byte数组与MultipartFile的相互转化

将byte数组转化为MultipartFile可以通过实现自定义的MultipartFile类来实现，代码如下：

import org.springframework.web.multipart.MultipartFile;
import java.io.*;

public class ByteToMultipartFile implements MultipartFile {

    private final byte[] fileContent;
    private final String fileName;

    public ByteToMultipartFile(byte[] fileContent, String fileName) {
        this.fileContent = fileContent;
        this.fileName = fileName;
    }

    @Override
    public String getName() {
        return null;
    }

    @Override
    public String getOriginalFilename() {
        return fileName;
    }

    @Override
    public String getContentType() {
        return "application/octet-stream";
    }

    @Override
    public boolean isEmpty() {
        return fileContent == null || fileContent.length == 0;
    }

    @Override
    public long getSize() {
        return fileContent.length;
    }

    @Override
    public byte[] getBytes() throws IOException {
        return fileContent;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        return new ByteArrayInputStream(fileContent);
    }

    @Override
    public void transferTo(File dest) throws IOException, IllegalStateException {
        new FileOutputStream(dest).write(fileContent);
    }
}

将MultipartFile转化为byte数组可以通过以下代码实现：

public byte[] multipartFileToByteArray(MultipartFile file) throws IOException {
    return file.getBytes();
}