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”。