如何从对象的列表类型的属性中提取 json 的数组

Question

我正在使用 Flickr API 获取图像信息和 returns 以下 JSON:

{"photos":{"page":1,"pages":60,"perpage":100,"total":"5964","photo":[{"id":"21577339501","owner":"85277110@N02","secret":"31e850dfeb","server":"5785","farm":6,"title":"P1390956","ispublic":1,"isfriend":0,"isfamily":0}, {"id":"21577287101","owner":"85277110@N02","secret":"412990658f","server":"611","farm":1,"title":"P1400012","ispublic":1,"isfriend":0,"isfamily":0}]

我在 Spring 控制器中使用此代码反序列化 JSON:

Collection<Photos> readValues = objectMapper.readValue(new URL(url), new TypeReference<Collection<Photos>>() { });

而returns出现如下错误：

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

我该如何解决这个问题？我没有找到解决方案。

Photos.class:

public class Photos {

    @JsonProperty("page")
    private Integer page;

    @JsonProperty("pages")
    private Integer pages;

    @JsonProperty("perpage")
    private Integer perpage;

    @JsonProperty("total")
    private Integer total;

    @JsonProperty("photo")
    @JsonDeserialize(contentAs = Photo.class, as = ArrayList.class)
    private List<Photo> photo;

    public Photos() {}

    public Photos(Integer page, Integer pages, Integer perpage, Integer total,
            List<Photo> photo) {
        super();
        this.page = page;
        this.pages = pages;
        this.perpage = perpage;
        this.total = total;
        this.photo = photo;
    }

    public Photos(List<Photo> photo) {
        super();
        this.photo = photo;
    }

    public Integer getPage() {
        return page;
    }
    public void setPage(Integer page) {
        this.page = page;
    }
    public Integer getPages() {
        return pages;
    }
    public void setPages(Integer pages) {
        this.pages = pages;
    }
    public Integer getPerpage() {
        return perpage;
    }
    public void setPerpage(Integer perpage) {
        this.perpage = perpage;
    }
    public Integer getTotal() {
        return total;
    }
    public void setTotal(Integer total) {
        this.total = total;
    }
    public List<Photo> getPhoto() {
        return photo;
    }

    public void setPhoto(List<Photo> photo) {
        this.photo = photo;
    }
}

Photo.class:

public class Photo {

    @JsonProperty("id")
    private Integer id;

    @JsonProperty("owner")
    private String owner;

    @JsonProperty("secret")
    private String secret;

    @JsonProperty("server")
    private Integer server;

    @JsonProperty("farm")
    private Integer farm;

    @JsonProperty("title")
    private String title;

    @JsonProperty("ispublic")
    private Boolean isPublic;

    @JsonProperty("isfriend")
    private Boolean isFriend;

    @JsonProperty("isfamily")
    private Boolean isFamily;

    public Photo() { }

    public Photo(Integer id, String owner, String secret, Integer server,
            Integer farm, String title, Boolean isPublic, Boolean isFriend,
            Boolean isFamily) {
        super();
        this.id = id;
        this.owner = owner;
        this.secret = secret;
        this.server = server;
        this.farm = farm;
        this.title = title;
        this.isPublic = isPublic;
        this.isFriend = isFriend;
        this.isFamily = isFamily;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getOwner() {
        return owner;
    }
    public void setOwner(String owner) {
        this.owner = owner;
    }
    public String getSecret() {
        return secret;
    }
    public void setSecret(String secret) {
        this.secret = secret;
    }
    public Integer getServer() {
        return server;
    }
    public void setServer(Integer server) {
        this.server = server;
    }
    public Integer getFarm() {
        return farm;
    }
    public void setFarm(Integer farm) {
        this.farm = farm;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public Boolean getIsPublic() {
        return isPublic;
    }
    public void setIsPublic(Boolean isPublic) {
        this.isPublic = isPublic;
    }
    public Boolean getIsFriend() {
        return isFriend;
    }
    public void setIsFriend(Boolean isFriend) {
        this.isFriend = isFriend;
    }
    public Boolean getIsFamily() {
        return isFamily;
    }
    public void setIsFamily(Boolean isFamily) {
        this.isFamily = isFamily;
    }

}

Answer 1

基本问题是你的 json 是不是一个 Collection<Photos>，而是一个 Map<String, Photos>，它只有一个条目 "photos" -> Photos instance.

通过进行以下更改，我让您的 json 成功反序列化...

A) 更改正在读取的类型：

Map<String, Photos> readValues = objectMapper.readValue(json, new TypeReference<Map<String, Photos>>() { });

请注意，我是直接从字符串（而不是 URL）读取的。

B) 将 Photo.id 的类型从 Integer 更改为 Long，因为您的 json 的 id 值远远超过最大 int 大小。

C) 我添加了您的示例 json 中缺失的两个右大括号以使其有效。

仅供参考，反序列化在 Photos 的 List<Photo> photo 字段上使用或不使用 @JsonDeserialize 注释都有效。

这里有一些可以运行的代码：

String json = "{\"photos\":{\"page\":1,\"pages\":60,\"perpage\":100,\"total\":\"5964\",\"photo\":[{\"id\":\"21577339501\",\"owner\":\"85277110@N02\",\"secret\":\"31e850dfeb\",\"server\":\"5785\",\"farm\":6,\"title\":\"P1390956\",\"ispublic\":1,\"isfriend\":0,\"isfamily\":0}, {\"id\":\"21577287101\",\"owner\":\"85277110@N02\",\"secret\":\"412990658f\",\"server\":\"611\",\"farm\":1,\"title\":\"P1400012\",\"ispublic\":1,\"isfriend\":0,\"isfamily\":0}]}}"; 
Map<String, Photos> readValues = new ObjectMapper().readValue(json, new TypeReference<Map<String, Photos>>() { });

如何从对象的列表类型的属性中提取 json 的数组

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