最近写了一个文件上传的小demo，就是简单的前端html页面，后端controller接收，但是后端一直报错文件为null，看了很多文章，有说spring-boot自带的org.springframework.web.multipart.MultipartFile和Multipart冲突了，要在启动类中加入@EnableAutoConfiguration(exclue={MultipartAutoConfiguration.class})，有说要在MultipartFile参数前加上@RequestParam(“file”)以表明该参数类型是文件类型，还有说是前端表单没有设置enctype=“multipart/form-data”，参照上面方法我还是没有解决问题，后来更换了spring-boot版本就好了，代码如下：

1、pom.xml(注意我这里用的是2.0.4版本)

<?xml version="1.0" encoding="UTF-8"?>

  4.0.0
  
    org.springframework.boot
    spring-boot-starter-parent
    2.0.4.RELEASE
  
  org.sang
  chapter01
  1.0-SNAPSHOT
  
    
      org.springframework.boot
      spring-boot-starter-web
    
  
  
    
      
        org.springframework.boot
        spring-boot-maven-plugin
      
    
  

2、upload.html页面

3、后端controller

import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;
import javax.servlet.http.HttpServletRequest;
import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.UUID;

@RestController
public class FileUploadController {
  SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
  @PostMapping("upload")
  public String upload(MultipartFile uploadFile, HttpServletRequest req){
    String realPath = req.getSession().getServletContext().getRealPath("/uploadFile");
    String format = sdf.format(new Date());
    File folder = new File(realPath+format);
    if(!folder.isDirectory()){
      folder.mkdirs();
    }
    String oldName = uploadFile.getOriginalFilename();
    String newName = UUID.randomUUID().toString()+oldName.substring(oldName.lastIndexOf("."),oldName.length());
    try{
      uploadFile.transferTo(new File(folder,newName));
      String path = req.getScheme()+"://"+req.getServerName()+":"+req.getServerPort()+"/uploadFile/"+format+newName;
      return path;
    }catch (IOException e){
      e.printStackTrace();
    }
    return "上传失败";
  }
}