Spring MVC中处理表单数据：GET与POST请求的分离策略

// ListingForm.java
public class ListingForm {
    private Integer id;
    private Integer userId;
    private String title;

    // 构造函数
    public ListingForm() {}

    public ListingForm(Integer id, Integer userId, String title) {
        this.id = id;
        this.userId = userId;
        this.title = title;
    }

    // Getters and Setters
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }
    public Integer getUserId() { return userId; }
    public void setUserId(Integer userId) { this.userId = userId; }
    public String getTitle() { return title; }
    public void setTitle(String title) { this.title = title; }

    @Override
    public String toString() {
        return "ListingForm{" +
               "id=" + id +
               ", userId=" + userId +
               ", title='" + title + '\'' +
               '}';
    }
}

// ListingDto.java
public class ListingDto {
    private Integer id;
    private Integer userId;
    private String title;

    public ListingDto(Integer id, Integer userId, String title) {
        this.id = id;
        this.userId = userId;
        this.title = title;
    }

    // Getters
    public Integer getId() { return id; }
    public Integer getUserId() { return userId; }
    public String getTitle() { return title; }
}

// ListingService.java (简化版)
import org.springframework.stereotype.Service;
import java.util.HashMap;
import java.util.Map;

@Service
public class ListingService {
    private final Map<Integer, ListingDto> listings = new HashMap<>();
    private Integer nextId = 1;

    public ListingService() {
        // 预填充一些数据
        addListing(new ListingDto(null, 101, "Initial Listing A"));
        addListing(new ListingDto(null, 102, "Initial Listing B"));
    }

    public ListingDto getListingById(Integer id) {
        return listings.get(id);
    }

    public ListingDto addListing(ListingDto listingDto) {
        if (listingDto.getId() == null) {
            listingDto = new ListingDto(nextId++, listingDto.getUserId(), listingDto.getTitle());
        }
        listings.put(listingDto.getId(), listingDto);
        return listingDto;
    }

    public ListingDto updateListing(ListingDto listingDto) {
        if (listings.containsKey(listingDto.getId())) {
            listings.put(listingDto.getId(), listingDto);
            return listingDto;
        }
        return null; // 或者抛出异常
    }

    public void deleteListingById(Integer id) {
        listings.remove(id);
    }
}

import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Controller; // 使用 @Controller 适用于返回视图
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.server.ResponseStatusException;

@Controller // 如果是返回HTML视图，使用 @Controller
@RequestMapping("/listings") // 统一前缀
public class ListingController {

    private final ListingService listingService;

    public ListingController(ListingService listingService) {
        this.listingService = listingService;
    }

    // 1. GET请求：用于显示编辑表单并预填充数据
    @GetMapping("/edit/{id}")
    public String showEditListingForm(@PathVariable Integer id, Model model) {
        ListingDto existingListing = listingService.getListingById(id);
        if (existingListing == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Listing with ID " + id + " not found.");
        }

        // 将现有数据转换为表单对象，并添加到Model中，供视图渲染
        ListingForm listingForm = new ListingForm(existingListing.getId(), existingListing.getUserId(), existingListing.getTitle());
        model.addAttribute("listingForm", listingForm);
        model.addAttribute("submitURL", String.format("/listings/edit/%s", id)); // 提供提交URL给视图

        return "editListing"; // 返回视图名称 (例如: editListing.html 或 editListing.jsp)
    }

    // 2. POST请求：用于接收和处理表单提交的数据
    @PostMapping("/edit/{id}")
    public String submitEditedListing(@PathVariable Integer id,
                                      @ModelAttribute ListingForm submittedListingForm, // 绑定表单数据
                                      Model model) {

        // 验证路径ID与表单ID的一致性（可选但推荐）
        if (submittedListingForm.getId() != null && !submittedListingForm.getId().equals(id)) {
            // 如果ID不匹配，可以抛出异常或重定向到错误页面
            throw new IllegalArgumentException("Listing ID in path does not match ID in form data.");
        }

        // 将表单数据转换为DTO，用于服务层处理
        ListingDto updatedListingDto = new ListingDto(id, submittedListingForm.getUserId(), submittedListingForm.getTitle());

        // 调用服务层更新数据
        ListingDto result = listingService.updateListing(updatedListingDto);

        if (result == null) {
            // 处理更新失败的情况
            model.addAttribute("error", "Failed to update listing.");
            return "editListing"; // 返回到编辑页面并显示错误
        }

        // 重定向到列表页或详情页，遵循PRG模式 (Post/Redirect/Get)
        return "redirect:/listings/" + id; // 假设有一个详情页
    }

    // 假设的列表详情页
    @GetMapping("/{id}")
    public String viewListingDetails(@PathVariable Integer id, Model model) {
        ListingDto listing = listingService.getListingById(id);
        if (listing == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Listing with ID " + id + " not found.");
        }
        model.addAttribute("listing", listing);
        return "listingDetails"; // 视图名称
    }
}

<!-- src/main/resources/templates/editListing.html -->
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Edit Listing</title>
</head>
<body>
    <h1>Edit Listing</h1>
    <form th:action="${submitURL}" th:object="${listingForm}" method="post">
        <!-- 注意：如果ID不希望用户修改，可以使用隐藏字段 -->
        <input type="hidden" th:field="*{id}" />

        <label for="userId">User ID:</label>
        <input type="text" id="userId" th:field="*{userId}" /><br/>

        <label for="title">Title:</label>
        <input type="text" id="title" th:field="*{title}" /><br/>

        <button type="submit">Save Changes</button>
    </form>

    <div th:if="${error}" style="color: red;">
        <p th:text="${error}"></p>
    </div>
</body>
</html>

<!-- src/main/resources/templates/listingDetails.html -->
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Listing Details</title>
</head>
<body>
    <h1>Listing Details</h1>
    <p>ID: <span th:text="${listing.id}"></span></p>
    <p>User ID: <span th:text="${listing.userId}"></span></p>
    <p>Title: <span th:text="${listing.title}"></span></p>
    <a th:href="@{/listings/edit/{id}(id=${listing.id})}">Edit Listing</a>
</body>
</html>