下载文件转换成流，这里说两种流的方式:

1. 文件流

2. 字节流

一，字节流

String filePath=“/opt/peoject/file/123/pdf”; //这个是你服务上存放文件位置

方法体，代码如下：

public byte[] downLoadFile(String filePath) throws Exception {byte[] buffer = null;try {File file = new File(filePath);FileInputStream fis = new FileInputStream(filePath);ByteArrayOutputStream bos = new ByteArrayOutputStream();byte[] b = new byte[1024];int n;while ((n = fis.read(b)) != -1) {bos.write(b, 0, n);}fis.close();bos.close();buffer = bos.toByteArray();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}return buffer;}

后端 controller层：

@PostMapping("/downLoadFile")
public byte[] downLoadFile(HttpServletRequest request,HttpServletResponse response){return  downLoadFile2(response,filePath);
}

前端接收处理、

参考地址：文件下载

二，文件流

public void downLoadFile2(HttpServletResponse response,String filePath) throws Exception {File file = new File(filePath);//获取文件名称 （例如：123.pdf）String fileName=filePath.substring(filePath.lastIndexOf("\\"));InputStream inputStream = new FileInputStream(file);response.setContentType("application/pdf;charset=utf-8");response.setHeader("Content-Disposition", "attachment;filename=\"" + fileName + "\"");IOUtils.copy(inputStream, response.getOutputStream());response.flushBuffer();inputStream.close();}

后端controller

public void downLoadFile(HttpServletRequest request,HttpServletResponse response){downLoadFile2(response,filePath）;
}

下载后，浏览器这里会有显示文件