鉴于网上许多下载pdf的代码下载的pdf都是无效pdf，我稍加修改：
@RequestMapping("/downPdf")
public void downPdf(HttpServletResponse response, HttpServletRequest request){
String pdfPath = "C:\\Users\\17921\\Desktop\\spring-boot-reference.pdf";
File file = new File(pdfPath);
String pdfName = FilenameUtils.getName(pdfPath);
OutputStream os = null;
try{
FileInputStream in = new FileInputStream(file);
BufferedInputStream bf = new BufferedInputStream(in);
os = response.getOutputStream();
response.setContentType(MediaType.APPLICATION_PDF_VALUE);
response.setHeader("content-Disposition","attachment;filename="+pdfName);
byte[] b = new byte[bf.available() + 1000];
int i;
while((i=bf.read(b))!=-1){
os.write(b,0,i);
}
os.flush();
}catch(IOException ignored){
}finally {
try {
if (os != null) {
os.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}