使用 Jackson 自定义 JSON 反序列化 [英] Custom JSON Deserialization with Jackson

问题描述

我正在使用 Flickr API.当调用 flickr.test.login 方法，默认 JSON 结果为:

I'm using the Flickr API. When calling the flickr.test.login method, the default JSON result is:

{
    "user": {
        "id": "21207597@N07",
        "username": {
            "_content": "jamalfanaian"
        }
    },
    "stat": "ok"
}

我想将此响应解析为 Java 对象:

I'd like to parse this response into a Java object:

public class FlickrAccount {
    private String id;
    private String username;
    // ... getter & setter ...
}

JSON 属性应该像这样映射:

The JSON properties should be mapped like this:

"user" -> "id" ==> FlickrAccount.id
"user" -> "username" -> "_content" ==> FlickrAccount.username

不幸的是，我无法找到一种使用 Annotations 的漂亮、优雅的方法来执行此操作.到目前为止，我的方法是将 JSON 字符串读入 Map 并从那里获取值.

Unfortunately, I'm not able to find a nice, elegant way to do this using Annotations. My approach so far is, to read the JSON String into a Map<String, Object> and get the values from there.

Map<String, Object> value = new ObjectMapper().readValue(response.getStream(),
        new TypeReference<HashMap<String, Object>>() {
        });
@SuppressWarnings( "unchecked" )
Map<String, Object> user = (Map<String, Object>) value.get("user");
String id = (String) user.get("id");
@SuppressWarnings( "unchecked" )
String username = (String) ((Map<String, Object>) user.get("username")).get("_content");
FlickrAccount account = new FlickrAccount();
account.setId(id);
account.setUsername(username);

但我认为，这是有史以来最不优雅的方式.有没有什么简单的方法，要么使用注解，要么使用自定义反序列化器?

But I think, this is the most non-elegant way, ever. Is there any simple way, either using Annotations or a custom Deserializer?

这对我来说很明显，但当然行不通:

This would be very obvious for me, but of course it doesn't work:

public class FlickrAccount {
    @JsonProperty( "user.id" ) private String id;
    @JsonProperty( "user.username._content" ) private String username;
    // ... getter and setter ...
}

推荐答案

您可以为此类编写自定义反序列化器.它可能看起来像这样:

You can write custom deserializer for this class. It could look like this:

class FlickrAccountJsonDeserializer extends JsonDeserializer<FlickrAccount> {

    @Override
    public FlickrAccount deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        Root root = jp.readValueAs(Root.class);

        FlickrAccount account = new FlickrAccount();
        if (root != null && root.user != null) {
            account.setId(root.user.id);
            if (root.user.username != null) {
                account.setUsername(root.user.username.content);
            }
        }

        return account;
    }

    private static class Root {

        public User user;
        public String stat;
    }

    private static class User {

        public String id;
        public UserName username;
    }

    private static class UserName {

        @JsonProperty("_content")
        public String content;
    }
}

之后，您必须为您的类定义一个反序列化器.您可以按如下方式执行此操作:

After that, you have to define a deserializer for your class. You can do this as follows:

@JsonDeserialize(using = FlickrAccountJsonDeserializer.class)
class FlickrAccount {
    ...
}

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