Spring MVC -- 上传文件
Servlet技术出现以前，文件上传的编程仍然是一项很困难的任务，它涉及在服务器端解析原始的HTTP响应。为了减轻编程的痛苦，开发人员借助于商业的文件上传组件。值得庆幸的是，2003年，Apache Software Foundation发布了开源的Commons FileUpload组件，它很快成为了Java Web应用程序员的利器。
经过很多年，Servlet的设计人员才意识到文件文件上传的重要性，并终于成为Servlet 3.0的内置特性。Servlet 3.0的开发人员不再需要将Commons FileUpload组件导入到他们的项目中去。
为此，在Spring MVC中处理文件上传有两种情况：
- 在Servlet 3.0版本以下，使用Apache Commons FileUpload组件；
- 在Servlet 30.版本以上，利用Servlet 3.0及其更高版本的内置支持。
无论使用哪个版本的Servlet，都要利用相同的API来处理已经上传的文件。本篇博客将会介绍如何在需要支持文件上传的Spring MVC应用中使用Commons FileUpload和Servlet 3.0文件上传特性。
一 前端编程
为了上传文件，必须将HTML表格enctype属性值设置为multipart/form-data，像下面这样：
<form action="action" method="post" enctype="multipart/form-data"> select a file <input type="file" name="fieldName"/> <input type="submit" value="Upload"/> </form>
表格中必须包含类型为file的一个input元素，它会显示成一个按钮，单击时，它会打开一个对话框，用来选择文件。
在HTML 5之前，如果想要上传多个文件，必须使用多个类型为file的input元素。但是在HTML 5中，通过在input元素中引入multiple属性，使得多个文件的上传变得更加简单。在HTML 5中编写以下任意一行代码，便可以生成一个按钮来选择多个文件：
<input type="file" name="fieldName" multiple/> <input type="file" name="fieldName" multiple="multiple"/> <input type="file" name="fieldName" multiple=""/>
二 MultipartFile接口
在Spring MVC中处理已经上传的文件十分容易。上传到Spring MVC应用程序中的文件会被包含在一个MultipartFile对象中。我们唯一的任务就是，用类型MultipartFile的属性编写一个domain类。
org.springframework.web.multipart.MultipartFile接口源代码如下：
/* * Copyright 2002-2018 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.web.multipart; import java.io.File; import java.io.IOException; import java.io.InputStream; import java.nio.file.Files; import java.nio.file.Path; import org.springframework.core.io.InputStreamSource; import org.springframework.core.io.Resource; import org.springframework.lang.Nullable; import org.springframework.util.FileCopyUtils; /** * A representation of an uploaded file received in a multipart request. * * <p>The file contents are either stored in memory or temporarily on disk. * In either case, the user is responsible for copying file contents to a * session-level or persistent store as and if desired. The temporary storage * will be cleared at the end of request processing. * * @author Juergen Hoeller * @author Trevor D. Cook * @since 29.09.2003 * @see org.springframework.web.multipart.MultipartHttpServletRequest * @see org.springframework.web.multipart.MultipartResolver */ public interface MultipartFile extends InputStreamSource { /** * Return the name of the parameter in the multipart form. * @return the name of the parameter (never {@code null} or empty) */ String getName(); /** * Return the original filename in the client's filesystem. * <p>This may contain path information depending on the browser used, * but it typically will not with any other than Opera. * @return the original filename, or the empty String if no file has been chosen * in the multipart form, or {@code null} if not defined or not available * @see org.apache.commons.fileupload.FileItem#getName() * @see org.springframework.web.multipart.commons.CommonsMultipartFile#setPreserveFilename */ @Nullable String getOriginalFilename(); /** * Return the content type of the file. * @return the content type, or {@code null} if not defined * (or no file has been chosen in the multipart form) */ @Nullable String getContentType(); /** * Return whether the uploaded file is empty, that is, either no file has * been chosen in the multipart form or the chosen file has no content. */ boolean isEmpty(); /** * Return the size of the file in bytes. * @return the size of the file, or 0 if empty */ long getSize(); /** * Return the contents of the file as an array of bytes. * @return the contents of the file as bytes, or an empty byte array if empty * @throws IOException in case of access errors (if the temporary store fails) */ byte[] getBytes() throws IOException; /** * Return an InputStream to read the contents of the file from. * <p>The user is responsible for closing the returned stream. * @return the contents of the file as stream, or an empty stream if empty * @throws IOException in case of access errors (if the temporary store fails) */ @Override InputStream getInputStream() throws IOException; /** * Return a Resource representation of this MultipartFile. This can be used * as input to the {@code RestTemplate} or the {@code WebClient} to expose * content length and the filename along with the InputStream. * @return this MultipartFile adapted to the Resource contract * @since 5.1 */ default Resource getResource() { return new MultipartFileResource(this); } /** * Transfer the received file to the given destination file. * <p>This may either move the file in the filesystem, copy the file in the * filesystem, or save memory-held contents to the destination file. If the * destination file already exists, it will be deleted first. * <p>If the target file has been moved in the filesystem, this operation * cannot be invoked again afterwards. Therefore, call this method just once * in order to work with any storage mechanism. * <p><b>NOTE:</b> Depending on the underlying provider, temporary storage * may be container-dependent, including the base directory for relative * destinations specified here (e.g. with Servlet 3.0 multipart handling). * For absolute destinations, the target file may get renamed/moved from its * temporary location or newly copied, even if a temporary copy already exists. * @param dest the destination file (typically absolute) * @throws IOException in case of reading or writing errors * @throws IllegalStateException if the file has already been moved * in the filesystem and is not available anymore for another transfer * @see org.apache.commons.fileupload.FileItem#write(File) * @see javax.servlet.http.Part#write(String) */ void transferTo(File dest) throws IOException, IllegalStateException; /** * Transfer the received file to the given destination file. * <p>The default implementation simply copies the file input stream. * @since 5.1 * @see #getInputStream() * @see #transferTo(File) */ default void transferTo(Path dest) throws IOException, IllegalStateException { FileCopyUtils.copy(getInputStream(), Files.newOutputStream(dest)); } }
该接口具有以下方法：
/** * Return the contents of the file as an array of bytes. * @return the contents of the file as bytes, or an empty byte array if empty * @throws IOException in case of access errors (if the temporary store fails) */ byte[] getBytes() throws IOException;
它以字节数组的形式返回文件的内容。
/** * Return the content type of the file. * @return the content type, or {@code null} if not defined * (or no file has been chosen in the multipart form) */ @Nullable String getContentType();
它返回文件的内容类型。
/** * Return an InputStream to read the contents of the file from. * <p>The user is responsible for closing the returned stream. * @return the contents of the file as stream, or an empty stream if empty * @throws IOException in case of access errors (if the temporary store fails) */ @Override InputStream getInputStream() throws IOException;
它返回一个InputStream ，从中读取文件的内容。
/** * Return the name of the parameter in the multipart form. * @return the name of the parameter (never {@code null} or empty) */ String getName();
它以多部分的形式返回参数的名称。
/** * Return the original filename in the client's filesystem. * <p>This may contain path information depending on the browser used, * but it typically will not with any other than Opera. * @return the original filename, or the empty String if no file has been chosen * in the multipart form, or {@code null} if not defined or not available * @see org.apache.commons.fileupload.FileItem#getName() * @see org.springframework.web.multipart.commons.CommonsMultipartFile#setPreserveFilename */ @Nullable String getOriginalFilename();
它返回客户端文件系统中文件的原始文件名称。
/** * Return the size of the file in bytes. * @return the size of the file, or 0 if empty */ long getSize();
它以字节为单位，返回文件的大小。
/** * Transfer the received file to the given destination file. * <p>This may either move the file in the filesystem, copy the file in the * filesystem, or save memory-held contents to the destination file. If the * destination file already exists, it will be deleted first. * <p>If the target file has been moved in the filesystem, this operation * cannot be invoked again afterwards. Therefore, call this method just once * in order to work with any storage mechanism. * <p><b>NOTE:</b> Depending on the underlying provider, temporary storage * may be container-dependent, including the base directory for relative * destinations specified here (e.g. with Servlet 3.0 multipart handling). * For absolute destinations, the target file may get renamed/moved from its * temporary location or newly copied, even if a temporary copy already exists. * @param dest the destination file (typically absolute) * @throws IOException in case of reading or writing errors * @throws IllegalStateException if the file has already been moved * in the filesystem and is not available anymore for another transfer * @see org.apache.commons.fileupload.FileItem#write(File) * @see javax.servlet.http.Part#write(String) */ void transferTo(File dest) throws IOException, IllegalStateException;
它将上传的文件保存到目标目录下。
/** * Return whether the uploaded file is empty, that is, either no file has * been chosen in the multipart form or the chosen file has no content. */ boolean isEmpty();
它表示被上传的文件是否为空（没有上传文件、或者文件内容为空）。
三 使用Commons Fileupload组件上传文件
只有实现了Servlet 3.0及其更高版本规范的Servlet容器，才支持文件上传。对于版本低于Servlet 3.0的容器，则需要Apache Commons Fileupload组件，commons-fileupload.jar包的下载路径如下：https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload。
这是一个开源项目，因此是免费的，它会提供了源代码。为了让Commons Fileupload能够运行，还需要一个Apache Commins组件commons-io.jar，commons-io.jar包的下载路径如下：https://mvnrepository.com/artifact/commons-io/commons-io。
下载完这两个JAR包，我们还需要做以下工作：
- 将这两个JAR文件复制到应用程序的/WEB-INF/lib路径下；
- 在Spring MVC配置文件中定义multipartResolver bean；
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <property name="maxUploadSize" value="5000000000"/> </bean>
CommonsMultipartResolver类，实际上就是将org.apache.commons.fileupload.servlet.ServletFileUpload类和org.apache.commons.fileupload.disk.DiskFileItemFactory的功能进行了整合，具体代码如下：
/* * Copyright 2002-2018 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.web.multipart.commons; import java.util.List; import javax.servlet.ServletContext; import javax.servlet.http.HttpServletRequest; import org.apache.commons.fileupload.FileItem; import org.apache.commons.fileupload.FileItemFactory; import org.apache.commons.fileupload.FileUpload; import org.apache.commons.fileupload.FileUploadBase; import org.apache.commons.fileupload.FileUploadException; import org.apache.commons.fileupload.servlet.ServletFileUpload; import org.springframework.util.Assert; import org.springframework.web.context.ServletContextAware; import org.springframework.web.multipart.MaxUploadSizeExceededException; import org.springframework.web.multipart.MultipartException; import org.springframework.web.multipart.MultipartHttpServletRequest; import org.springframework.web.multipart.MultipartResolver; import org.springframework.web.multipart.support.AbstractMultipartHttpServletRequest; import org.springframework.web.multipart.support.DefaultMultipartHttpServletRequest; import org.springframework.web.util.WebUtils; /** * Servlet-based {@link MultipartResolver} implementation for * <a href="https://commons.apache.org/proper/commons-fileupload">Apache Commons FileUpload</a> * 1.2 or above. * * <p>Provides "maxUploadSize", "maxInMemorySize" and "defaultEncoding" settings as * bean properties (inherited from {@link CommonsFileUploadSupport}). See corresponding * ServletFileUpload / DiskFileItemFactory properties ("sizeMax", "sizeThreshold", * "headerEncoding") for details in terms of defaults and accepted values. * * <p>Saves temporary files to the servlet container's temporary directory. * Needs to be initialized <i>either</i> by an application context <i>or</i> * via the constructor that takes a ServletContext (for standalone usage). * * @author Trevor D. Cook * @author Juergen Hoeller * @since 29.09.2003 * @see #CommonsMultipartResolver(ServletContext) * @see #setResolveLazily * @see org.apache.commons.fileupload.servlet.ServletFileUpload * @see org.apache.commons.fileupload.disk.DiskFileItemFactory */ public class CommonsMultipartResolver extends CommonsFileUploadSupport implements MultipartResolver, ServletContextAware { private boolean resolveLazily = false; /** * Constructor for use as bean. Determines the servlet container's * temporary directory via the ServletContext passed in as through the * ServletContextAware interface (typically by a WebApplicationContext). * @see #setServletContext * @see org.springframework.web.context.ServletContextAware * @see org.springframework.web.context.WebApplicationContext */ public CommonsMultipartResolver() { super(); } /** * Constructor for standalone usage. Determines the servlet container's * temporary directory via the given ServletContext. * @param servletContext the ServletContext to use */ public CommonsMultipartResolver(ServletContext servletContext) { this(); setServletContext(servletContext); } /** * 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; } /** * Initialize the underlying {@code org.apache.commons.fileupload.servlet.ServletFileUpload} * instance. Can be overridden to use a custom subclass, e.g. for testing purposes. * @param fileItemFactory the Commons FileItemFactory to use * @return the new ServletFileUpload instance */ @Override protected FileUpload newFileUpload(FileItemFactory fileItemFactory) { return new ServletFileUpload(fileItemFactory); } @Override public void setServletContext(ServletContext servletContext) { if (!isUploadTempDirSpecified()) { getFileItemFactory().setRepository(WebUtils.getTempDir(servletContext)); } } @Override public boolean isMultipart(HttpServletRequest request) { return ServletFileUpload.isMultipartContent(request); } @Override public MultipartHttpServletRequest resolveMultipart(final HttpServletRequest request) throws MultipartException { Assert.notNull(request, "Request must not be null"); if (this.resolveLazily) { return new DefaultMultipartHttpServletRequest(request) { @Override protected void initializeMultipart() { MultipartParsingResult parsingResult = parseRequest(request); setMultipartFiles(parsingResult.getMultipartFiles()); setMultipartParameters(parsingResult.getMultipartParameters()); setMultipartParameterContentTypes(parsingResult.getMultipartParameterContentTypes()); } }; } else { MultipartParsingResult parsingResult = parseRequest(request); return new DefaultMultipartHttpServletRequest(request, parsingResult.getMultipartFiles(), parsingResult.getMultipartParameters(), parsingResult.getMultipartParameterContentTypes()); } } /** * Parse the given servlet request, resolving its multipart elements. * @param request the request to parse * @return the parsing result * @throws MultipartException if multipart resolution failed. */ protected MultipartParsingResult parseRequest(HttpServletRequest request) throws MultipartException { String encoding = determineEncoding(request); FileUpload fileUpload = prepareFileUpload(encoding); try { List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request); return parseFileItems(fileItems, encoding); } catch (FileUploadBase.SizeLimitExceededException ex) { throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex); } catch (FileUploadBase.FileSizeLimitExceededException ex) { throw new MaxUploadSizeExceededException(fileUpload.getFileSizeMax(), ex); } catch (FileUploadException ex) { throw new MultipartException("Failed to parse multipart servlet request", ex); } } /** * Determine the encoding for the given request. * Can be overridden in subclasses. * <p>The default implementation checks the request encoding, * falling back to the default encoding specified for this resolver. * @param request current HTTP request * @return the encoding for the request (never {@code null}) * @see javax.servlet.ServletRequest#getCharacterEncoding * @see #setDefaultEncoding */ protected String determineEncoding(HttpServletRequest request) { String encoding = request.getCharacterEncoding(); if (encoding == null) { encoding = getDefaultEncoding(); } return encoding; } @Override public void cleanupMultipart(MultipartHttpServletRequest request) { if (!(request instanceof AbstractMultipartHttpServletRequest) || ((AbstractMultipartHttpServletRequest) request).isResolved()) { try { cleanupFileItems(request.getMultiFileMap()); } catch (Throwable ex) { logger.warn("Failed to perform multipart cleanup for servlet request", ex); } } } }
multipartResolver 对象则通过配置property元素来调用setter方法以设置属性值。我们可以通过setter方式注入的属性有：
- maxUploadSize：控制上传单个文件的大小，单位是字节；
- maxInMemorySize：设置上传文件时用到的临时文件的大小，单位是字节；
- defaultEncoding：请求参数的默认编码方式。
这些属性被用来对上传文件进行设置。
此外，CommonsMultipartResolver类的还有一个非常重要的函数：
/** * Parse the given servlet request, resolving its multipart elements. * @param request the request to parse * @return the parsing result * @throws MultipartException if multipart resolution failed. */ protected MultipartParsingResult parseRequest(HttpServletRequest request) throws MultipartException { String encoding = determineEncoding(request); FileUpload fileUpload = prepareFileUpload(encoding); try { List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request); return parseFileItems(fileItems, encoding); } catch (FileUploadBase.SizeLimitExceededException ex) { throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex); } catch (FileUploadBase.FileSizeLimitExceededException ex) { throw new MaxUploadSizeExceededException(fileUpload.getFileSizeMax(), ex); } catch (FileUploadException ex) { throw new MultipartException("Failed to parse multipart servlet request", ex); } }
通过parseRequest()函数解析form中的所有请求字段，并保存到List<FileItem>集合中，然后将集合转换为MultipartParsingResult类型返回：
/** * Holder for a Map of Spring MultipartFiles and a Map of * multipart parameters. */ protected static class MultipartParsingResult { private final MultiValueMap<String, MultipartFile> multipartFiles; private final Map<String, String[]> multipartParameters; private final Map<String, String> multipartParameterContentTypes; public MultipartParsingResult(MultiValueMap<String, MultipartFile> mpFiles, Map<String, String[]> mpParams, Map<String, String> mpParamContentTypes) { this.multipartFiles = mpFiles; this.multipartParameters = mpParams; this.multipartParameterContentTypes = mpParamContentTypes; } public MultiValueMap<String, MultipartFile> getMultipartFiles() { return this.multipartFiles; } public Map<String, String[]> getMultipartParameters() { return this.multipartParameters; } public Map<String, String> getMultipartParameterContentTypes() { return this.multipartParameterContentTypes; } }
MultipartParsingResult类有个重要的属性：
private final MultiValueMap<String, MultipartFile> multipartFiles;
该Map的键值为String类型，保存的是表单类型为file的input元素的name属性值，值为MultipartFile接口类型，该类型保存了该input元素对应的上传文件。
四 Servlet 3.0以下版本文件上传示例
范例upload1展示了如何利用Apache Commons FileUpload处理已经上传的文件。这个范例在Servlet 3.0容器中也是有效的。upload1有一个domain包，包含Procudt类，它包含了一个MultipartFile对象列表。该示例介绍了如何进行产品图片的上传。
1、目录结构
下面展示upload1应用的目录结构：
注意：在lib中我们需要导入Apache Commons FileUpload组件。
2、Product类
Product类具有类型为List<MultipartFile>的imagea属性，这个属性用来保存上传的产品图片文件（可以是多个图片文件）：
package domain; import java.io.Serializable; import java.math.BigDecimal; import java.util.List; import javax.validation.constraints.NotNull; import javax.validation.constraints.Size; import org.springframework.web.multipart.MultipartFile; public class Product implements Serializable { private static final long serialVersionUID = 1; @NotNull @Size(min=1, max=10) private String name; private String description; private BigDecimal price; private List<MultipartFile> images; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public BigDecimal getPrice() { return price; } public void setPrice(BigDecimal price) { this.price = price; } public List<MultipartFile> getImages() { return images; } public void setImages(List<MultipartFile> images) { this.images = images; } }
3、控制器
package controller; import java.io.File; import java.io.IOException; import java.util.ArrayList; import java.util.List; import javax.servlet.http.HttpServletRequest; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.stereotype.Controller; import org.springframework.ui.Model; import org.springframework.validation.BindingResult; import org.springframework.web.bind.annotation.ModelAttribute; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.multipart.MultipartFile; import domain.Product; @Controller public class ProductController { private static final Log logger = LogFactory .getLog(ProductController.class); //请求URL：/input-product @RequestMapping(value = "/input-product") public String inputProduct(Model model) { model.addAttribute("product", new Product()); return "ProductForm"; } //请求URL：/save-product @RequestMapping(value = "/save-product") public String saveProduct(HttpServletRequest servletRequest, @ModelAttribute Product product, BindingResult bindingResult, Model model) { //获取上传的图片文件(可以多个文件) List<MultipartFile> files = product.getImages(); //用于保存所有文件名 List<String> fileNames = new ArrayList<String>(); //检验是否有文件？ if (null != files && files.size() > 0) { //遍历 for (MultipartFile multipartFile : files) { //获取文件名 String fileName = multipartFile.getOriginalFilename(); fileNames.add(fileName); //获取应用/image虚拟路径在文件系统上对应的真实路径 + 文件名 并创建File对象 File imageFile = new File(servletRequest.getServletContext() .getRealPath("/image"), fileName); try { //将上传的文件保存到目标目录下 multipartFile.transferTo(imageFile); } catch (IOException e) { e.printStackTrace(); } } } // save product here model.addAttribute("product", product); return "ProductDetails"; } }
ProductController类有inputProduct()和saveProduct()两个请求处理方法。inputProduct()方法向浏览器发出一个产品表单，saveProduct()方法将已经上传的图片文件保存到应用程序的image目录下，文件名不改变。
注意：必须先创建好image文件夹。
4、配置文件
下面给出springmvc-config.xml文件的所有内容：
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="controller" /> <mvc:annotation-driven /> <mvc:resources mapping="/css/**" location="/css/" /> <mvc:resources mapping="/*.html" location="/" /> <mvc:resources mapping="/image/**" location="/image/" /> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/" /> <property name="suffix" value=".jsp" /> </bean> <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <property name="maxUploadSize" value="5000000000"/> </bean> </beans>
利用multipartResolver bean的maxUploadSize属性，可以设置能够接受的最大文件容量。如果没有设置这个属性，则没有最大文件容量限制。没有设置文件容量限制，并不意味着可以上传任意大小的文件。上传过大的文件时需要花费很长的时间，这样会导致服务器超时，为了处理超大文件的问题，可以利用HTML 5 File API将文件切片，然后再分别上传这些文件。
如果想对上传的文件类型进行过滤，那么我们可以需要先获取上传文件的名称，然后检测其扩展名。此外，我们也可以在前端使用js代码检测上传文件的扩展名。
部署描述符(web.xml文件)：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"> <!-- 配置编码方式过滤器,注意一点:要配置在所有过滤器的前面 --> <filter> <filter-name>CharacterEncodingFilter</filter-name> <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class> <init-param> <param-name>encoding</param-name> <param-value>utf-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>CharacterEncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <servlet> <servlet-name>springmvc</servlet-name> <servlet-class> org.springframework.web.servlet.DispatcherServlet </servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/config/springmvc-config.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>springmvc</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app>
注意，web.xml文件中我们配置了编码方式过滤器，将所有http请求的参数编码为UTF-8方式，与jsp中页面编码一致。
5、视图
用于上传图片文件的ProductForm.jsp页面如下所示：
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %> <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <title>Add Product Form</title> <style type="text/css">@import url("<c:url value="/css/main.css"/>");</style> </head> <body> <div id="global"> <form:form modelAttribute="product" action="save-product" method="post" enctype="multipart/form-data"> <fieldset> <legend>Add a product</legend> <p> <label for="name">Product Name: </label> <form:input id="name" path="name" cssErrorClass="error"/> <form:errors path="name" cssClass="error"/> </p> <p> <label for="description">Description: </label> <form:input id="description" path="description"/> </p> <p> <label for="price">Price: </label> <form:input id="price" path="price" cssErrorClass="error"/> </p> <p> <label for="image">Product Image: </label> <input type="file" name="images[0]"/> </p> <p id="buttons"> <input id="reset" type="reset" tabindex="4"> <input id="submit" type="submit" tabindex="5" value="Add Product"> </p> </fieldset> </form:form> </div> </body> </html>
注意表单中类型为file的input元素，它将显示为一个按钮，用于选择要上传的文件。并且input元素的name属性指定为"images[0]"，即绑定到表单支持对象product的images属性（List<MultipartFile>类型>）的第一个元素上。
如果想支持多个文件同时上传，只需将 <input type="file" name="images[0]"/>替换成如下：
<input type="file" name="images" multiple/>
提交Product表单，将会调用saveProduct()方法，如果这个方法能够顺利执行，用户将会跳转到ProductDetails.jsp页面：
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <title>Save Product</title> <style type="text/css">@import url("<c:url value="/css/main.css"/>");</style> </head> <body> <div id="global"> <h4>The product has been saved.</h4> <p> <h5>Details:</h5> Product Name: ${product.name}<br/> Description: ${product.description}<br/> Price: $${product.price} <p>Following files are uploaded successfully.</p> <ol> <c:forEach items="${product.images}" var="image"> <li>${image.originalFilename} <img width="100" src="<c:url value="/image/"/> ${image.originalFilename}"/> </li> </c:forEach> </ol> </p> </div> </body> </html>
该页面将会显示已经保存的Product的详细信息及其图片。
6、测试
将应用程序部署到tomcat服务器，并在网页输入以下URL：
http://localhost:8008/upload1/input-product
将会看到一个如图所示的Add Product表单，试着输入一些产品信息，并选择一个要上传的文件：
单击"Add Product"按钮，就可以看到如下所示的网页：
同时我们可以在tomcat服务器，upload1应用下的image目录下看到，已经上传的文件：
如果将ProductForm.jsp中的：<input type="file" name="images[0]"/>更改为如下代码：
<input type="file" name="images" multiple/>
那么就可以实现多个文件同时上传：
五 Servlet 3.0及其更高版本上传文件
有了Servlet 3.0就不需要Common FileUpload和Common IO JAR包了。在Servlet 3.0及其以上版本的容器进行服务器端文件上传的编程，是围绕着注解类型MultipartConfig和javax.servlet.http.Part接口进行的。处理已上传文件的Servlets必须以@MultipartConfig进行注解。
下列是可能在MultipartConfig注解类型中出现的属性，它们都是可选的：
- maxFileSize：单个上传文件的最大容量，默认值是-1，表示没有限制，大于指定容量的文件将会遭到拒绝；
- maxRequestSize：表示Multipart HTTP请求运行的最大容量，默认值为-1，表示没有限制；
- location：表示在Part调用write()方法时，要将已上传的文件保存到磁盘中的位置；
- fileSizeThreshod：设置上传文件时用到的临时文件的大小；
Spring MVC的DispatcherServlet处理大部分或者所有请求。但是遗憾的是，如果不修改源代码，将无法对Servlet进行注解。但值得庆幸的是，Servlet 3.0中有一种比较容易的方法，能使一个Servlet变成一个MultipartConfig Servlet，即给部署描述符(web.xml)中的Servlet声明赋值。以下代码与用@MultipartConfig给DispatcherServlet进行注解的效果一样：
<servlet> <servlet-name>springmvc</servlet-name> <servlet-class> org.springframework.web.servlet.DispatcherServlet </servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/config/springmvc-config.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> <multipart-config> <max-file-size>20848820</max-file-size> <max-request-size>418018841</max-request-size> <file-size-threshold>1048576</file-size-threshold> </multipart-config> </servlet>
此外，还需要在Spring MVC配置文件中使用一个StandardServletMultipartResolver，如下：
<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"> </bean>
upload2应用程序展示了如何在Servlet 3.0以及更改版本的容器中处理文件上传问题，这是从upload1中改写过来的，upload2和upload1相似部分不再做详细介绍。主要的区别在于，现在的web.xml文件中包含了一个multipart-config元素。upload2应用的目录结构如下：
1、配置文件
下面是upload2应用的部署描述符(web.xml文件)：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"> <servlet> <servlet-name>springmvc</servlet-name> <servlet-class> org.springframework.web.servlet.DispatcherServlet </servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/config/springmvc-config.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> <multipart-config> <max-file-size>20848820</max-file-size> <max-request-size>418018841</max-request-size> <file-size-threshold>1048576</file-size-threshold> </multipart-config> </servlet> <servlet-mapping> <servlet-name>springmvc</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app>
Spring MVC配置文件：
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="controller" /> <mvc:annotation-driven /> <mvc:resources mapping="/css/**" location="/css/" /> <mvc:resources mapping="/*.html" location="/" /> <mvc:resources mapping="/image/**" location="/image/" /> <mvc:resources mapping="/file/**" location="/file/" /> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/" /> <property name="suffix" value=".jsp" /> </bean> <bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"> </bean> </beans>
2、Produtct类
package domain; import java.io.Serializable; import java.math.BigDecimal; import java.util.List; import javax.validation.constraints.NotNull; import javax.validation.constraints.Size; import org.springframework.web.multipart.MultipartFile; public class Product implements Serializable { private static final long serialVersionUID = 78L; @NotNull @Size(min=1, max=10) private String name; private String description; private BigDecimal price; private List<MultipartFile> images; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public BigDecimal getPrice() { return price; } public void setPrice(BigDecimal price) { this.price = price; } public List<MultipartFile> getImages() { return images; } public void setImages(List<MultipartFile> images) { this.images = images; } }
3、ProductController类
package controller; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.List; import javax.servlet.http.HttpServletRequest; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.stereotype.Controller; import org.springframework.ui.Model; import org.springframework.validation.BindingResult; import org.springframework.validation.FieldError; import org.springframework.web.bind.annotation.ModelAttribute; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.multipart.MultipartFile; import domain.Product; @Controller public class ProductController { private static final Log logger = LogFactory.getLog(ProductController.class); //请求URL：/input-product @RequestMapping(value="/input-product") public String inputProduct(Model model) { model.addAttribute("product", new Product()); return "ProductForm"; } //请求URL：/save-product @RequestMapping(value = "/save-product") public String saveProduct(HttpServletRequest servletRequest, @ModelAttribute Product product, BindingResult bindingResult, Model model) { //获取上传的图片文件(可以多个文件) List<MultipartFile> files = product.getImages(); //用于保存所有文件名 List<String> fileNames = new ArrayList<String>(); //检验是否有文件？ if (null != files && files.size() > 0) { //遍历 for (MultipartFile multipartFile : files) { //获取文件名 String fileName = multipartFile.getOriginalFilename(); fileNames.add(fileName); //获取应用/image虚拟路径在文件系统上对应的真实路径 + 文件名 并创建File对象 File imageFile = new File(servletRequest.getServletContext() .getRealPath("/image"), fileName); try { //将上传的文件保存到目标目录下 multipartFile.transferTo(imageFile); } catch (IOException e) { e.printStackTrace(); } } } // save product here model.addAttribute("product", product); return "ProductDetails"; } }
4、视图
ProductForm.jsp：
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %> <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <!DOCTYPE html> <html> <head> <title>Add Product Form</title> <style type="text/css">@import url("<c:url value="/css/main.css"/>");</style> </head> <body> <div id="global"> <form:form modelAttribute="product" action="save-product" method="post" enctype="multipart/form-data"> <fieldset> <legend>Add a product</legend> <p> <label for="name">Product Name: </label> <form:input id="name" path="name" cssErrorClass="error"/> <form:errors path="name" cssClass="error"/> </p> <p> <label for="description">Description: </label> <form:input id="description" path="description"/> </p> <p> <label for="price">Price: </label> <form:input id="price" path="price" cssErrorClass="error"/> </p> <p> <label for="image">Product Image: </label> <!-- <input type="file" name="images[0]"/> --> <input type="file" name="images" multiple/> </p> <p id="buttons"> <input id="reset" type="reset" tabindex="4"> <input id="submit" type="submit" tabindex="5" value="Add Product"> </p> </fieldset> </form:form> </div> </body> </html>
ProductDetails：
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <!DOCTYPE html> <html> <head> <title>Save Product</title> <style type="text/css">@import url("<c:url value="/css/main.css"/>");</style> </head> <body> <div id="global"> <h4>The product has been saved.</h4> <p> <h5>Details:</h5> Product Name: ${product.name}<br/> Description: ${product.description}<br/> Price: $${product.price} <p>Following files are uploaded successfully.</p> <ol> <c:forEach items="${product.images}" var="image"> <li>${image.originalFilename} <img width="100" src="<c:url value="/image/"/>${image.originalFilename}"/> </li> </c:forEach> </ol> </p> </div> </body> </html>
main.css：
#global { text-align: left; border: 1px solid #dedede; background: #efefef; width: 560px; padding: 20px; margin: 30px auto; } form { font:100% verdana; min-width: 500px; max-width: 600px; width: 560px; } form fieldset { border-color: #bdbebf; border-width: 3px; margin: 0; } legend { font-size: 1.3em; } form label { width: 250px; display: block; float: left; text-align: right; padding: 2px; } #buttons { text-align: right; } #errors, li { color: red; } .error { color: red; font-size: 9pt; }
5、测试
将应用程序部署到tomcat服务器，并在网页输入以下URL：
http://localhost:8008/upload2/input-product
将会看到一个如图所示的Add Product表单，试着输入一些产品信息，并选择一个要上传的文件：
单击"Add Product"按钮，就可以看到如下所示的网页：
六 upload2应用HTML 5进行文件上传
虽然Servlet 3.0中的文件上传特性使文件上传变得十分容器，只需在服务器端编程即可，但是这对提升用户体验毫无帮助。单独一个HTML表单并不能显示进度条，或者显示已经成功上传的文件数量。开发人员采用了各种不同的技术来改善用户界面，例如，单独用一个浏览器线程对服务器发出请求，以便报告上传进度，或者利用像Java applets、Adobe Flash、Microsoft Silverlight这样的第三方技术。
这些第三方技术可以工作，但都在一定程度上存在限制。今天Java applets和Microsoft Silverlight几乎过时了，Chrome不在允许Java applets和Microsoft Silverlight，Microsoft取代Internet Explorer的新浏览器Edge根本不需要插件。
我们仍然可以使用Flash、因为Chrome仍然可以运行它，Edge已经集成了它，然而，现在越来越多的人选择使用HTML 5。
HTML 5在其DOM中添加了一个File API，它允许访问本地文件。与Java applets、Adobe Flash、Microsoft Silverlight相比，HTML 5似乎是针对客户端文件上传局限性的最佳解决方案。
为了验证HTML 5的性能，upload2中的html5页面采用了JavaScript和HTML 5 File API来提供报告上传进度的进度条。upload2应用程序中也创建了一个UploadedFile 类，用于在服务器中保存已上传的文件。
1、UploadedFile类
upload2的UploadedFile类只包含一个属性multipartFile，用来保存已经上传的文件：
package domain; import java.io.Serializable; import org.springframework.web.multipart.MultipartFile; public class UploadedFile implements Serializable { private static final long serialVersionUID = 1L; //用来保存已经上传的文件 private MultipartFile multipartFile; public MultipartFile getMultipartFile() { return multipartFile; } public void setMultipartFile(MultipartFile multipartFile) { this.multipartFile = multipartFile; } }
2、Html5FileUploadController类
upload2中的Html5FileUploadController类能够将已经上传的文件保存到应用程序的file目录下：
package controller; import java.io.File; import java.io.IOException; import javax.servlet.http.HttpServletRequest; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.stereotype.Controller; import org.springframework.ui.Model; import org.springframework.validation.BindingResult; import org.springframework.web.bind.annotation.ModelAttribute; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.multipart.MultipartFile; import domain.UploadedFile; @Controller public class Html5FileUploadController { private static final Log logger = LogFactory .getLog(Html5FileUploadController.class); //请求URL:/html5 @RequestMapping(value = "/html5") public String inputProduct() { return "Html5"; } //请求URL:/upload-file @RequestMapping(value = "/upload-file") public void saveFile(HttpServletRequest servletRequest, @ModelAttribute UploadedFile uploadedFile, BindingResult bindingResult, Model model) { //获取已经上传的文件 MultipartFile multipartFile = uploadedFile.getMultipartFile(); //获取上传的文件名 String fileName = multipartFile.getOriginalFilename(); try { //获取应用/file虚拟路径在文件系统上对应的真实路径 + 文件名 并创建File对象 File file = new File(servletRequest.getServletContext() .getRealPath("/file"), fileName); //将上传的文件保存到目标目录下 multipartFile.transferTo(file); } catch (IOException e) { e.printStackTrace(); } } }
3、html5.jsp页面
<!DOCTYPE html> <html> <head> <script> var totalFileLength, totalUploaded, fileCount, filesUploaded; // show uoload file information use element of id="debug" function debug(s) { var debug = document.getElementById('debug'); if (debug) { debug.innerHTML = debug.innerHTML + '<br/>' + s; } } //load event of XMLHttpRequest object function onUploadComplete(e) { totalUploaded += document.getElementById('files'). files[filesUploaded].size; filesUploaded++; debug('complete ' + filesUploaded + " of " + fileCount); debug('totalUploaded: ' + totalUploaded); if (filesUploaded < fileCount) { uploadNext(); } else { var bar = document.getElementById('bar'); bar.style.width = '100%'; bar.innerHTML = '100% complete'; alert('Finished uploading file(s)'); } } //trigger when selecting file change function onFileSelect(e) { var files = e.target.files; // FileList object var output = []; //get upload file count fileCount = files.length; totalFileLength = 0; for (var i=0; i<fileCount; i++) { var file = files[i]; output.push(file.name, ' (', file.size, ' bytes, ', file.lastModifiedDate.toLocaleDateString(), ') ' ); output.push('<br/>'); debug('add ' + file.name + ' ('+ file.size + 'bytes' + ') ' ); totalFileLength += file.size; } //show selecting file information document.getElementById('selectedFiles').innerHTML = output.join(''); debug('totalFileLength: ' + totalFileLength + 'bytes'); } //progress event of XMLHttpRequest object function onUploadProgress(e) { if (e.lengthComputable) { var percentComplete = parseInt( (e.loaded + totalUploaded) * 100 / totalFileLength); var bar = document.getElementById('bar'); bar.style.width = percentComplete + '%'; bar.innerHTML = percentComplete + ' % complete'; } else { debug('unable to compute'); } } //error event of XMLHttpRequest object function onUploadFailed(e) { alert("Error uploading file"); } //upload next file function uploadNext() { var xhr = new XMLHttpRequest(); var fd = new FormData(); var file = document.getElementById('files'). files[filesUploaded]; fd.append("multipartFile", file); xhr.upload.addEventListener( "progress", onUploadProgress, false); xhr.addEventListener("load", onUploadComplete, false); xhr.addEventListener("error", onUploadFailed, false); xhr.open("POST", "upload-file"); debug('uploading ' + file.name); xhr.send(fd); } //trigger when click Upload button function startUpload() { totalUploaded = filesUploaded = 0; uploadNext(); } //trigger when window load window.onload = function() { document.getElementById('files').addEventListener( 'change', onFileSelect, false); document.getElementById('uploadButton'). addEventListener('click', startUpload, false); } </script> </head> <body> <h1>Multiple file uploads with progress bar</h1> <div id='progressBar' style='height:20px;border:2px solid green'> <div id='bar' style='height:100%;background:#33dd33;width:0%'> </div> </div> <form> <input type="file" id="files" multiple/> <br/> <output id="selectedFiles"></output> <input id="uploadButton" type="button" value="Upload"/> </form> <div id='debug' style='height:300px;border:2px solid green;overflow:auto'> </div> </body> </html>
html5.jsp页面主要包含以下三部分：
- 一个id为progressBar的div元素：用于展示上传进度；
- 一个表单：表单中有一个类型为file的input元素和一个按钮，用于上传文件；
- 一个id为debug的div元素，用来显示调试信息，主要包括上传文件信息；
这个表单有两点需要注意：
<form> <input type="file" id="files" multiple/> <br/> <output id="selectedFiles"></output> <input id="uploadButton" type="button" value="Upload"/> </form>
- id为files的input元素，它有一个multiple属性，用于支持多文件选择；
- 这个按钮不是一个提交按钮，因此单击它不会提交表单，事实上，脚本是利用XMLHttpRequest对象来上传的；
下面来看JavaScript代码。执行脚本时，它做的第一件事就是为这4个变量分配空间：
var totalFileLength, totalUploaded, fileCount, filesUploaded;
(1) totalFileLength变量保存要上传的文件总长度；
(2) totalUploaded是指目前已经上传的字节数；
(3) fileCount：要上传的文件数量；
(4) filesUploaded：表示已经上传的文件数量；
随后，当html5.jsp页面完全加载后，便触发window.onload事件：
window.onload = function() { document.getElementById('files').addEventListener( 'change', onFileSelect, false); document.getElementById('uploadButton'). addEventListener('click', startUpload, false); }
这段代码将id为files的input元素的change事件映射到onFileSelect()函数，将按钮的click事件映射到startUpload()函数。
每当用户从本地目录中修改了不同的文件时，都会触发change事件。与该事件相关的事件处理器onFileSelect()函数只是在一个id为selectedFiles的output元素中输出已选中的文件的名称和数量：
//trigger when selecting file change function onFileSelect(e) { var files = e.target.files; // FileList object var output = []; //get upload file count fileCount = files.length; totalFileLength = 0; for (var i=0; i<fileCount; i++) { var file = files[i]; output.push(file.name, ' (', file.size, ' bytes, ', file.lastModifiedDate.toLocaleDateString(), ') ' ); output.push('<br/>'); debug('add ' + file.name + ' ('+ file.size + 'bytes' + ') ' ); totalFileLength += file.size; } //show selecting file information document.getElementById('selectedFiles').innerHTML = output.join(''); debug('totalFileLength: ' + totalFileLength + 'bytes'); }
当用户点击Upload按钮时，就会调用startUpload()函数：
//trigger when click Upload button function startUpload() { totalUploaded = filesUploaded = 0; uploadNext(); }
并随着调用uploadNext()函数，uploadNext()函数上传已选文件列表中的下一个文件。它首先创建一个XMLHttpRequest对象和一个FormData对象（表单对象），并将接下来通过document.getElementById('files')获取一个FileList对象，并将要上传的文件添加到属性multipartFile上：
var xhr = new XMLHttpRequest(); var fd = new FormData(); var file = document.getElementById('files'). files[filesUploaded]; fd.append("multipartFile", file);
随后，uploadNext()函数将XMLHttpRequest对象的progress事件绑定添加到onUploadProgress()，并将load事件和error时间分别添加到onUploadComplete()和onUploadFalied：
xhr.upload.addEventListener( "progress", onUploadProgress, false); xhr.addEventListener("load", onUploadComplete, false); xhr.addEventListener("error", onUploadFailed, false);
接下来，打开一个服务器连接,请求/upload-file页面，并发出FormData：
xhr.open("POST", "upload-file");
debug('uploading ' + file.name);
xhr.send(fd);
fd是一个表单对象，该对象的各个属性会被绑定到/upload-file页面对应的请求处理方法saveFile()的模型参数uploadedFile的各个属性上：
public void saveFile(HttpServletRequest servletRequest, @ModelAttribute UploadedFile uploadedFile, BindingResult bindingResult, Model model)
在上传期间，会重复的调用onUploadProgress()函数，让它有机会更新进度条。更新包括计算已经上传的总字节比率，计算已选择文件的字节数，拓宽progressBar div元素里面的div元素：
//progress event of XMLHttpRequest object function onUploadProgress(e) { if (e.lengthComputable) { var percentComplete = parseInt( (e.loaded + totalUploaded) * 100 / totalFileLength); var bar = document.getElementById('bar'); bar.style.width = percentComplete + '%'; bar.innerHTML = percentComplete + ' % complete'; } else { debug('unable to compute'); } }
上传完成时，调用onUploadComplete()函数。这个事件处理器会添加totalUploaded，即已经完成上传的文件容量，并添加filesUploaded值。随后，它会查看已经选中的所有文件是否都已经上传，如果是，则会显示一条消息，告诉用户文件上传已经成功完成，如果不是，则再次调用uploadNext()：
//load event of XMLHttpRequest object function onUploadComplete(e) { totalUploaded += document.getElementById('files'). files[filesUploaded].size; filesUploaded++; debug('complete ' + filesUploaded + " of " + fileCount); debug('totalUploaded: ' + totalUploaded); if (filesUploaded < fileCount) { uploadNext(); } else { var bar = document.getElementById('bar'); bar.style.width = '100%'; bar.innerHTML = '100% complete'; alert('Finished uploading file(s)'); } }
如果上传失败，则会调用onUploadFailed()函数，并且显示一条消息：
//error event of XMLHttpRequest object function onUploadFailed(e) { alert("Error uploading file"); }
4、测试
在浏览器中中输入如下URL：
http://localhost:8008/upload2/html5
选中几个文件，并单击Upload按钮，将会看到一个进度条、以及文件上传的信息，如下：
注意：如果有中文，则有必要将整个应用的字符编码设置为UTF-8。
参考文章
[2]Spring MVC学习指南
[3]FormData对象
