Java 使用 Jackson 自定义 JSON 反序列化

Custom JSON Deserialization with Hymanson

提问by Moritz Petersen

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

我正在使用Flickr API。调用该flickr.test.login方法时，默认的 JSON 结果为：

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

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

我想将此响应解析为 Java 对象：

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

The JSON properties should be mapped like this:

JSON 属性应该像这样映射：

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

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.

不幸的是，我无法使用注释找到一种很好的、​​优雅的方法来做到这一点。到目前为止，我的方法是将 JSON 字符串读入 aMap<String, Object>并从那里获取值。

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);

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

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

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

这对我来说很明显，但当然它不起作用：

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

采纳答案by Micha? Ziober

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

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：

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;
    }
}

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

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：

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

回答by tom

You have to make Username a class within FlickrAccount and give it a _content field

您必须在 FlickrAccount 中将 Username 设为一个类，并为其指定一个 _content 字段

回答by Moritz Petersen

Since I don't want to implement a custom class (Username) just to map the username, I went with a little bit more elegant, but still quite ugly approach:

由于我不想实现自定义类 ( Username) 来映射用户名，因此我采用了更优雅但仍然非常丑陋的方法：

ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(in);
JsonNode user = node.get("user");
FlickrAccount account = new FlickrAccount();
account.setId(user.get("id").asText());
account.setUsername(user.get("username").get("_content").asText());

It's still not as elegant as I hoped, but at least I got rid of all the ugly casting. Another advantage of this solution is, that my domain class (FlickrAccount) is not polluted with any Hymanson annotations.

它仍然没有我希望的那么优雅，但至少我摆脱了所有丑陋的演员阵容。此解决方案的另一个优点是，我的域类 ( FlickrAccount) 不会被任何 Hymanson 注释污染。

Based on @Micha? Ziober's answer, I decided to use the - in my opinion - most straight forward solution. Using a @JsonDeserializeannotation with a custom deserializer:

基于@Micha？Ziober 的回答，我决定使用 - 在我看来 - 最直接的解决方案。使用@JsonDeserialize带有自定义反序列化器的注释：

@JsonDeserialize( using = FlickrAccountDeserializer.class )
public class FlickrAccount {
    ...
}

But the deserializer does not use any internal classes, just the JsonNodeas above:

但是反序列化器不使用任何内部类，就像JsonNode上面一样：

class FlickrAccountDeserializer extends JsonDeserializer<FlickrAccount> {
    @Override
    public FlickrAccount deserialize(JsonParser jp, DeserializationContext ctxt) throws 
            IOException, JsonProcessingException {
        FlickrAccount account = new FlickrAccount();
        JsonNode node = jp.readValueAsTree();
        JsonNode user = node.get("user");
        account.setId(user.get("id").asText());
        account.setUsername(user.get("username").get("_content").asText());
        return account;
    }
}

回答by sendon1982

You can also use SimpleModule.

您还可以使用 SimpleModule。

    SimpleModule module = new SimpleModule();
    module.setDeserializerModifier(new BeanDeserializerModifier() {
    @Override public JsonDeserializer<?> modifyDeserializer(
        DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer) {
        if (beanDesc.getBeanClass() == YourClass.class) {
            return new YourClassDeserializer(deserializer);
        }

        return deserializer;
    }});

    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(module);
    objectMapper.readValue(json, classType);