public class FileUtils {

public MultipartFile generateMultipartFile(String fileStr, String fileName, String filePath, Boolean decode) {
		this.getFile(fileStr, filePath, fileName, decode);
		File file = new File(filePath + fileName);
		MultipartFile multipartFile = null;
		try {
			FileInputStream fileInputStream = new FileInputStream(file);
			multipartFile = new MockMultipartFile(file.getName(), fileName, null, fileInputStream);
		} catch (IOException e) {
			log.info("异常信息：" + e);
		}
		return multipartFile;
	}


/**
 * 根据byte数组，生成文件
 */
private void getFile(String fileValue, String filePath, String fileName, Boolean decode) {
    byte[] bfile = Base64.getDecoder().decode(fileValue);
    if(null != decode && !decode){
        bfile = fileValue.getBytes();
    }
    BufferedOutputStream bos = null;
    FileOutputStream fos = null;
    File file = null;
    try {
        File dir = new File(filePath);
        //判断文件目录是否存在
        if (!dir.exists() && !dir.isDirectory()) {
            dir.mkdirs();
        }
        file = new File(filePath + fileName);
        fos = new FileOutputStream(file);
        bos = new BufferedOutputStream(fos);
        bos.write(bfile);
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (bos != null) {
            try {
                bos.close();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }
        if (fos != null) {
            try {
                fos.close();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }
    }
}

}

都有Byte[]了，直接转file