Spring Boot 文件上传原理解析

  <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">      <property name="defaultEncoding" value="UTF-8"/>      <property name="maxUploadSize" value="100000000"/>      <property name="uploadTempDir" value="fileUpload/temp"/>  </bean>

# multipart config#默认支持文件上传spring.http.multipart.enabled=true#文件上传目录spring.http.multipart.location=/tmp/xunwu/images/#最大支持文件大小spring.http.multipart.max-file-size=4Mb#最大支持请求大小spring.http.multipart.max-request-size=20MB

* Copyright 2002-2017 the original author or authors.package org.springframework.web.multipart.support;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.Part;import org.apache.commons.logging.LogFactory;import org.springframework.web.multipart.MultipartException;import org.springframework.web.multipart.MultipartHttpServletRequest;import org.springframework.web.multipart.MultipartResolver;/** * Standard implementation of the {@link MultipartResolver} interface, * based on the Servlet 3.0 {@link javax.servlet.http.Part} API. * To be added as "multipartResolver" bean to a Spring DispatcherServlet context, * without any extra configuration at the bean level (see below). * * <p><b>Note:</b> In order to use Servlet 3.0 based multipart parsing, * you need to mark the affected servlet with a "multipart-config" section in * {@code web.xml}, or with a {@link javax.servlet.MultipartConfigElement} * in programmatic servlet registration, or (in case of a custom servlet class) * possibly with a {@link javax.servlet.annotation.MultipartConfig} annotation * on your servlet class. Configuration settings such as maximum sizes or * storage locations need to be applied at that servlet registration level; * Servlet 3.0 does not allow for them to be set at the MultipartResolver level. * * @author Juergen Hoeller * @since 3.1 * @see #setResolveLazily * @see HttpServletRequest#getParts() * @see org.springframework.web.multipart.commons.CommonsMultipartResolver */public class StandardServletMultipartResolver implements MultipartResolver {  private boolean resolveLazily = false;  /**   * Set whether to resolve the multipart request lazily at the time of   * file or parameter access.   * <p>Default is "false", resolving the multipart elements immediately, throwing   * corresponding exceptions at the time of the {@link #resolveMultipart} call.   * Switch this to "true" for lazy multipart parsing, throwing parse exceptions   * once the application attempts to obtain multipart files or parameters.   */  public void setResolveLazily(boolean resolveLazily) {    this.resolveLazily = resolveLazily;  }  @Override  public boolean isMultipart(HttpServletRequest request) {    // Same check as in Commons FileUpload...    if (!"post".equals(request.getMethod().toLowerCase())) {      return false;    }    String contentType = request.getContentType();    return (contentType != null && contentType.toLowerCase().startsWith("multipart/"));  }  @Override  public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {    return new StandardMultipartHttpServletRequest(request, this.resolveLazily);  }  @Override  public void cleanupMultipart(MultipartHttpServletRequest request) {    // To be on the safe side: explicitly delete the parts,    // but only actual file parts (for Resin compatibility)    try {      for (Part part : request.getParts()) {        if (request.getFile(part.getName()) != null) {          part.delete();        }      }    }    catch (Throwable ex) {      LogFactory.getLog(getClass()).warn("Failed to perform cleanup of multipart items", ex);    }  }}

package com.bj.config;import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;import org.springframework.boot.autoconfigure.web.MultipartProperties;import org.springframework.boot.context.properties.EnableConfigurationProperties;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.web.multipart.MultipartResolver;import org.springframework.web.multipart.support.StandardServletMultipartResolver;import org.springframework.web.servlet.DispatcherServlet;import javax.servlet.MultipartConfigElement;@Configuration@EnableConfigurationProperties(MultipartProperties.class)public class FileUploadConfig {  private final MultipartProperties multipartProperties;  public FileUploadConfig(MultipartProperties multipartProperties){    this.multipartProperties=multipartProperties;  }  /**   * 注册解析器   * @return   */  @Bean(name= DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)  @ConditionalOnMissingBean(MultipartResolver.class)  public StandardServletMultipartResolver multipartResolver(){    StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();    multipartResolver.setResolveLazily(multipartProperties.isResolveLazily());    return multipartResolver;  }  /**   * 上传配置   * @return   */  @Bean  @ConditionalOnMissingBean  public MultipartConfigElement multipartConfigElement(){    return this.multipartProperties.createMultipartConfig();  }}