我有一个下载文件的休息方法。但是，似乎在文件完全复制到输出流之前，下载不会在Web客户端上启动，这对于大型文件可能需要一段时间。
@GetMapping(value = "download-single-report")
public void downloadSingleReport(HttpServletResponse response) {
File dlFile = new File("some_path");
try {
response.setContentType("application/pdf");
response.setHeader("Content-disposition", "attachment; filename="+ dlFile.getName());
InputStream inputStream = new FileInputStream(dlFile);
IOUtils.copy(inputStream, response.getOutputStream());
response.flushBuffer();
} catch (FileNotFoundException e) {
// error
} catch (IOException e) {
// error
}
}
是否有办法“流式传输”文件，以便在我开始写入输出流时立即启动downloda？
我也有一个类似的方法，它接受多个文件并将它们放在一个zip中，将每个zip条目添加到zip流中，并且只有在创建zip后才开始下载：
ZipEntry zipEntry = new ZipEntry(entryName);
zipOutStream.putNextEntry(zipEntry);
IOUtils.copy(fileStream, zipOutStream);
答案 0 :(得分：1)
您可以使用 InputStreamResource 返回流结果。我测试过，它立即开始复制到输出。
@GetMapping(value = "download-single-report")
public ResponseEntity<Resource> downloadSingleReport() {
File dlFile = new File("some_path");
if (!dlFile.exists()) {
return ResponseEntity.notFound().build();
}
try {
try (InputStream stream = new FileInputStream(dlFile)) {
InputStreamResource streamResource = new InputStreamResource(stream);
return ResponseEntity.ok()
.contentType(MediaType.APPLICATION_PDF)
.header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + dlFile.getName() + "\"")
.body(streamResource);
}
/*
// FileSystemResource alternative
FileSystemResource fileSystemResource = new FileSystemResource(dlFile);
return ResponseEntity.ok()
.contentType(MediaType.APPLICATION_PDF)
.header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + dlFile.getName() + "\"")
.body(fileSystemResource);
*/
} catch (IOException e) {
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();
}
}
第二种选择是部分下载方法。
@GetMapping(value = "download-single-report-partial")
public void downloadSingleReportPartial(HttpServletRequest request, HttpServletResponse response) {
File dlFile = new File("some_path");
if (!dlFile.exists()) {
response.setStatus(HttpStatus.NOT_FOUND.value());
return;
}
try {
writeRangeResource(request, response, dlFile);
} catch (Exception ex) {
response.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());
}
}
public static void writeRangeResource(HttpServletRequest request, HttpServletResponse response, File file) throws IOException {
String range = request.getHeader("Range");
if (StringUtils.hasLength(range)) {
//http
ResourceRegion region = getResourceRegion(file, range);
long start = region.getPosition();
long end = start + region.getCount() - 1;
long resourceLength = region.getResource().contentLength();
end = Math.min(end, resourceLength - 1);
long rangeLength = end - start + 1;
response.setStatus(206);
response.addHeader("Accept-Ranges", "bytes");
response.addHeader("Content-Range", String.format("bytes %s-%s/%s", start, end, resourceLength));
response.setContentLengthLong(rangeLength);
try (OutputStream outputStream = response.getOutputStream()) {
try (InputStream inputStream = new BufferedInputStream(new FileInputStream(file))) {
StreamUtils.copyRange(inputStream, outputStream, start, end);
}
}
} else {
response.setStatus(200);
response.addHeader("Accept-Ranges", "bytes");
response.setContentLengthLong(file.length());
try (OutputStream outputStream = response.getOutputStream()) {
try (InputStream inputStream = new BufferedInputStream(new FileInputStream(file))) {
StreamUtils.copy(inputStream, outputStream);
}
}
}
}
private static ResourceRegion getResourceRegion(File file, String range) {
List<HttpRange> httpRanges = HttpRange.parseRanges(range);
if (httpRanges.isEmpty()) {
return new ResourceRegion(new FileSystemResource(file), 0, file.length());
}
return httpRanges.get(0).toResourceRegion(new FileSystemResource(file));
}
Resource 响应由 ResourceHttpMessageConverter 类管理。在 writeContent 方法中，StreamUtils.copy 被调用。
package org.springframework.http.converter;
public class ResourceHttpMessageConverter extends AbstractHttpMessageConverter<Resource> {
..
protected void writeContent(Resource resource, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
try {
InputStream in = resource.getInputStream();
try {
StreamUtils.copy(in, outputMessage.getBody());
}
catch (NullPointerException ex) {
// ignore, see SPR-13620
}
finally {
try {
in.close();
}
catch (Throwable ex) {
// ignore, see SPR-12999
}
}
}
catch (FileNotFoundException ex) {
// ignore, see SPR-12999
}
}
}
out.write(buffer, 0, bytesRead); 立即将数据发送到输出（我已经在本地机器上测试过）。传输整个数据后，会调用 out.flush();。
package org.springframework.util;
public abstract class StreamUtils {
..
public static int copy(InputStream in, OutputStream out) throws IOException {
Assert.notNull(in, "No InputStream specified");
Assert.notNull(out, "No OutputStream specified");
int byteCount = 0;
int bytesRead;
for(byte[] buffer = new byte[4096]; (bytesRead = in.read(buffer)) != -1; byteCount += bytesRead) {
out.write(buffer, 0, bytesRead);
}
out.flush();
return byteCount;
}
}
答案 1 :(得分：0)
使用
IOUtils.copyLarge(InputStream input, OutputStream output)
将字节从大（超过2GB）的InputStream复制到OutputStream。 此方法在内部缓冲输入，因此无需使用BufferedInputStream。
缓冲区大小由DEFAULT_BUFFER_SIZE给出。
或
IOUtils.copyLarge(InputStream input, OutputStream output, byte[] buffer)
将字节从大（超过2GB）的InputStream复制到OutputStream。 此方法使用提供的缓冲区，因此无需使用BufferedInputStream。
http://commons.apache.org/proper/commons-io/javadocs/api-2.4/org/apache/commons/io/IOUtils.html
答案 2 :(得分：0)
您可以使用“StreamingResponseBody” 文件下载将在块写入输出流时立即开始。下面是代码片段
@GetMapping (value = "/download-single-report")
public ResponseEntity<StreamingResponseBody> downloadSingleReport(final HttpServletResponse response) {
final File dlFile = new File("Sample.pdf");
response.setContentType("application/pdf");
response.setHeader(
"Content-Disposition",
"attachment;filename="+ dlFile.getName());
StreamingResponseBody stream = out -> FileCopyUtils.copy(new FileInputStream(dlFile), out);
return new ResponseEntity(stream, HttpStatus.OK);
}