实现一个分片下载的工具类, 主要思路就是通过判断请求头中是否包含有range字段, 如果有, 则返回206状态码, 并在响应头中添加Content-Range字段, 否则返回200状态码
1. 分片下载工具类
提供了基于 NIO Channel 和 OutputStream 的两种方式下载文件,
如果请求头没有携带 Range 字段, 则会返回整个文件, Channel的方式也会通过OutputStream下载，这里有需求可以自己更改
package net.lesscoding.utils;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* @author eleven
* @date 2025/4/1 17:11
* @apiNote 分片文件下载工具类
*/
@Component
public class PartialFileDownloadUtil {
// 假设这是文件存储的基础路径，可根据实际情况修改
private static final String FILE_STORAGE_PATH = "D:/__easyHelper__/";
/**
* 使用 NIO 通道下载文件，支持分片下载。
*
* @param fileName 要下载的文件名
* @param request HttpServletRequest 对象，用于获取请求信息
* @param response HttpServletResponse 对象，用于设置响应信息
* @throws IOException 如果在文件操作或网络传输过程中出现错误
*/
public void downloadFileByChannel(String fileName, HttpServletRequest request, HttpServletResponse response) throws IOException {
File file = checkFileIsExists(fileName);
long fileLength = file.length();
String rangeHeader = request.getHeader("Range");
if (rangeHeader != null) {
// 处理 Range 请求
handleRangeRequest(file, rangeHeader, fileLength, response);
} else {
// 完整文件下载
handleFullFileDownload(file, fileLength, response);
}
}
private File checkFileIsExists(String fileName) throws FileNotFoundException {
File file = getFile(fileName);
if (!file.exists()) {
throw new FileNotFoundException("File not found: " + fileName);
}
return file;
}
/**
* 普通方式下载文件，支持分片下载。
*
* @param fileName 要下载的文件名
* @param request HttpServletRequest 对象，用于获取请求信息
* @param response HttpServletResponse 对象，用于设置响应信息
* @throws IOException 如果在文件操作或网络传输过程中出现错误
*/
public void downloadFileByOutputStream(String fileName, HttpServletRequest request, HttpServletResponse response) throws IOException {
File file = checkFileIsExists(fileName);
long fileLength = file.length();
String rangeHeader = request.getHeader("Range");
if (rangeHeader != null) {
// 处理 Range 请求
handleRangeRequestWithRandomAccessFile(file, rangeHeader, fileLength, response);
} else {
// 完整文件下载
handleFullFileDownload(file, fileLength, response);
}
}
/**
* 根据文件名获取文件对象。
* 实际业务中需要换成 OSS 或者 文件服务器 获取
* @param fileName 文件名
* @return 文件对象
*/
private File getFile(String fileName) {
return new File(FILE_STORAGE_PATH + fileName);
}
/**
* 处理 Range 请求，使用 NIO 通道进行文件传输。
*
* @param file 要下载的文件
* @param rangeHeader Range 请求头
* @param fileLength 文件总长度
* @param response HttpServletResponse 对象，用于设置响应信息
* @throws IOException 如果在文件操作或网络传输过程中出现错误
*/
private void handleRangeRequest(File file, String rangeHeader, long fileLength, HttpServletResponse response) throws IOException {
Pattern pattern = Pattern.compile("bytes=(\\d+)-(\\d*)");
Matcher matcher = pattern.matcher(rangeHeader);
if (matcher.matches()) {
long start = Long.parseLong(matcher.group(1));
long end = matcher.group(2).isEmpty() ? fileLength - 1 : Long.parseLong(matcher.group(2));
setPartialContentHeaders(response, start, end, fileLength, file.getName());
try (FileInputStream fis = new FileInputStream(file);
FileChannel fileChannel = fis.getChannel()) {
OutputStream outputStream = response.getOutputStream();
ByteBuffer buffer = ByteBuffer.allocate(4096);
fileChannel.position(start);
long remaining = end - start + 1;
while (remaining > 0) {
int read = fileChannel.read(buffer);
if (read == -1) {
break;
}
buffer.flip();
int length = (int) Math.min(read, remaining);
byte[] bytes = new byte[length];
buffer.get(bytes, 0, length);
outputStream.write(bytes);
buffer.clear();
remaining -= length;
}
}
}
}
/**
* 处理 Range 请求，使用 RandomAccessFile 进行文件传输。
*
* @param file 要下载的文件
* @param rangeHeader Range 请求头
* @param fileLength 文件总长度
* @param response HttpServletResponse 对象，用于设置响应信息
* @throws IOException 如果在文件操作或网络传输过程中出现错误
*/
private void handleRangeRequestWithRandomAccessFile(File file, String rangeHeader, long fileLength, HttpServletResponse response) throws IOException {
Pattern pattern = Pattern.compile("bytes=(\\d+)-(\\d*)");
Matcher matcher = pattern.matcher(rangeHeader);
if (matcher.matches()) {
long start = Long.parseLong(matcher.group(1));
long end = matcher.group(2).isEmpty() ? fileLength - 1 : Long.parseLong(matcher.group(2));
setPartialContentHeaders(response, start, end, fileLength, file.getName());
try (RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r")) {
randomAccessFile.seek(start);
OutputStream outputStream = response.getOutputStream();
byte[] buffer = new byte[4096];
int bytesRead;
long remaining = end - start + 1;
while (remaining > 0 && (bytesRead = randomAccessFile.read(buffer, 0, (int) Math.min(buffer.length, remaining))) != -1) {
outputStream.write(buffer, 0, bytesRead);
remaining -= bytesRead;
}
}
}
}
/**
* 处理完整文件下载。
*
* @param file 要下载的文件
* @param fileLength 文件总长度
* @param response HttpServletResponse 对象，用于设置响应信息
* @throws IOException 如果在文件操作或网络传输过程中出现错误
*/
private void handleFullFileDownload(File file, long fileLength, HttpServletResponse response) throws IOException {
setFullContentHeaders(response, fileLength, file.getName());
try (FileInputStream fis = new FileInputStream(file)) {
OutputStream outputStream = response.getOutputStream();
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = fis.read(buffer)) != -1) {
outputStream.write(buffer, 0, bytesRead);
}
}
}
/**
* 设置完整文件下载的响应头。
*
* @param response HttpServletResponse 对象，用于设置响应信息
* @param fileLength 文件总长度
* @param fileName 文件名
*/
private void setFullContentHeaders(HttpServletResponse response, long fileLength, String fileName) {
response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + fileName + "\"");
response.setHeader(HttpHeaders.CONTENT_LENGTH, String.valueOf(fileLength));
}
/**
* 设置分片下载的响应头。
*
* @param response HttpServletResponse 对象，用于设置响应信息
* @param start 分片开始位置
* @param end 分片结束位置
* @param fileLength 文件总长度
* @param fileName 文件名
*/
private void setPartialContentHeaders(HttpServletResponse response, long start, long end, long fileLength, String fileName) {
response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
response.setHeader(HttpHeaders.CONTENT_RANGE, "bytes " + start + "-" + end + "/" + fileLength);
response.setHeader(HttpHeaders.CONTENT_LENGTH, String.valueOf(end - start + 1));
response.setHeader(HttpHeaders.ACCEPT_RANGES, "bytes");
response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + fileName + "\"");
}
}
