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@MultipartConfig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”。