思路：把MultipartFile先存到项目目录下（或者磁盘），存的时候修改文件名，再读取出来转成MultipartFile

1.实现代码：MultipartFile先存到项目目录，再读取出来File

public static MultipartFile newFileName(MultipartFile multipartFile, String env) {String path = ClassLoader.getSystemResource("").getPath().concat("new_file");if (!"loc".equals(env)) {path = System.getProperty("user.dir") + "/BOOT-INF/classes/new_file/";}log.info("新文件存储路径：{}", path);try {String ext = FileUtil.extName(multipartFile.getOriginalFilename());String fileName = StringHelper.getUUID(16).concat(".").concat(ext);File file = new File(path, fileName);File parentFile = file.getParentFile();if (!parentFile.exists()) {parentFile.mkdir();}multipartFile.transferTo(file);//再把文件读出来if (!file.exists()) {return null;}//把临时海报读取出来MultipartFile mf = FileHelper.file2MultipartFile(file);//把临时文件删除boolean delete = file.delete();log.info("合成海报临时文件删除：{}", delete);return mf;} catch (IOException e) {log.error(e.getLocalizedMessage());}return null;
}

2.实现代码：把File转MultipartFile

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.commons.CommonsMultipartFile;import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;public static MultipartFile file2MultipartFile(File file) {return new CommonsMultipartFile(createFileItem(file));
}private static FileItem createFileItem(File file) {DiskFileItemFactory factory = new DiskFileItemFactory(16, null);FileItem fileItem = factory.createItem("testField", "text/plain", true, file.getName());int byteRead = 0;byte[] buffer = new byte[8192];try (FileInputStream fis = new FileInputStream(file);OutputStream os = fileItem.getOutputStream()) {while ((byteRead = fis.read(buffer, 0, 8192)) != -1) {os.write(buffer, 0, byteRead);}os.close();fis.close();} catch (IOException e) {log.error(e.getLocalizedMessage());}return fileItem;
}