File类型转MultipartFile的方法

spring-web自6.0版本后，删除了CommonsMultipartFile类，导致无法使用该类进行转换。

可以使用自定义类进行转换：

定义一个继承MultipartFile的类CustomMultipartFile：

import org.springframework.web.multipart.MultipartFile;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import org.springframework.web.multipart.MultipartFile;

public class CustomMultipartFile implements MultipartFile {
    private final File file;

    public CustomMultipartFile(File file) {
        this.file = file;
    }

    @Override
    public String getName() {
        return file.getName();
    }

    @Override
    public String getOriginalFilename() {
        return file.getName();
    }

    @Override
    public String getContentType() {
        // You may want to implement a better content type detection
        return "application/octet-stream";
    }

    @Override
    public boolean isEmpty() {
        return file.length() == 0;
    }

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

    @Override
    public byte[] getBytes() throws IOException {
        FileInputStream fis = new FileInputStream(file);
        byte[] data = new byte[(int) file.length()];
        fis.read(data);
        fis.close();
        return data;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        return new FileInputStream(file);
    }

    @Override
    public void transferTo(File dest) throws IOException, IllegalStateException {
        // Implement file transfer logic
        Files.copy(file.toPath(), dest.toPath());
    }
}

后续就可以使用CustomMultipartFile类，来将File转换为MultipartFile

File file = new File("path/to/your/file.txt");
CustomMultipartFile customMultipartFile = new CustomMultipartFile(file);