很多时候，在对文件上传和下载的时候，内置的MultipartFile文件类型有时候并不符合我们的操作要求，需要对MultipartFile文件类型进行转换。

/**
 * MultipartFile 转 File
 * @param file
 * @throws Exception
 */
public static void multipartFileToFile( @RequestParam MultipartFile file ) throws Exception {

    File toFile = null;
    if(file.equals("")||file.getSize()<=0){
        file = null;
    }else {
            InputStream ins = null;
            ins = file.getInputStream();
            toFile = new File(file.getOriginalFilename());
            inputStreamToFile(ins, toFile);
            ins.close();
    }

}

/**
 * File 转 MultipartFile
 * @param file
 * @throws Exception
 */
public static void fileToMultipartFile( File file ) throws Exception {

    FileInputStream fileInput = new FileInputStream(file);
    MultipartFile toMultipartFile = new MockMultipartFile("file",file.getName(),"text/plain", IOUtils.toByteArray(fileInput));
    toMultipartFile.getInputStream();

}

/**
 * InputStream 转 File
 * @param ins
 * @param file
 */
public static void inputStreamToFile(InputStream ins, File file) {
    try {
        OutputStream os = new FileOutputStream(file);
        int bytesRead = 0;
        byte[] buffer = new byte[8192];
        while ((bytesRead = ins.read(buffer, 0, 8192)) != -1) {
            os.write(buffer, 0, bytesRead);
        }
        os.close();
        ins.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}