Spring MVC 使用介绍(十四)文件上传下载

一、概述

文件上传时,http请求头Content-Type须为multipart/form-data,有两种实现方式:

1、基于FormData对象,该方式简单灵活

2、基于<form>表单元素,method设为POST,enctype设置为multipart/form-data,在form表单上提交

web容器收到该请求时,须根据请求头将字节流解析为文件对象,spring mvc 提供了MultipartResolver、MultipartFile两个接口用于支持文件上传功能

二、MultipartResolver & MultipartFile

1、MultipartResolver接口提供了文件解析功能,其定义如下:

public interface MultipartResolver {
boolean isMultipart(HttpServletRequest request);
MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException;
void cleanupMultipart(MultipartHttpServletRequest request);
}

Spring MVC使用Apache Commons fileupload技术实现了一个MultipartResolver实现类:CommonsMultipartResolver

2、MultipartFile接口代表上传的文件,提供了文件操作的相关功能,其定义如下:

public interface MultipartFile {
String getName();
String getOriginalFilename(); // 原文件名
String getContentType();
boolean isEmpty();
long getSize();
byte[] getBytes() throws IOException;
InputStream getInputStream() throws IOException; // 获取文件流
void transferTo(File dest) throws IOException, IllegalStateException; // 保存文件
}

三、使用示例

1、添加pom依赖

<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.4</version>
</dependency>

2、spring-mvc.xml中配置MultipartResolver

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<!-- 上传文件大小限制,单位为字节-10Mb -->
<property name="maxUploadSize">
<value>10485760</value>
</property>
<!-- 请求的编码格式 -->
<property name="defaultEncoding">
<value>UTF-8</value>
</property>
</bean>

3、controller

@Controller
public class FileController {
/**
* 文件存储目录
*/
private static final String uploadFolder = "d:/upload-file/"; /**
* 上传
*/
@ResponseBody
@RequestMapping(value = "/upload", method = RequestMethod.POST)
public Map<String, String> fileUpload(@RequestParam("file") MultipartFile file, @RequestParam("fileType") String fileType) throws Exception { // 创建文件目录
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM");
String dateStr = sdf.format(new Date());
String dirPath = uploadFolder + dateStr;
File dir = new File(dirPath);
if (!dir.exists()) {
dir.mkdirs();
} // 保存文件
String fileName = UUID.randomUUID() + this.getFileNameSuffix(file.getOriginalFilename());
File savedFile = new File(dir + "/" + fileName);
file.transferTo(savedFile); Map<String, String> result = new HashMap<String, String>();
result.put("fileName", file.getOriginalFilename());
result.put("fileType", fileType);
result.put("filePath", dateStr + "/" + fileName); return result;
} /**
* 下载
*/
@RequestMapping("/download")
public void downloadFile(@RequestParam(value = "fileName", required = false) String fileName, @RequestParam("filePath") String filePath, HttpServletResponse response) throws Exception {
File file = new File(uploadFolder + filePath);
if (!file.exists()) {
return;
} // 读取字节流到缓存
InputStream in = new BufferedInputStream(new FileInputStream(file));
byte[] buffer = new byte[in.available()];
in.read(buffer);
in.close(); // 设置ContentType
String suff = this.getFileNameSuffix(file.getName());
if (suff != null) {
suff = suff.toLowerCase();
}
switch (suff) {
case ".jpg":
case ".jpeg":
response.setContentType(MediaType.IMAGE_JPEG_VALUE);
break;
case ".png":
response.setContentType(MediaType.IMAGE_PNG_VALUE);
break;
case ".gif":
response.setContentType(MediaType.IMAGE_GIF_VALUE);
break;
default:
response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
break;
} // 输出
response.addHeader("Content-Disposition", "attachment;filename=\"" + (StringUtils.isEmpty(fileName) ? file.getName() : fileName));
response.addHeader("Content-Length", "" + file.length());
response.setContentType("application/x-msdownload");
OutputStream out = new BufferedOutputStream(response.getOutputStream());
out.write(buffer);
out.flush();
} /**
* 获取文件名后缀*/
private String getFileNameSuffix(String fileName) { if (StringUtils.isEmpty(fileName)) {
return null;
} String suffix;
int index = fileName.lastIndexOf(".");
if (index == -1) {
suffix = null;
}
else {
suffix = fileName.substring(index);
} return suffix;
}
}

4、前端页面(test.html)

<!DOCTYPE html>
<html>
<head>
<title>test page</title>
</head>
<body>
<div>
<input id="upload" type="file" onchange="uploadFile(event)" />
</div>
<div>
<input id="download" type="button" onclick="downloadFile()" value="下载" />
</div>
</body>
<script>
var context = '/test' function uploadFile(event) {
// 文件类型过滤
var file = event.currentTarget.files[0];
var fileName = file.name;
if (/\.(jpg|jpeg|png|gif)$/i.test(fileName) == false) {
alert('提示', '不支持的图片类型,头像只支持.jpg,.jpeg,.png,.gif');
return;
} var formData = new FormData();
formData.append('fileType', 'portrait');
formData.append('file', event.currentTarget.files[0]); // 发送请求
var xhr = new XMLHttpRequest();
xhr.open('POST', context + '/upload', true);
xhr.onreadystatechange = function() {
if (xhr.readyState==4 && xhr.status==200) {
document.getElementById('download').fileData = JSON.parse(xhr.responseText);
alert("上传成功");
}
}
xhr.send(formData); // 重置文件上传控件,使得重复选择同一个文件时,onchange依旧触发
event.target.value = null;
} function downloadFile() {
var fileData = document.getElementById('download').fileData;
location.href = context + '/download?filePath=' + decodeURIComponent(fileData.filePath) + '&fileName=' + decodeURIComponent(fileData.fileName);
}
</script>
</html>

访问http://file-test/test.html,可测试文件的上传下载功能

补充:示例使用@ResponseBody输出json数据,因此还需添加相关配置,详细可参考Spring MVC 使用介绍(五)—— 注解式控制器(一):基本介绍

另外,文件下载除了示例中文件流方式,还可以基于spring对静态文件的支持功能,详细可参考Spring MVC 使用介绍(十一)—— 跨域与静态资源访问

参考:

Spring MVC的文件上传

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