chapter07_SpringMVC的高级技术_2_处理Multipart形式的数据

multipart格式的数据会将一个form拆分成多个part，每个part对应一个输入域

(1) Spring中解析Multipart交给了MultipartResolver接口的实现类

(2) Spring内置了 MultipartResolver的实现类， CommonsMultipartResolver 和 StandardServletMultipartResolver，更优的选择是StandardServletMultipartResolver

CommonsMultipartResolver的配置 P209
StandardServletMultipartResolver的配置

(1) 首先声明为bean

(2) 然后

1 实现 WebApplicationInitializer接口的customizeRegistration()方法中调用setMultipartConfig方法

或

2 在 AnnotationConfigDispatcherServletInitializer(DispatcherServlet)重载customizeRegistration()方法

示例
```
  public class SpitterWebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

      ...

      @Override
      protected void customizeRegistration(Dynamic registration) {

          registration.setMultipartConfig(new MultipartConfigElement("/", 2097152, 4194304, 0));
      }
  }
```
其中，MultipartConfigElement的构造函数public MultipartConfigElement(String location, long maxFileSize, long maxRequestSize, int fileSizeThreshold)的几个参数分别代表:上传路径, 文件的最大容量(byte), 整个multipart请求的最大容量(byte), 写入到磁盘上的最小文件大小

表单form中的multipart

(1) 示例

  <html xmlns:th="http://www.thymeleaf.org">

  ...

  <body>

  ...

      <div id="content">
          <h1>Register</h1>

          <form method="POST" th:object="${spitter}" enctype="multipart/form-data">
              <div class="errors" th:if="${#fields.hasErrors('*')}">
                  <ul>
                      <li th:each="err : ${#fields.errors('*')}" th:text="${err}">Input is incorrect
                      </li>
                  </ul>
              </div>
  
              <label th:class="${#fields.hasErrors('firstName')}? 'error'">First Name</label>:
              <input type="text" th:field="*{firstName}" th:class="${#fields.hasErrors('firstName')}? 'error'"/>
              <br/>

              <label th:class="${#fields.hasErrors('lastName')}? 'error'">Last Name</label>:
              <input type="text" th:field="*{lastName}" th:class="${#fields.hasErrors('lastName')}? 'error'"/>
              <br/>

              <label th:class="${#fields.hasErrors('email')}? 'error'">Email</label>:
              <input type="text" th:field="*{email}" th:class="${#fields.hasErrors('email')}? 'error'"/>
              <br/>

              <label th:class="${#fields.hasErrors('username')}? 'error'">Username</label>:
              <input type="text" th:field="*{username}" th:class="${#fields.hasErrors('username')}? 'error'"/>
              <br/>

              <label th:class="${#fields.hasErrors('password')}? 'error'">Password</label>:
              <input type="password" th:field="*{password}" th:class="${#fields.hasErrors('password')}? 'error'"/>
              <br/>

              <label>Profile Picture</label>:
              <input type="file" name="profilePicture" accept="image/jpeg,image/png,image/gif"/>
              <br/>

              <input type="submit" value="Register"/>
          </form>
      </div>

      ...
  </body>
  </html>

(2)

form中的enctype属性设置为multipart/form-data,告诉浏览器以multipart形式提交表单，而不是以表单数据的形式提交。这样的结果是每个 <.input> 元素会对应一个part

(3)

这个input的元素type为file，可以让用户选择要上传的文件；accept属性限定了上传文件的类型；name和Controller中要处理的参数名对应

Controller中处理multipart数据

(1) 示例 FileUploadController.java

  @Controller
  @RequestMapping("/fileupload")
  public class FileUploadController {

      @RequestMapping(method = RequestMethod.GET)
      public String uploadForm() {

          return "uploadForm";
      }

      @RequestMapping(method = RequestMethod.POST)
      public String processUpload(
          @RequestPart("file") MultipartFile file) {

          return "redirect:/";
      }
  }

(2) 添加 @RequestPart注解

@RequestPart(“file”) MultipartFile file 代表从form中读取name为file的文件

(3) MultipartFile接口有很多好用的方法 P212

例如 transferTo()方法可以把文件保存到本地

(4) 替代MultipartFile的方案是使用Part，具体操作和MultipartFile类似，只不过不需要配置MultipartResolver

示例 SpitterController.java

  @Controller
  @RequestMapping("/spitter")
  public class SpitterController {

      ...

      @RequestMapping(value = "/register", method = POST)
      public String processRegistration(
          @RequestPart(value = "profilePicture") MultipartFile profilePicture,
          @Valid Spitter spitter,
          Errors errors) throws IllegalStateException, IOException {

          if (errors.hasErrors()) {
              return "registerForm";
          }

          spitterRepository.save(spitter);

          profilePicture.transferTo(new File("/" + spitter.getUsername() + ".png"));

          return "redirect:/spitter/" + spitter.getUsername();
      }
  }

chapter07_SpringMVC的高级技术_2_处理Multipart形式的数据

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