java - 使用 Jackson 映射 JSON 时遇到问题

Question

我需要映射以下 JSON:

[{"id":7346,"name":"The Legend of Zelda: Breath of the Wild","cover":{"url":"//images.igdb.com/igdb/image/upload/t_thumb/jk9el4ksl4c7qwaex2y5.jpg","cloudinary_id":"jk9el4ksl4c7qwaex2y5","width":2709,"height":3816}},{"id":2909,"name":"The Legend of Zelda: A Link Between Worlds","cover":{"url":"//images.igdb.com/igdb/image/upload/t_thumb/r9ezsk5yhljc83dfjeqc.jpg","cloudinary_id":"r9ezsk5yhljc83dfjeqc","width":406,"height":362}}]

它看起来像这样: JSON

当我不需要“cover”字段时(我的域类只有 ID 和名称)，映射它没有任何问题。现在，当我需要它时我也遇到了问题。

这是我用来将 JSON 映射为字符串的代码行(就像我说的，如果我只坚持 id 和 name 字段，它就可以正常工作)。

List<Suggestion> suggestions = mapper.readValue(requestString, new TypeReference<List<Suggestion>>(){});

我的Suggestion.java类(class):

public class Suggestion {

private long id;
private String name;
private Cover cover;

public Suggestion(){
}

public Suggestion(long id, String name, Cover cover) {
    this.id = id;
    this.name = name;
    this.cover = cover;
}

public long getId() {
    return id;
}

public String getName() {
    return name;
}

public Cover getCover() {
    return cover;
}

}

我的Cover.java类:

public class Cover {
    private String url;
    private String cloudinaryId;
    private Integer width;
    private Integer height;

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getCloudinaryId() {
        return cloudinaryId;
    }

    public void setCloudinaryId(String cloudinaryId) {
        this.cloudinaryId = cloudinaryId;
    }

    public Integer getWidth() {
        return width;
    }

    public void setWidth(Integer width) {
        this.width = width;
    }

    public Integer getHeight() {
        return height;
    }

    public void setHeight(Integer height) {
        this.height = height;
    }

}

我用过http://www.jsonschema2pojo.org/得到这个想法(附加属性肯定不是必需的)，我不确定为什么它不再起作用。

那么这里可能存在什么问题呢？

Answer 1

让我们检查一下导致问题的原因。如果您使用您提供的类运行代码，您将收到以下异常:

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "cloudinary_id"

示例中的 JSON 如下:

[
  {
    "id": 7346,
    "name": "The Legend of Zelda: Breath of the Wild",
    "cover": {
      "url": "//images.igdb.com/igdb/image/upload/t_thumb/jk9el4ksl4c7qwaex2y5.jpg",
      "cloudinary_id": "jk9el4ksl4c7qwaex2y5",
      "width": 2709,
      "height": 3816
    }
  },
  {
    "id": 2909,
    "name": "The Legend of Zelda: A Link Between Worlds",
    "cover": {
      "url": "//images.igdb.com/igdb/image/upload/t_thumb/r9ezsk5yhljc83dfjeqc.jpg",
      "cloudinary_id": "r9ezsk5yhljc83dfjeqc",
      "width": 406,
      "height": 362
    }
  }
]

您错过的是使用 @JsonProperty 注释指定 JSON 到属性字段映射。将您的 Cover 类更新为:

public class Cover {

    private String url;
    @JsonProperty("cloudinary_id")
    private String cloudinaryId;
    private Integer width;
    private Integer height;

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getCloudinaryId() {
        return cloudinaryId;
    }

    public void setCloudinaryId(String cloudinaryId) {
        this.cloudinaryId = cloudinaryId;
    }

    public Integer getWidth() {
        return width;
    }

    public void setWidth(Integer width) {
        this.width = width;
    }

    public Integer getHeight() {
        return height;
    }

    public void setHeight(Integer height) {
        this.height = height;
    }
}

当 JSON 字段 1:1 映射到类字段名称时，您不必使用此注释。当 JSON 使用与 Java 类不同的命名时，这是必需的。