spring boot上传文件大小限制原理

柳雅灵 spring, 源码

使用

spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=10MB

以下代码对应spring boot源码版本2.6.5

自动装配

文件上传控制是通过MultipartAutoConfiguration自动装配类装配的

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnClass({Servlet.class, StandardServletMultipartResolver.class, MultipartConfigElement.class})
@ConditionalOnProperty(
    prefix = "spring.servlet.multipart",
    name = {"enabled"},
    matchIfMissing = true
)
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@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 = {"multipartResolver"}
    )
    @ConditionalOnMissingBean({MultipartResolver.class})
    public StandardServletMultipartResolver multipartResolver() {
        StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
        multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
        return multipartResolver;
    }
}

StandardServletMultipartResolver 是一个用于解析 multipart/form-data 数据的标准实现，并且它可以适用于 Servlet 3.0 规范及以上版本。

相比之下，MultipartConfigElement 是一个配置类，它允许您对 servlet 的 multipart/form-data 处理进行更细粒度的控制。通过使用 MultipartConfigElement，您可以指定上传文件的最大大小、缓冲区的大小、临时文件的存储位置等等。这些配置将应用于所有使用该 servlet 的 multipart/form-data 请求。

StandardServletMultipartResolver 用于解析上传的文件，而 MultipartConfigElement 则用于配置如何处理上传的文件。

那么MultipartConfigElement是在哪里被使用的？

dispatcherServlet注册

dispatcherServlet是通过DispatcherServletAutoConfiguration自动装配类装配的

@AutoConfigureOrder(-2147483648)
@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@ConditionalOnClass({DispatcherServlet.class})
@AutoConfigureAfter({ServletWebServerFactoryAutoConfiguration.class})
public class DispatcherServletAutoConfiguration {
    ...
    ...

    @Configuration(
        proxyBeanMethods = false
    )
    @Conditional({DispatcherServletAutoConfiguration.DispatcherServletRegistrationCondition.class})
    @ConditionalOnClass({ServletRegistration.class})
    @EnableConfigurationProperties({WebMvcProperties.class})
    @Import({DispatcherServletAutoConfiguration.DispatcherServletConfiguration.class})
    protected static class DispatcherServletRegistrationConfiguration {
        protected DispatcherServletRegistrationConfiguration() {
        }

        @Bean(
            name = {"dispatcherServletRegistration"}
        )
        @ConditionalOnBean(
            value = {DispatcherServlet.class},
            name = {"dispatcherServlet"}
        )
        public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
            DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet, webMvcProperties.getServlet().getPath());
            registration.setName("dispatcherServlet");
            registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
            multipartConfig.ifAvailable(registration::setMultipartConfig);
            return registration;
        }
    }

    @Configuration(
        proxyBeanMethods = false
    )
    @Conditional({DispatcherServletAutoConfiguration.DefaultDispatcherServletCondition.class})
    @ConditionalOnClass({ServletRegistration.class})
    @EnableConfigurationProperties({WebMvcProperties.class})
    protected static class DispatcherServletConfiguration {
        protected DispatcherServletConfiguration() {
        }

        @Bean(
            name = {"dispatcherServlet"}
        )
        public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
            DispatcherServlet dispatcherServlet = new DispatcherServlet();
            dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
            dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
            dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
            dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
            dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
            return dispatcherServlet;
        }

        @Bean
        @ConditionalOnBean({MultipartResolver.class})
        @ConditionalOnMissingBean(
            name = {"multipartResolver"}
        )
        public MultipartResolver multipartResolver(MultipartResolver resolver) {
            return resolver;
        }
    }
}

可以看到，DispatcherServletConfiguration和DispatcherServletRegistrationConfiguration是这个类的两个内部类。DispatcherServletConfiguration初始化了DispatcherServlet和MultipartResolver两个bean；
DispatcherServletRegistrationConfiguration则是创建了DispatcherServletRegistrationBean，用于注册dispatcherServlet。DispatcherServletRegistrationBean则是通过setMultipartConfig()方法获取了MultipartConfigElement有关文件上传大小控制的配置。

DispatcherServletRegistrationBean继承自->ServletRegistrationBean->DynamicRegistrationBean->RegistrationBean(实现了ServletContextInitializer接口的onStartup方法，注册sevlet到servletContext中)。

ps.ServletContext是Java Servlet规范中的一个接口，它提供了与Web应用程序上下文相关的信息和操作。在Web应用程序启动时，容器（如Tomcat）为每个Web应用程序创建一个ServletContext对象，该对象在整个Web应用程序生命周期内都存在。

堆栈

    org.apache.tomcat.util.http.fileupload.FileUploadBase$SizeLimitExceededException: the request was rejected because its size (47924276) exceeds the configured maximum (10485760)
    at org.apache.tomcat.util.http.fileupload.FileUploadBase$FileItemIteratorImpl.<init>(FileUploadBase.java:811) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.tomcat.util.http.fileupload.FileUploadBase.getItemIterator(FileUploadBase.java:256) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.tomcat.util.http.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:280) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.connector.Request.parseParts(Request.java:2871) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.connector.Request.parseParameters(Request.java:3215) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.connector.Request.getParameter(Request.java:1145) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.connector.RequestFacade.getParameter(RequestFacade.java:381) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:75) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.10.RELEASE.jar:4.3.10.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_131]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_131]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.16.jar:8.5.16]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]

v2-8768ef80ae386008e2603375b38d6f17_720w

另外一个堆栈：
20230510-145931

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