setContentLengthLong(file.length());
try (InputStream inputStream = new FileInputStream(file);
             OutputStream outputStream = response.getOutputStream()
        ) {
            IOUtils.copy(inputStream, outputStream);
        }
    }
​

这里有以下几点需要注意：

• 1. response.setContentType设置文件的类型

• 2. Content-Disposition设置文件下载时显示的文件名，如果有中文乱码，需要URLEncode，如果希望浏览器直接打开可以设置"inline"

• 3. response.setContentLengthLong(file.length())，设置Http body长度可以在下载时显示进度

• 4. 下载完成需要关闭流，这里使用try-with-resource自动关闭流

3.2限速下载

使用第一种下载速度会非常快，可能瞬间就将你的服务器带宽占满了，所以就需要限制下载速度。某盘开会员和不开会员下载速度相差非常大，就是针对不用同步给限制了不同的下载速度

@GetMapping("/limitSpeed")
    public void limitSpeed(@RequestParam(value = "speed", defaultValue = "1024") int speed, HttpServletResponse response) throws IOException {
        File path = new File("/Users/zxk/Movies/1.2G.mp4");
        response.setContentType("video/mp4;charset=utf8");
        response.setHeader("Content-Disposition", "attachment;filename=" + path.getName());
        response.setContentLengthLong(path.length());
        try (
                InputStream inputStream = new FileInputStream(path);
                OutputStream outputStream = response.getOutputStream()
        ) {
            byte[] buffer = new byte[1024];
            int length;
            SpeedLimiter speedLimiter = new SpeedLimiter(speed);
            while ((length = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, length);
                speedLimiter.delayNextBytes(length);
            }
        }
    }
​
​
public class SpeedLimiter {
    /** 速度上限(KB/s), 0=不限速 */
    private int maxRate = 1024;
    private long getMaxRateBytes(){
        return this.maxRate * 1024L;
    }
    private long getLessCountBytes() {
        long lcb = getMaxRateBytes() / 10;
        if (lcb < 10240) lcb = 10240;
        return lcb;
    }
    public SpeedLimiter(int maxRate) {
        this.setMaxRate(maxRate);
    }
    public synchronized void setMaxRate(int maxRate){
        this.maxRate = Math.max(maxRate, 0);
    }
    private long totalBytes = 0;
    private long tmpCountBytes = 0;
    private final long lastTime = System.currentTimeMillis();
    public synchronized void delayNextBytes(int len) {
        if (maxRate <= 0) return;
        totalBytes += len;
        tmpCountBytes += len;
        //未达到指定字节数跳过...
        if (tmpCountBytes < getLessCountBytes()) {
            return;
        }
        long nowTime = System.currentTimeMillis();
        long sendTime = nowTime - lastTime;
        long workTime = (totalBytes * 1000) / getMaxRateBytes();
        long delayTime = workTime - sendTime;
        if (delayTime > 0) {
            try {
                Thread.sleep(delayTime);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            tmpCountBytes = 0;
        }
    }
}

3.3多文件打成ZIP包下载

有了单文件下载，肯定就用多文件下载，一般浏览器下载多个文件是将多个文件打包成一个Zip文件下载。

@GetMapping("/zip")
    public void zip(HttpServletResponse response) throws IOException {
        File file1 = new File("/Users/zxk/Movies/2.mp4");
        File file2 = new File("/Users/zxk/Movies/2.mp4");
        List files = Arrays.asList(file2, file1);
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=demo.zip");
        try (ZipOutputStream zipOutputStream = new ZipOutputStream(response.getOutputStream())) {
            zipOutputStream.setLevel(0);
            files.forEach(f -> {
                try (FileInputStream inputStream = new FileInputStream(f)) {
                    zipOutputStream.putNextEntry(new ZipEntry(f.getName()));
                    IOUtils.copy(inputStream, zipOutputStream);
                    zipOutputStream.closeEntry();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
            zipOutputStream.flush();
            zipOutputStream.finish();
        }
    }

多文件打成Zip包注意事项：

• 1. zipOutputStream.setLevel(0)设置压缩等级，0为不压缩，这样可以提升下载速度

• 2. 多个文件打包下载时并不是所有文件压缩完成后才开始下载，而是边压缩边下载，这样用户点了下载后，下载任务会直接进入浏览器下载列表

3.4整个文件夹下载

有时需要递归将整个文件夹打包下载下来

 @GetMapping("/dir")
    public void dir(HttpServletResponse response) throws IOException {
        File dir = new File("/Users/zxk/Movies/download");
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=demo.zip");
        try (ZipOutputStream zipOutputStream = new ZipOutputStream(response.getOutputStream())) {
            zipOutputStream.setLevel(0);
            zip(zipOutputStream, "", dir);
            zipOutputStream.flush();
            zipOutputStream.finish();
        }
    }
​
​
    public void zip(ZipOutputStream zipOutputStream, String parentPath, File file) throws IOException {
        if (file.isDirectory()) {
            File[] subFiles = file.listFiles();
            if (subFiles != null) {
                for (File f : subFiles) {
                    zip(zipOutputStream, parentPath + file.getName() + "/", f);
                }
            }
        } else {
            try (FileInputStream fileInputStream = new FileInputStream(file)) {
                zipOutputStream.putNextEntry(new ZipEntry(parentPath + file.getName()));
                IOUtils.copy(fileInputStream, zipOutputStream);
            }
        }
    }

注意事项：

• 1. 会递归整个文件夹，文件夹文件不能太多

3.5通过URL打包下载

有时我们的文件可能是存在云存储上，数据库里存的是文件的ULR，下载时我们就需要通过URL将多个文件打包下载

    @GetMapping("/urlZip")
    public void urlZip(HttpServletResponse response) throws IOException {
        List urls = Arrays.asList("https://demo.com/11666832527556.jpeg",
                "https://demo.com/11666831385156.jpeg",
                "https://demo.com/11666829917700.jpeg",
                "https://demo.com/11666762702021.png",
                "https://demo.com/11666762702020.webp",
                "https://demo.com/11666549651972.jpg",
                "https://demo.com/11666524497476.jpeg",
                "https://demo.com/11666507113092.jpg");
​
​
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=demo.zip");
        try (ZipOutputStream zipOutputStream = new ZipOutputStream(response.getOutputStream())) {
            zipOutputStream.setLevel(0);
            urls.forEach(f -> {
                try {
                    zipOutputStream.putNextEntry(new ZipEntry(StringUtils.getFilename(f)));
                    HttpUtil.download(f, zipOutputStream, false);
                    zipOutputStream.closeEntry();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
            zipOutputStream.flush();
            zipOutputStream.finish();
        }
    }

3.6导出Excel下载

有些下载的文件并不存在，而是先从数据库中查出数据，再动态生成文件，再提供给用户下载，这里我们以导出单个Excel文件为例：

@GetMapping("/excel")
    public void excel(HttpServletResponse response) throws IOException {
        List> rows = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            rows.add(IntStream.range(i, i + 100).boxed().collect(Collectors.toList()));
        }
        response.setContentType("application/vnd.ms-excel;charset=utf-8");
        response.setHeader("Content-Disposition", "attachment;filename=test.xls");
        try (OutputStream out = response.getOutputStream();
             ExcelWriter writer = ExcelUtil.getWriter()) {
            writer.write(rows);
            writer.flush(out, true);
        }
    }

3.7批量导出Excel打包下载

很多业务需要一次性导出多个Excel，这里我们可以将多个Excel压缩成一个Zip文件下载下来，这里以动态生成10个Excel主例：

    @GetMapping("/excelZip")
    public void excelZip(HttpServletResponse response) throws IOException {
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=demo.zip");
        try (ZipOutputStream zipOutputStream = new ZipOutputStream(response.getOutputStream())) {
            zipOutputStream.setLevel(0);
            for (int i = 0; i < 10; i++) {
                zipOutputStream.putNextEntry(new ZipEntry(String.format("%s.xls", i)));
                try (ExcelWriter writer = ExcelUtil.getWriter()) {
                    writer.write(generateData());
                    writer.flush(zipOutputStream);
                }
            }
            zipOutputStream.flush();
            zipOutputStream.finish();
        }
    }
​
   private List> generateData() {
        List> rows = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            rows.add(IntStream.range(i, i + 100).boxed().collect(Collectors.toList()));
        }
        return rows;
    }

3.8多线程加速下载

有时下载数据量比较多，单线程打包会比较慢，这里我们就需要使用多线程并发打包提高打包速度，这里我以多线程下载多个URL文件为例使用commons-compress的ParallelScatterZipCreator多线程并发打包

public static final ThreadFactory factory = new ThreadFactoryBuilder().setNamePrefix("compressFileList-pool-").build();
  public static final ExecutorService executor = new ThreadPoolExecutor(10, 10, 60, TimeUnit.SECONDS, new LinkedBlockingQueue<>(20), factory);
​
​
​
​
    @GetMapping("/parallelZip")
    public void excelZipThread(HttpServletResponse response) throws IOException {
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=demo.zip");
​
​
​
​
        List urls = Arrays.asList("https://demo.com/11671291835144.png",
        "https://demo.com/11671291834824.png",
        "https://demo.com/11671291833928.png",
        "https://demo.com/11671291833800.png",
        "https://demo.com/11671291833480.png",
        "https://demo.com/11671291828232.png",
        "https://demo.com/11671291827528.png",
        "https://demo.com/11671291825737.png",
        "https://demo.com/11671291825736.png");
​
​
        ParallelScatterZipCreator parallelScatterZipCreator = new ParallelScatterZipCreator(executor);
        try (ZipArchiveOutputStream zipArchiveOutputStream = new ZipArchiveOutputStream(response.getOutputStream())) {
            zipArchiveOutputStream.setLevel(0);
            urls.forEach(x -> {
                ZipArchiveEntry zipArchiveEntry = new ZipArchiveEntry(StringUtils.getFilename(x));
                zipArchiveEntry.setMethod(ZipArchiveEntry.STORED);
                InputStreamSupplier inputStreamSupplier = () -> URLUtil.getStream(URLUtil.url(x));
                parallelScatterZipCreator.addArchiveEntry(zipArchiveEntry, inputStreamSupplier);
            });
            parallelScatterZipCreator.writeTo(zipArchiveOutputStream);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

3.9多线程批量导Excel打包下载

这种是比较复杂的，动态生成多个Excel文件后，使用多线程打成ZIP包下载

    @GetMapping("/parallelexcelZip")
    public void parallelexcelZip(HttpServletResponse response) throws IOException {
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=demo.zip");
        ParallelScatterZipCreator parallelScatterZipCreator = new ParallelScatterZipCreator(executor);
        try (ZipArchiveOutputStream zipArchiveOutputStream = new ZipArchiveOutputStream(response.getOutputStream())) {
            zipArchiveOutputStream.setLevel(0);
            IntStream.range(1,10).forEach(x -> {
                InputStreamSupplier inputStreamSupplier = () ->{
                    ByteArrayOutputStream outputStream=new ByteArrayOutputStream();
                    try(ExcelWriter writer=ExcelUtil.getWriter()) {
                        writer.write(generateData());
                        writer.flush(outputStream);
                    }
                    return  new ByteArrayInputStream(outputStream.toByteArray());
                };
                ZipArchiveEntry zipArchiveEntry = new ZipArchiveEntry(String.format("%s.xls",x));
                zipArchiveEntry.setMethod(ZipArchiveEntry.STORED);
                parallelScatterZipCreator.addArchiveEntry(zipArchiveEntry, inputStreamSupplier);
​
​
            });
            parallelScatterZipCreator.writeTo(zipArchiveOutputStream);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

​​

​   四、总结   

本文主要总结了常用9种常见的文件下载操作，并提供对应的演示代码，当然还有一些没有总结到的，如分片下载、断点结续下、分布式下载限速等，这些高级下载在普通项目中用到的不太多所以没有总结。