Spring MVC 實戰：表單資料驗證與檔案上傳完整指南

Spring MVC 實戰：表單資料驗證與檔案上傳

本文承接 Spring 學習筆記系列，詳細說明如何在 Spring MVC 中使用 JSR-303 Bean Validation 進行表單驗證，以及配置 Multipart 支援實現檔案上傳。

一、表單資料驗證

1. 依賴引入

<dependency>
  <groupId>javax.validation</groupId>
  <artifactId>validation-api</artifactId>
  <version>1.1.0.Final</version>
</dependency>
<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-validator</artifactId>
  <version>5.2.4.Final</version>
</dependency>

注意：javax.validation 僅定義 API，必須搭配實作（如 Hibernate Validator）否則會報錯。

2. 常用驗證註解

3. 實體類別加上註解

public class User implements Serializable {
    @Size(min = 1, max = 32, message = "帳號長度應在 1-32 位之間")
    private String username;

    @NotEmpty(message = "密碼不能為空")
    private String password;

    @NotEmpty(message = "Email 不能為空")
    @Email(message = "Email 格式不正確")
    private String email;

    @Size(min = 11, max = 11, message = "手機號長度必須為 11 位")
    private String cellphone;
    // getter/setter 省略
}

4. Controller 套用 @Valid

@Controller
@RequestMapping("/user")
public class UserController {
    private final UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @RequestMapping(value = "/register", method = RequestMethod.POST)
    public String processRegistration(@Valid User user, Errors errors) {
        if (errors.hasErrors()) {
            return "register"; // 驗證失敗返回註冊頁
        }
        // 業務邏輯...
        return "redirect:/user/" + user.getUsername();
    }
}

5. JSP 頁面顯示錯誤

<%@ taglib prefix="sf" uri="https://www.springframework.org/tags/form" %>
<sf:form method="POST" action="/register/user/register" commandName="user">
  <sf:errors path="*" element="div" cssClass="errors"/><br/>
  <table>
    <tr><td>UserName:</td><td><sf:input path="username" cssErrorClass="errors"/></td></tr>
    <tr><td>Password:</td><td><sf:password path="password" cssErrorClass="errors"/></td></tr>
    <tr><td>Email:</td><td><sf:input path="email" cssErrorClass="errors"/></td></tr>
    <tr><td>CellPhone:</td><td><sf:input path="cellphone" cssErrorClass="errors"/></td></tr>
  </table>
  <input type="submit" value="Register"/>
</sf:form>

二、檔案上傳

Spring 檔案上傳僅需三步：

1. 配置 Multipart 參數（繼承 AbstractAnnotationConfigDispatcherServletInitializer）

@Override
protected void customizeRegistration(ServletRegistration.Dynamic registration) {
    registration.setMultipartConfig(new MultipartConfigElement(
        "/tmp/uploads",  // 臨時檔案目錄
        2097152,         // 單檔最大 2MB
        4194304,         // 請求總大小最大 4MB
        0                // 檔案大小閾值，0 表示直接寫磁碟
    ));
}

2. 註冊 MultipartResolver Bean

@Bean
public MultipartResolver multipartResolver() throws IOException {
    return new StandardServletMultipartResolver();
}

3. Controller 處理上傳

@RequestMapping(value = "/{username}", method = RequestMethod.POST)
public String showUserInfo(@RequestPart("icon") MultipartFile icon) throws IOException {
    icon.transferTo(new File("/upload/path/" + icon.getOriginalFilename()));
    return "user";
}

4. 前端表單

<form method="post" enctype="multipart/form-data">
  <label>上傳頭像圖片?</label>
  <input type="file" name="icon" accept="image/jpeg, image/png" />
  <button type="submit">確定</button>
</form>

關鍵點：表單必須設定 enctype="multipart/form-data"；推薦使用 MultipartFile 介面而非 byte[]，可取得檔案名、大小、類型等資訊。