1.編寫Spring rest介面，該介面將檔案讀入到流中並通過ResponseEntity物件返回

@RequestMapping(value="/file",method=RequestMethod.GET)
public ResponseEntity<InputStreamResource> getFile(@RequestParam Integer id){
    //設定response返回頭部資訊
    HttpHeaders headers = new HttpHeaders();
    headers.add("Cache-Control", "no-cache, no-store, must-   revalidate"
 
);
    headers.add("Pragma", "no-cache");
    headers.add("Expires", "0");
    FileInputStream input=null;
    File file=null;
    long len=0l;
    try {
    //通過主鍵ID獲取檔案物件
            FileData data=fileMapper.selectByPrimaryKey(id);
            //獲取檔案儲存的路徑
            String filePath=data.getFilePath();
            //通過Paths獲取檔案
 

            file=Paths.get(filePath).toFile();
            input=new FileInputStream(file);
            len=file.length();
        } catch (Exception e) {
            e.printStackTrace();
        }
        //設定返回實體的頭部、長度及型別
        return ResponseEntity
                .ok()
                .headers(headers)
                .contentLength(len)
                .contentType(MediaType.parseMediaType("application/octet-stream"
 
))
                .body(new InputStreamResource(input));

}

2.應用二使用httpclient傳送請求獲取檔案流，然後將檔案流寫入到檔案中實現檔案下載功能

@RequestMapping(value="/file/download/{id}",method=RequestMethod.GET)
public OperationResult downloadFile(@PathVariable(value="id") Integer id,
HttpServletResponse response){
//根據主鍵ID從資料庫中查詢檔案資訊
Map<String,Object> originalDataMap=fileMapper.findFileByPrimaryKey(id);
//獲取檔案的名稱(包含字尾)
String oldFileName=String.valueOf(originalDataMap.get("original_title"));
byte[] buffer= new byte[1024];
        //char[] buffer= new char[1024];
        int len=-1;
        //建立httpClient客戶端
        CloseableHttpClient httpClient=HttpClients.createDefault();
        //建立httpGet傳送請求獲取檔案
        HttpGet httpGet=new HttpGet("http://localhost:8080/test?id="+id);
        //將檔案讀入到輸入流中
        try(CloseableHttpResponse httpResponse=httpClient.execute(httpGet);
                InputStream input=httpResponse.getEntity().getContent();
                OutputStream output=response.getOutputStream();
                ){
            //設定響應頭
            response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(oldFileName, "UTF-8"));       //從輸入流中讀取檔案
            while((len=input.read(buffer))!=-1){
                //將buffer陣列寫入到檔案中，從0開始寫入的長度為實際讀取到的長度len,如果使用write(buffer);會出現中文亂碼及影象變模糊的問題
                output.write(buffer,0,len);
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
}