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");
}
}
}