有时候上传文件时，我们会涉及到操作上传文件实体MultipartFile 做一些IO操作，但是有时无法操作文件，只能转换为file才可以。

import org.springframework.web.multipart.MultipartFile;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * @Description:
 * @date 2019/9/23 10:21
 */
public class MultipartFileToFileUtils {

    /**
     * MultipartFile 转 File
     * @param file
     * @throws Exception
     */
    public static File multipartFileToFile(MultipartFile file ) throws Exception {
        File toFile = null;
        if(file.equals("")||file.getSize()<=0){
            file = null;
        }else {
            InputStream ins = null;
            ins = file.getInputStream();
            toFile = new File(file.getOriginalFilename());
            toFile = inputStreamToFile(ins, toFile);
            ins.close();
        }
        return toFile;
    }


    private static File inputStreamToFile(InputStream ins, File file) {
        try {
            OutputStream os = new FileOutputStream(file);
            int bytesRead = 0;
            byte[] buffer = new byte[8192];
            while ((bytesRead = ins.read(buffer, 0, 8192)) != -1) {
                os.write(buffer, 0, bytesRead);
            }
            os.close();
            ins.close();
            return file;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

    /**
     * 图片上传
     *
     * @param file 图片文件
     * @return 图片地址
     */
    @Override
    public String uploadPicture(MultipartFile file) throws Exception {
       //将MultipartFile 转换为File 
        File localFile = MultipartFileToFileUtils.multipartFileToFile(file);
        String imgUrl = uploadUtils.uploadImg(localFile);
        log.info("web upload image url:{}", imgUrl);
        return imgUrl;
    }