Java中常用的9种文件下载方法总结

目录

• 一、前言
• 二、搭建Spring Boot项目
• 三、文件下载
• 3.1 单文件下载
• 3.2限速下载
• 3.3多文件打成ZIP包下载
• 3.4整个文件夹下载
• 3.5通过URL打包下载
• 3.6导出Excel下载
• 3.7批量导出Excel打包下载
• 3.8多线程加速下载
• 3.9多线程批量导Excel打包下载
• 四、总结

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.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-io</artifactId> <version>1.3.2</version> </dependency> <dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-all</artifactId> <version>5.8.21</version> </dependency> <dependency> <groupId>org.apache.poi</groupId> <artifactId>poi-ooxml</artifactId> <version>4.1.2</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-compress</artifactId> <version>1.20</version> </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<File> 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<String> urls = Arrays.asList("https://demo.com/556.jpeg", "https://demo.com/156.jpeg", "https://demo.com/700.jpeg", "https://demo.com/021.png", "https://demo.com/020.webp", "https://demo.com/972.jpg", "https://demo.com/476.jpeg", "https://demo.com/092.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<List<Integer>> 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<List<Integer>> generateData() { List<List<Integer>> 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<String> urls = Arrays.asList("https://demo.com/144.png", "https://demo.com/824.png", "https://demo.com/928.png", "https://demo.com/800.png", "https://demo.com/480.png", "https://demo.com/232.png", "https://demo.com/528.png", "https://demo.com/737.png", "https://demo.com/736.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。

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