4. MultipartAutoConfiguration

前言

MultipartAutoConfiguration 为文件上传进行默认配置。

1、 MultipartConfigElement：ServletWebServerApplicationContext 将 MultipartConfigElementbean 与 Servletbeans 关联起来，MultipartConfigElement 作为 ServletAPI，用于配置如何处理文件上传；

2、 StandardServletMultipartResolver：MultipartResolver 接口的标准实现，基于 Servlet3.0PartAPI，作为默认实现的 springMVC 文件上传解析器组件；

提示：以下是本篇文章正文内容，下面案例可供参考

一、MultipartAutoConfiguration

@Configuration(proxyBeanMethods = false)
//类路径下存在类Servlet, StandardServletMultipartResolver, MultipartConfigElement
@ConditionalOnClass({

      Servlet.class, StandardServletMultipartResolver.class, MultipartConfigElement.class })
//文件上传开关，默认开启
@ConditionalOnProperty(prefix = "spring.servlet.multipart", name = "enabled", matchIfMissing = true)
//servlet web应用环境
@ConditionalOnWebApplication(type = Type.SERVLET)
//文件上传配置信息MultipartProperties
@EnableConfigurationProperties(MultipartProperties.class)
public class MultipartAutoConfiguration {



	private final MultipartProperties multipartProperties;

	public MultipartAutoConfiguration(MultipartProperties multipartProperties) {


		this.multipartProperties = multipartProperties;
	}
	//不存在MultipartConfigElement、CommonsMultipartResolver时创建MultipartConfigElement
	@Bean
	@ConditionalOnMissingBean({

      MultipartConfigElement.class, CommonsMultipartResolver.class })
	public MultipartConfigElement multipartConfigElement() {


		return this.multipartProperties.createMultipartConfig();
	}

	//不存在时创建MultipartResolver
	@Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
	@ConditionalOnMissingBean(MultipartResolver.class)
	public StandardServletMultipartResolver multipartResolver() {


		StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
		multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
		return multipartResolver;
	}

}

示例：pandas 是基于 NumPy 的一种工具，该工具是为了解决数据分析任务而创建的。

二、MultipartProperties

@ConfigurationProperties(prefix = "spring.servlet.multipart", ignoreUnknownFields = false)
public class MultipartProperties {



	/**
	 * Whether to enable support of multipart uploads.
	 */
	 //文件上传开关
	private boolean enabled = true;

	/**
	 * Intermediate location of uploaded files.
	 */
	 //文件上传中间路径
	private String location;

	/**
	 * Max file size.
	 */
	 //文件最大大小
	private DataSize maxFileSize = DataSize.ofMegabytes(1);

	/**
	 * Max request size.
	 */
	 //最大请求文件大小
	private DataSize maxRequestSize = DataSize.ofMegabytes(10);

	/**
	 * Threshold after which files are written to disk.
	 */
	 //阈值，超过后文件将被写入磁盘
	private DataSize fileSizeThreshold = DataSize.ofBytes(0);

	/**
	 * Whether to resolve the multipart request lazily at the time of file or parameter
	 * access.
	 */
	 //延迟解析
	private boolean resolveLazily = false;

	/**
	 * Create a new {@link MultipartConfigElement} using the properties.
	 * @return a new {@link MultipartConfigElement} configured using there properties
	 */
	 //根据默认或自定义配置项创建MultipartConfigElement
	public MultipartConfigElement createMultipartConfig() {


		MultipartConfigFactory factory = new MultipartConfigFactory();
		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
		map.from(this.fileSizeThreshold).to(factory::setFileSizeThreshold);
		map.from(this.location).whenHasText().to(factory::setLocation);
		map.from(this.maxRequestSize).to(factory::setMaxRequestSize);
		map.from(this.maxFileSize).to(factory::setMaxFileSize);
		return factory.createMultipartConfig();
	}

}

常用配置如下

spring.servlet.multipart.enabled=true
spring.servlet.multipart.max-file-size=10485760000
spring.servlet.multipart.max-request-size=52428800000
spring.servlet.multipart.location=d:/tmp

三、 StandardServletMultipartResolver 注册

在 DispatcherServlet 初始化策略过程中，第一步会初始化文件上传解析器

private void initMultipartResolver(ApplicationContext context) {


		try {


			//从spring容器中获取multipartResolver
			this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
			if (logger.isTraceEnabled()) {


				logger.trace("Detected " + this.multipartResolver);
			}
			else if (logger.isDebugEnabled()) {


				logger.debug("Detected " + this.multipartResolver.getClass().getSimpleName());
			}
		}
		catch (NoSuchBeanDefinitionException ex) {


			// Default is no multipart resolver.
			//不存在时赋值为null，不支持文件上传
			this.multipartResolver = null;
			if (logger.isTraceEnabled()) {


				logger.trace("No MultipartResolver '" + MULTIPART_RESOLVER_BEAN_NAME + "' declared");
			}
		}
	}

---