Detailed explanation of the realization of file uploading and downloading under SpringBoot

How to upload and download files in SpringBoot background?

A recent project involves uploading and downloading files. Baidu webUploader plug-in is used for front-end uploading. The usage of this plug-in is still under study, which will be sorted out and recorded in the future. This paper mainly introduces the processing of file uploading and downloading in SpringBoot background.

Single file upload

/  Single file upload 
@RequestMapping(value = "/upload")
@ResponseBody
public String upload(@RequestParam("file") MultipartFile file) {
  try {
  if (file.isEmpty()) {
    return " File is empty ";
  }
  //  Get the file name 
  String fileName = file.getOriginalFilename();
  logger.info(" The uploaded file name is: " + fileName);
  //  Gets the suffix name of the file 
  String suffixName = fileName.substring(fileName.lastIndexOf("."));
  logger.info(" The suffix of the file is: " + suffixName);

  //  Set the file storage path 
  String filePath = "D://aim//";
  String path = filePath + fileName + suffixName;

  File dest = new File(path);
  //  Detect if a directory exists 
  if (!dest.getParentFile().exists()) {
    dest.getParentFile().mkdirs();//  New Folder 
  }
  file.transferTo(dest);//  File writing 
  return " Upload succeeded ";
  } catch (IllegalStateException e) {
    e.printStackTrace();
  } catch (IOException e) {
    e.printStackTrace();
  }
  return " Upload failed ";
}

If you want to modify the file path and file name, modify filePath and fileName.

Multiple file upload

/ Multiple file upload 
@RequestMapping(value = "/uploadMore", method = RequestMethod.POST)
@ResponseBody
public String handleFileUpload(HttpServletRequest request) {
  List<MultipartFile> files = ((MultipartHttpServletRequest) request).getFiles("file");
  MultipartFile file = null;
  BufferedOutputStream stream = null;
  for (int i = 0; i < files.size(); ++i) {
    file = files.get(i);
    String filePath = "D://aim//";
    if (!file.isEmpty()) {
      try {
        byte[] bytes = file.getBytes();
        stream = new BufferedOutputStream(new FileOutputStream(
            new File(filePath + file.getOriginalFilename())));// Set the file path and name 
        stream.write(bytes);//  Write 
        stream.close();
      } catch (Exception e) {
        stream = null;
        return " No. 1  " + i + "  Failed to upload files  ==> "
            + e.getMessage();
      }
    } else {
      return " No. 1  " + i
          + "  Failed to upload files because the file is empty ";
    }
  }
  return " Upload succeeded ";
}

File download

// File download related code 
@RequestMapping("/download")
public String downloadFile(HttpServletRequest request, HttpServletResponse response) {
  String fileName = "aim_test.txt";//  Set the file name and replace it with the file name to be downloaded according to business needs 
  if (fileName != null) {
    // Set the file path 
    String realPath = "D://aim//"
    File file = new File(realPath , fileName);
    if (file.exists()) {
      response.setContentType("application/force-download");//  Setting Force Download Not Open 
      response.addHeader("Content-Disposition", "attachment;fileName=" + fileName);//  Set the file name 
      byte[] buffer = new byte[1024];
      FileInputStream fis = null;
      BufferedInputStream bis = null;
      try {
        fis = new FileInputStream(file);
        bis = new BufferedInputStream(fis);
        OutputStream os = response.getOutputStream();
        int i = bis.read(buffer);
        while (i != -1) {
          os.write(buffer, 0, i);
          i = bis.read(buffer);
        }
        System.out.println("success");
      } catch (Exception e) {
        e.printStackTrace();
      } finally {
        if (bis != null) {
          try {
            bis.close();
          } catch (IOException e) {
            e.printStackTrace();
          }
        }
        if (fis != null) {
          try {
            fis.close();
          } catch (IOException e) {
            e.printStackTrace();
          }
        }
      }
    }
  }
  return null;
}

MultipartConfig Configuration

File uploads can be controlled globally through the MultipartConfig configuration class.

@Configuration
public class MultipartConfig {

  @Bean
  public MultipartConfigElement multipartConfigElement() {
    MultipartConfigFactory factory = new MultipartConfigFactory();
    //  Set file size limit  , Pages beyond this size will throw exception information 
    factory.setMaxFileSize("2MB"); //KB,MB
    //  Set the total uploaded data size 
    factory.setMaxRequestSize("20MB");
    //  Set the file temporary folder path 
    // factory.setLocation("E://test//");
    //  If the file is greater than this value, it will be stored as a file. If it is less than this value, the file will be stored in memory, and the default is 0
    // factory.setMaxRequestSize(0);
    return factory.createMultipartConfig();
  }
}

Matters needing attention

The front and back end file transfer format should be multipart/form-data