文件上传SpringBoot后端MultipartFile参数报空问题的解决办法

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"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
    </parent>
    <groupId>org.sang</groupId>
    <artifactId>chapter01</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

2、upload.html页面

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="/upload" method="post" enctype="multipart/form-data">
    <input type="file" name="uploadFile" value="请选择文件">
    <input type="submit" value="上传">
</form>
</body>
</html>

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";
    }
}

原文链接：https://blog.csdn.net/u012451819/article/details/109458316