MultipartFile文件上传

引用：https://www.cnblogs.com/896240130Master/p/6430908.html

springmvc 中，文件的上传是通过 MultipartResolver实现的，所以，如果要实现文件的上传，只要在 spring-servlet.xml中注册相应的 MultipartResovler

MultipartResolver实现类：

• CommonsMultipartResolver
• StandardServletMultipartResolver

区别：
第一个需要使用 Apache 的 commons-fileupload 等jar包支持，但能在比较旧的 servlet 版本中使用
第二个不需要第三方jar包支持，他使用servlet内置的上传功能，但只能在servlet3 以上版本使用

引入 CommonsMultipartResolver

在spring-servlet.xml 中 引入 CommonsMultipartResolver 的bean

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="defaultEncoding" value="utf-8"/>
        <property name="maxUploadSize" value="10485760000" />
        <property name="maxInMemorySize" value="40960"/>
</bean>

引入StandardServletMultipartResolver

在spring-servlet.xml 中引入 StandardServletMultipartResolver 的bean

 <bean class="org.springframework.web.multipart.support.StandardServletMultipartResolver" name="multipartResolver">
    </bean>

在 web.xml中 添加 multipart-config 配置

	<servlet>
		<servlet-name>springmvc</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>classpath:spring-servlet.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
		<multipart-config>
<!-- 上传文件的大小限制 5M-->
			<max-file-size>5242880</max-file-size>
<!-- 一次表单提交中文件的大小限制 10M-->
			<max-request-size>10485760</max-request-size>
<!-- 多大的文件会被自动保存到硬盘上， 0 代表所有-->
			<file-size-threshold>0</file-size-threshold>
		</multipart-config>
	</servlet>

代码：
jar包：

 <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.3.1</version>
    </dependency>
    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.5</version>
    </dependency>
    <!-- ServletAPI -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <scope>provided</scope>
    </dependency>

    <!-- SpringMVC -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.2.5.RELEASE</version>
    </dependency>

@RestController
public class HelloController {
    
    @PostMapping("/upload")
    public String hello(HttpServletRequest request){
    
        CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
        System.out.println(multipartResolver.isMultipart(request));
        // 判断是否有文件上传
        if (multipartResolver.isMultipart(request)){
    
            // 获取MultipartHttpServletRequest
            MultipartHttpServletRequest multiRequest = multipartResolver.resolveMultipart(request);
// MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request;
            // 获取request中 所有文件名
            Iterator<String> iterator = multiRequest.getFileNames();
            while (iterator.hasNext()){
    
                MultipartFile file = multiRequest.getFile(iterator.next());

                if (!file.isEmpty()){
    
                    // 上传到这个路径
                    String path = "F:\\images";
                    String fileName = file.getOriginalFilename();
                    String newName = UUID.randomUUID().toString()+fileName.substring(fileName.lastIndexOf("."));
                    File targetFile = new File(path, newName);
                    try {
    
                        file.transferTo(targetFile);
                    } catch (IOException e) {
    
                        e.printStackTrace();
                    }
                }


            }
        }
        return "success";
    }

    @PostMapping("/upload02")
    public String upload(MultipartFile[] files,HttpServletRequest request) throws IOException {
    
        if (files != null && files.length>0){
    
            for (MultipartFile file : files) {
    
                System.out.println("文件流"+file.getInputStream());
                System.out.println("文件字节大小"+file.getSize());
                System.out.println("文件类型"+file.getContentType());
                System.out.println("文件数据:"+file.getBytes());
                System.out.println(file.getName());
                System.out.println(file.getOriginalFilename());

                // servletContext.getRealPath("/")
                String filePath = request.getSession().getServletContext().getRealPath("/")+"assets";
                File dir = new File(filePath);
                if (!dir.exists()){
    
                    dir.mkdirs();
                }
                String fileUrl = filePath +File.separator+ file.getOriginalFilename();
                file.transferTo(new File(fileUrl));
            }
        }



        return "hehe";
    }
}

遇到的问题

• postman发送 带file的请求
  

• MultipartFile 为null
  解决： 1. 没有注入bean ， CommonsMultipartResolver 或者 StandardServletMultipartResolver ,
  2 . 前端传入的名字必须和 MultipartFile 的名字 相同

• request 转 MultipartHttpServletRequest 报错
  解决：multipartResolver.resolveMultipart(request)

   // 获取MultipartHttpServletRequest
    MultipartHttpServletRequest multiRequest = multipartResolver.resolveMultipart(request);
  

  引用：https://blog.csdn.net/MTone1/article/details/83826124

---

springboot中使用 CommonsMultipartResolver

默认引入的是StandardServletMultipartResolver

注入CommonsMultipartResolver

  @Bean
    CommonsMultipartResolver commonsMultipartResolver(){
    
        CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver();
        multipartResolver.setDefaultEncoding("utf-8");
        multipartResolver.setResolveLazily(true);
        multipartResolver.setMaxInMemorySize(40960);
        // 上传文件大小 50M ： 50*1024*1024
        multipartResolver.setMaxUploadSize(50*1024*1024);
        return multipartResolver;
    }