虽然Servlet3.0+中上传文件，我们在服务端编程即可非常容易，但是用户体验却不是非常友好。单独的一个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。
不管是Java小程序，Flash 或者Silverlight都有其局限性，好在html5可以很方便的解决这些问题。
首先HTML5在其DOM中添加了一个File API，它允许访问本地文件。
示例
工程结构：
UploadedFile.java
package com.artisan.domain; import java.io.Serializable; import org.springframework.web.multipart.MultipartFile; public class UploadedFile implements Serializable { private static final long serialVersionUID = 72348L; private MultipartFile multipartFile; public MultipartFile getMultipartFile() { return multipartFile; } public void setMultipartFile(MultipartFile multipartFile) { this.multipartFile = multipartFile; } }
Html5FileUploadController.java
package com.artisan.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 com.artisan.domain.UploadedFile; @Controller public class Html5FileUploadController { private static final Log logger = LogFactory .getLog(Html5FileUploadController.class); @RequestMapping(value = "/html5") public String inputProduct() { return "Html5"; } @RequestMapping(value = "/file_upload") public void saveFile(@ModelAttribute UploadedFile uploadedFile, BindingResult bindingResult, Model model) { MultipartFile multipartFile = uploadedFile.getMultipartFile(); logger.info("fileName:" + multipartFile.getOriginalFilename()); String fileName = multipartFile.getOriginalFilename(); try { File file = new File("D:/", fileName); multipartFile.transferTo(file); logger.info("save files successfully"); } catch (IOException e) { e.printStackTrace(); } } }
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"> <!-- 扫描控制层的注解，使其成为Spring管理的Bean --> <context:component-scan base-package="com.artisan.controller" /> <!-- 静态资源文件 --> <mvc:annotation-driven /> <mvc:resources mapping="/css/**" location="/css/" /> <mvc:resources mapping="/*.jsp" location="/" /> <!-- 视图解析器 --> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/" /> <property name="suffix" value=".jsp" /> </bean> <!-- SpringMVC上传文件时，需要配置MultipartResolver处理器 --> <bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"> </bean> </beans>
web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.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>-1</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> <!-- 避免中文乱码 --> <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> <init-param> <param-name>forceEncoding</param-name> <param-value>true</param-value> </init-param> </filter> <filter-mapping> <filter-name>characterEncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app>
前台页面：
我们关注的是HTML5 input元素的change事件，当input元素的值发生改变时，就会被触发。其次，我们还关注XMLHttpRequest对象中添加progress事件。XMLHttpRequest自然是AJAX的骨架。当异步使用XMLHttpRequest对象上传文件的时候就会持续地触发progress事件，直到上传进度完成或者取消。通过轻松监听progress事件，可以轻松地检测文件上传操作的进度。
<!DOCTYPE HTML> <html> <head> <script> var totalFileLength, totalUploaded, fileCount, filesUploaded; //输出调试信息 function debug(s) { var debug = document.getElementById('debug'); if (debug) { debug.innerHTML = debug.innerHTML + '<br/>' + s; } } //当一个文件上传完成，紧接着开始调用下次upLoadNext(); 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)'); } } //当选择的文件发生改变时，重新获取并打印现在所选的文件信息 function onFileSelect(e) { var files = e.target.files; // FileList object var output = []; 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.size); totalFileLength += file.size; } document.getElementById('selectedFiles').innerHTML = output.join(''); debug('totalFileLength:' + totalFileLength); } //当进度发生改变时，改变进度条 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'); } } function onUploadFailed(e) { alert("Error uploading file"); } //将XMLHttpRequest对象的progress事件添加到onLoadProgress并将load事件和error事件分别绑定到对应方法。 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", "file_upload"); debug('uploading ' + file.name); xhr.send(fd); } //当用户点击提交以后开始执行 function startUpload() { totalUploaded = filesUploaded = 0; uploadNext(); } 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:100px;border:2px solid green;overflow:auto'> </div> </body> </html>
progressBar div用于展示上传进度，debug div用于显示调试信息。
执行脚本时，第一件事就是为4个变量分配空间：totalFileLength,totalUploaded,fileCount,filesUploaded;
- totalFileLength:主要用于保存上传文件的总长度。
- totalUploaded:指示目前已经上传的字节数。
- fileCount：包含了要上传的文件数量。
- fileUploaded：指示了已经上传的文件数量。
测试
初始页面：
选择多个文件：
上传文件：
查看目标目录：
源码
代码已提交到github
https://github.com/yangshangwei/SpringMvcTutorialArtisan
