java将file转换为MultipartFile，完整代码

完整代码如下：

import org.apache.commons.fileupload.disk.DiskFileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.IOUtils;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.commons.CommonsMultipartFile;

import java.io.File;
import java.io.FileInputStream;
import java.io.OutputStream;
import java.nio.file.Files;

public class FileUtil {

    public static MultipartFile fileToMultipartFile(File file) {
        FileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        FileItem fileItem = new DiskFileItem("file", Files.probeContentType(file.toPath()), false, file.getName(), (int) file.length(), file.getParentFile());
        try {
            FileInputStream inputStream = new FileInputStream(file);
            OutputStream outputStream = fileItem.getOutputStream();
            IOUtils.copy(inputStream, outputStream);
            inputStream.close();
            outputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        MultipartFile multipartFile = new CommonsMultipartFile(fileItem);
        return multipartFile;
    }
}

使用时，只需要调用 fileToMultipartFile(File file) 方法即可将 File 对象转换为 MultipartFile 对象。