从YuGiOh! API获取JSON映射为Java Card类的问题求助

核心问题分析 #

1. JSON结构不匹配：API返回的是包含data数组的顶层对象，而非直接的卡牌数组，直接反序列化成card[]会触发类型不匹配错误。
2. 自定义类存在错误：
   • 违反Java命名规范，类名未大写
   • setName方法参数与赋值逻辑错误
   • 缺少Jackson反序列化必需的无参构造函数
   • 图片路径字段未对应API中的card_images[0].image_url节点

修正方案 #

1. 修复自定义Card类 #

package card;

public class Card {
    private int atk;
    private int def;
    private int level;
    private String race;
    private String attribute;
    private String archetype;
    private String imagePath;
    private String name;

    // Jackson反序列化必需的无参构造
    public Card() {}

    // 带参构造（可选）
    public Card(int atk, int def, int level, String name, String attribute, String imagePath) {
        this.atk = atk;
        this.def = def;
        this.level = level;
        this.attribute = attribute;
        this.imagePath = imagePath;
        this.name = name;
    }

    // Getter & Setter
    public int getAtk() { return atk; }
    public void setAtk(int atk) { this.atk = atk; }

    public int getDef() { return def; }
    public void setDef(int def) { this.def = def; }

    public int getLevel() { return level; }
    public void setLevel(int level) { this.level = level; }

    public String getRace() { return race; }
    public void setRace(String race) { this.race = race; }

    public String getAttribute() { return attribute; }
    public void setAttribute(String attribute) { this.attribute = attribute; }

    public String getArchetype() { return archetype; }
    public void setArchetype(String archetype) { this.archetype = archetype; }

    public String getImagePath() { return imagePath; }
    public void setImagePath(String imagePath) { this.imagePath = imagePath; }

    public String getName() { return name; }
    // 修复setName方法错误
    public void setName(String name) { this.name = name; }
}

2. 创建API响应包装类 #

用于匹配API返回的顶层JSON结构：

package card;

import com.fasterxml.jackson.annotation.JsonProperty;
import java.util.List;

public class CardResponse {
    @JsonProperty("data")
    private List<Card> data;

    public List<Card> getData() { return data; }
    public void setData(List<Card> data) { this.data = data; }
}

3. 修正API请求与反序列化逻辑 #

解决流只能读取一次的问题，同时提取图片路径：

import java.net.HttpURLConnection;
import java.net.URL;
import java.util.List;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.JsonNode;

import card.Card;
import card.CardResponse;

public class API {
    
    public void searchCard() {
        try {
            URL url = new URL("https://db.ygoprodeck.com/api/v7/cardinfo.php?name=Dark%");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.connect();

            int responseCode = conn.getResponseCode();
            if (responseCode != 200) {
                throw new RuntimeException("HttpResponseCode: " + responseCode);
            } else {
                // 将流转为字符串，避免重复读取问题
                InputStream inputStream = conn.getInputStream();
                String jsonStr = new String(inputStream.readAllBytes(), StandardCharsets.UTF_8);
                inputStream.close();

                ObjectMapper mapper = new ObjectMapper();
                // 反序列化顶层响应对象
                CardResponse response = mapper.readValue(jsonStr, CardResponse.class);
                List<Card> cardList = response.getData();

                // 提取每个卡牌的图片路径
                JsonNode rootNode = mapper.readTree(jsonStr);
                JsonNode dataNode = rootNode.path("data");

                for (int i = 0; i < cardList.size(); i++) {
                    Card card = cardList.get(i);
                    JsonNode cardDataNode = dataNode.get(i);
                    // 从card_images数组第一个元素获取image_url
                    String imageUrl = cardDataNode.path("card_images").get(0).path("image_url").asText();
                    card.setImagePath(imageUrl);

                    // 测试输出
                    System.out.printf("卡牌：%s，攻击力：%d，图片地址：%s%n", 
                                      card.getName(), card.getAtk(), card.getImagePath());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

关键说明 #

• 必须通过CardResponse接收API返回的顶层对象，再提取内部的data数组
• 确保自定义类符合JavaBean规范（无参构造、正确的Getter/Setter）
• 图片路径需要从API返回的嵌套节点中手动提取，或通过自定义Jackson反序列化器实现自动映射

内容的提问来源于stack exchange，提问作者Lyna DJELMOUDI