错误

当工程升级到SpringBoot2.1使用ServletFileUpload获取Request里面文件报错如下：

org.apache.commons.fileupload.FileUploadBase$InvalidContentTypeException: the request doesn't contain a multipart/form-data or multipart/form-data stream, content type header is null

原因

首先需要了解的是SpringBoot2里自动装配了MultipartResolver

MultipartResolver

来自org.springframework.web.multipart包下的MultipartResolver提供解析包括文件上传在内的多部分请求策略。一种实现方式是基于Commons FileUpload,另外则基于Servlet 3.0的多部分请求解析。

启用多部分处理，需要在DispatcherServletSpring配置中声明一个名为multipartResolver的MultipartResolverbean。DispatcherServlet检测到它并将其应用于传入的请求。当接收到一个content-type是multipart/form-data的POST请求时，解析程序将解析内容并将当前HttpServletRequest包装为MultipartHttpServletRequest，以提供对已解析部分的访问权限，此外将其作为请求参数公开。

而装配MultipartResolver的的配置是MultipartAutoConfiguration

MultipartAutoConfiguration

@Configuration
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class,
		MultipartConfigElement.class })
@ConditionalOnProperty(prefix = "spring.http.multipart", name = "enabled", matchIfMissing = true)
@EnableConfigurationProperties(MultipartProperties.class)
public class MultipartAutoConfiguration {

	private final MultipartProperties multipartProperties;

	public MultipartAutoConfiguration(MultipartProperties multipartProperties) {
		this.multipartProperties = multipartProperties;
	}

	@Bean
	@ConditionalOnMissingBean({ MultipartConfigElement.class,
			CommonsMultipartResolver.class })
	public MultipartConfigElement multipartConfigElement() {
		return this.multipartProperties.createMultipartConfig();
	}

	@Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
	@ConditionalOnMissingBean(MultipartResolver.class)
	public StandardServletMultipartResolver multipartResolver() {
		StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
		multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
		return multipartResolver;
	}

可以看出MultipartAutoConfiguration配置类，默认加载的是StandardServletMultipartResolver。
然而，我们往往会在项目中加入commons-fileupload依赖，加载的是CommonsMultipartResolver。此时同时使用两个，会产生冲突。

解决

1. 启动类排除

在启动类排除配置

@SpringBootApplication(exclude = {MultipartAutoConfiguration.class})

2. 配置文件禁用

spring:
  autoconfigure:
    exclude: org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration

3. 自定义文件解析对象

    @Bean(name = "multipartResolver")
    public MultipartResolver multipartResolver() {
        CommonsMultipartResolver resolver = new CommonsMultipartResolver();
        resolver.setDefaultEncoding("UTF-8");
        return resolver;
    }