Spring Boot实现大文件分片下载
关于文件的上传和下载前面已经讲了2节课，今天我们主要讲一下如何分片下载，历史文章详解下面链接
- Spring Boot实现文件上传和下载
- Spring Boot实现大文件分块上传
1.分片下载的好处
- 使用分片下载： 将大文件分割成多个小块进行下载，可以降低内存占用和网络传输中断的风险。这样可以避免一次性下载整个大文件造成的性能问题。
- 断点续传： 实现断点续传功能，即在下载中途中断后，可以从已下载的部分继续下载，而不需要重新下载整个文件。
- 进度条显示： 在页面上展示下载进度，让用户清晰地看到文件下载的进度。如果一次全部下载可以从process中直接拿到参数计算得出（很精细），如果是分片下载，也是计算已下载的和总大小，只不过已下载的会成片成片的增加（不是很精细）。
分片下载原理
其实和大文件的分片上传原理一样，就是将一个大的文件对象进行切片，然后并发下载分片，最后再进行组装。 只是下载文件需要服务端进行文件的分片，客户端（浏览器）进行文件的组装合并。
HTTP 范围请求
分片下载文件需要用到一个 HTTP 范围请求：
HTTP 协议范围请求允许服务器只发送 HTTP 消息的一部分到客户端。
范围请求在传送大的媒体文件，或者与文件下载的断点续传功能搭配使用时非常有用。如果在响应中存在 Accept-Ranges 首部（并且它的值不为 “none”），那么表示该服务器支持范围请求。 在一个 Range 首部中，可以一次性请求多个部分，服务器会以 multipart 文件的形式将其返回。如果服务器返回的是范围响应，需要使用 206 Partial Content 状态码。假如所请求的范围不合法，那么服务器会返回 416 Range Not Satisfiable 状态码，表示客户端错误。服务器允许忽略 Range 首部，从而返回整个文件，状态码用 200 。
Range 请求语法
Range: =-
Range: =-
Range: =-, -
Range: =-, -, -
unit：范围请求所采用的单位，通常是字节（bytes）。
2.代码工程
实验目的
利用http range实现分片下载
pom.xml
springboot-demo
com.et
1.0-SNAPSHOT
4.0.0
file
8
8
org.springframework.boot
spring-boot-starter-web
org.springframework.boot
spring-boot-autoconfigure
org.springframework.boot
spring-boot-starter-test
test
org.apache.httpcomponents
httpclient
org.apache.httpcomponents
httpmime
org.projectlombok
lombok
cn.hutool
hutool-core
5.8.15
commons-fileupload
commons-fileupload
1.3.1
commons-io
commons-io
2.4
分片下载
package com.et.controller;
import com.et.bean.DownLoadFileInfo;
import org.apache.commons.io.FileUtils;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.concurrent.*;
@RestController
public class DownloadController {
private static final Logger LOGGER = LoggerFactory.getLogger(DownloadController.class);
private final static long PER_PAGE = 1024L * 1024L * 50L;
private final static String DOWN_PATH = "D:\\tmp";
private static final String UTF8 = "UTF-8";
ExecutorService taskExecutor = Executors.newFixedThreadPool(10);
@RequestMapping("/download")
public void downLoadFile(HttpServletRequest request, HttpServletResponse response) throws IOException {
File file = new File("D:\\SoftWare\\oss-browser-win32-ia32.zip");
response.setCharacterEncoding(UTF8);
InputStream is = null;
OutputStream os = null;
try {
// chunk download Range bytes=100-1000 100-
long fSize = file.length();
response.setContentType("application/x-download");
String fileName = URLEncoder.encode(file.getName(), UTF8);
response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
// Accept-Range
response.setHeader("Accept-Range", "bytes");
response.setHeader("fSize", String.valueOf(fSize));
response.setHeader("fName", fileName);
long pos = 0, last = fSize - 1, sum = 0;
if (null != request.getHeader("Range")) {
response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
String numberRange = request.getHeader("Range").replaceAll("bytes=", "");
String[] strRange = numberRange.split("-");
if (strRange.length == 2) {
pos = Long.parseLong(strRange[0].trim());
last = Long.parseLong(strRange[1].trim());
if (last > fSize-1) {
last = fSize - 1;
}
} else {
pos = Long.parseLong(numberRange.replaceAll("-", "").trim());
}
}
long rangeLength = last - pos + 1;
String contentRange = new StringBuffer("bytes").append(pos).append("-").append(last).append("/").append(fSize).toString();
response.setHeader("Content-Range", contentRange);
response.setHeader("Content-Length", String.valueOf(rangeLength));
os = new BufferedOutputStream(response.getOutputStream());
is = new BufferedInputStream(new FileInputStream(file));
is.skip(pos);
byte[] buffer = new byte[1024];
int length = 0;
while (sum < rangeLength) {
int readLength = (int) (rangeLength - sum);
length = is.read(buffer, 0, (rangeLength - sum) <= buffer.length ? readLength : buffer.length);
sum += length;
os.write(buffer,0, length);
}
System.out.println("download finish");
}finally {
if (is != null){
is.close();
}
if (os != null){
os.close();
}
}
}
@RequestMapping("/downloadFile")
public String downloadFile() {
DownLoadFileInfo fileInfo = download(0, 10, -1, null);
if (fileInfo != null) {
long pages = fileInfo.fSize / PER_PAGE;
for (long i = 0; i <= pages; i++) {
Future future = taskExecutor.submit(new DownloadThread(i * PER_PAGE, (i + 1) * PER_PAGE - 1, i, fileInfo.fName));
if (!future.isCancelled()) {
try {
fileInfo = future.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
}
return System.getProperty("user.home") + "\\Downloads\\" + fileInfo.fName;
}
return null;
}
private DownLoadFileInfo download(long start, long end, long page, String fName) {
File dir = new File(DOWN_PATH);
if (!dir.exists()) {
dir.mkdirs();
}
File file = new File(DOWN_PATH, page + "-" + fName);
if (file.exists() && page != -1 && file.length() == PER_PAGE) {
return null;
}
try {
HttpClient client = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://127.0.0.1:8080/download");
httpGet.setHeader("Range", "bytes=" + start + "-" + end);
HttpResponse response = client.execute(httpGet);
String fSize = response.getFirstHeader("fSize").getValue();
fName = URLDecoder.decode(response.getFirstHeader("fName").getValue(), "UTF-8");
HttpEntity entity = response.getEntity();
InputStream is = entity.getContent();
FileOutputStream fos = new FileOutputStream(file);
byte[] buffer = new byte[1024];
int ch;
while ((ch = is.read(buffer)) != -1) {
fos.write(buffer, 0, ch);
}
is.close();
fos.flush();
fos.close();
// last part
if (end - Long.parseLong(fSize) > 0) {
// merge file
mergeFile(fName, page);
}
return new DownLoadFileInfo(Long.parseLong(fSize), fName);
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
private void mergeFile(String fName, long page) {
File file = new File(DOWN_PATH, fName);
try {
BufferedOutputStream os = new BufferedOutputStream(new FileOutputStream(file));
for (long i = 0; i <= page; i++) {
File tempFile = new File(DOWN_PATH, i + "-" + fName);
while (!file.exists() || (i != page && tempFile.length() < PER_PAGE)) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
byte[] bytes = FileUtils.readFileToByteArray(tempFile);
os.write(bytes);
os.flush();
tempFile.delete();
}
File testFile = new File(DOWN_PATH, -1 + "-null");
testFile.delete();
os.flush();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* get file size
*/
private long getRemoteFileSize(String remoteFileUrl) throws IOException {
long fileSize = 0;
HttpURLConnection httpConnection = (HttpURLConnection) new URL(remoteFileUrl).openConnection();
//使用HEAD方法
httpConnection.setRequestMethod("HEAD");
int responseCode = httpConnection.getResponseCode();
if (responseCode >= 400) {
LOGGER.debug("Web responsible fail!");
return 0;
}
String sHeader;
for (int i = 1;; i++) {
sHeader = httpConnection.getHeaderFieldKey(i);
if (sHeader != null && sHeader.equals("Content-Length")) {
LOGGER.debug("file size ContentLength:" + httpConnection.getContentLength());
fileSize = Long.parseLong(httpConnection.getHeaderField(sHeader));
break;
}
}
return fileSize;
}
class DownloadThread implements Callable {
long start;
long end;
long page;
String fName;
public DownloadThread(long start, long end, long page, String fName) {
this.start = start;
this.end = end;
this.page = page;
this.fName = fName;
}
@Override
public DownLoadFileInfo call() {
return download(start, end, page, fName);
}
}
}
以上只是一些关键代码，所有代码请参见下面代码仓库
代码仓库
- GitHub - Harries/springboot-demo: a simple springboot demo with some components for example: redis,solr,rockmq and so on.（File）
3.测试
- 启动Spring Boot应用
- 访问http://127.0.0.1:8080/downloadFile
- 查看日志，发现分为3块下载
download finish
download finish
download finish4.引用
- HTTP Range Request explained
- Spring Boot实现大文件分片下载 | Harries Blog™