在Spring MVC框架下利用Servlet3.0 API实现文件上传

Servlet3.0提供了对文件上传的原生支持，不需借助任何第三方组件，直接使用Servlet3.0提供的API就能够实现文件上传功能。本文使用IDEA IDE工具，在Spring MVC框架下，基于注解映射和数据绑定编写Java业务代码，利用Servlet3.0 API来实现单个文件的上传示例。

部署配置文件

MultipartConfig Servlet

在部署描述符中的DispatcherServlet中声明赋值，使其Servlet变成MultipartConfig Servlet，具体添加以下标签内容：

//web.xml
<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/springmvc-servlet.xml</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
<multipart-config>
<max-file-size>1000000</max-file-size>
</multipart-config>
</servlet>
<servlet-mapping>
<servlet-name>springmvc</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>

添加原因：Spring MVC无法直接对Servlet进行注解。另一种方法是用@Multipart
c4e7
Config给DispatcherServlet进行注解，效果一样。

MultipartResolver

在Spring MVC配置文件中添加一个不同的多部分解析器，具体添加以下内容：

//springmvc.servlet.xml
<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver">
</bean>

编写Java代码

Domain类

/**
* UploadFile.java
*
* @author Zero
*/

public class UploadFile implements Serializable {
private static final long serialVersionUID = 123456789L;
private MultipartFile multipartFile;
private String description;

public static long getSerialVersionUID() {
return serialVersionUID;
}
public MultipartFile getMultipartFile() {
return multipartFile;
}
public void setMultipartFile(MultipartFile multipartFile) {
this.multipartFile = multipartFile;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
}

Service接口与实现类

/**
* MyFileService.java
*
* @author Zero
*/

public interface MyFileService {
//MyFileDto loadFileByGuid(String guid);
String uploadFile(UploadFile uploadFile, String realPath);
}

//MyFileServiceImpl.java
@Service("myFileService")
public class MyFileServiceImpl implements MyFileService {
private static final String UPLOAD_ERROR = "文件上传出错!";
private static final String UPLOAD_SUCCESS = "文件上传成功!";

@Override
public String uploadFile(UploadFile uploadFile, String realPath) {
boolean loadFileVerify = false;
MultipartFile multipartFile = uploadFile.getMultipartFile();
String fileName = multipartFile.getOriginalFilename();
File file = new File(realPath, fileName);
try {
multipartFile.transferTo(file);
loadFileVerify = true;
} catch (IOException e) {
e.printStackTrace();
}
return loadFileVerify ? UPLOAD_SUCCESS : UPLOAD_ERROR;
}
}

Controller类

/**
* MyFileController.java
*
* @author Zero
*/

@Controller
@RequestMapping("/public/")
public class MyFileController {

private static Logger LOG = LoggerFactory.getLogger(FileController.class);
private static final String UPLOAD_EMPTY = "文件为空!";

@Autowired
private MyFileService fileService;

@RequestMapping(value = "file_upload", method = RequestMethod.POST)
public String upload(@ModelAttribute(uploadFile) @Valid UploadFile uploadFile, BindingResult result, HttpServletRequest request, Model model) {
if (result.hasErrors()) {
LOG.warn(UPLOAD_EMPTY);
model.addAttribute("uploadResult", UPLOAD_EMPTY);
return "index";
}
String uploadResult = fileService.uploadFile(uploadFile, request.getServletContext().getRealPath("/file"));
model.addAttribute("uploadResult", uploadResult);
return "index";
}
}

编写前端页面代码

编写JSP测试表单

//index.jsp
<form action="public/file_upload" method="post" enctype="multipart/form-data">
<h4>File Upload</h4>
<div class="form-group">
<label for="multipartFile">File select:</label>
<input type="file" name="multipartFile" id="multipartFile"/>
</div>
<div class="form-group">
<label for="description">File description:</label>
<input type="text" name="description" id="description"/>
</div>
<div class="form-group">
<input type="submit" value="upload"/>
<p >${uploadResult}</p>
</div>

</form>

注意事项

1.若BindingResult返回false，可能是domain类参数匹配不对，特别是serialVersionUID，需用idea自生成；

2.若表单post提交的multipartFile数据无法绑定到后台对应属性，可能是表单配置不对enctype=”multipart/form-data”。