如何從自訂解串器呼叫 Jackson 的預設解串器？

從 Jackson 中的自訂解串器呼叫預設解串器

問題：

在 Jackson中建立一個自訂解串器，允許在應用自訂之前存取預設反序列化器以預先填充物件

程式碼:

public class UserEventDeserializer extends StdDeserializer<user> {

    public UserEventDeserializer() {
        super(User.class);
    }

    @Override
    public User deserialize(JsonParser jp, DeserializationContext ctxt)
        throws IOException, JsonProcessingException {
        
        // Line causing UnsupportedOperationException:
        User deserializedUser = super.deserialize(jp, ctxt, new User()); 
    }
}</user>

解:

實作BeanDeserializerModifier為特定的物件註冊自訂反序列化器類別。

代碼:

public class UserEventDeserializer extends StdDeserializer<user> implements ResolvableDeserializer {

    private final JsonDeserializer> defaultDeserializer;

    public UserEventDeserializer(JsonDeserializer> defaultDeserializer) {
        super(User.class);
        this.defaultDeserializer = defaultDeserializer;
    }

    @Override
    public User deserialize(JsonParser jp, DeserializationContext ctxt)
        throws IOException, JsonProcessingException {
        
        User deserializedUser = (User) defaultDeserializer.deserialize(jp, ctxt);

        // Special logic

        return deserializedUser;
    }

    // Required when modifying BeanDeserializer
    @Override
    public void resolve(DeserializationContext ctxt) throws JsonMappingException {
        ((ResolvableDeserializer) defaultDeserializer).resolve(ctxt);
    }

    public static void main(String[] args) throws Exception {
        SimpleModule module = new SimpleModule();
        module.setDeserializerModifier(new BeanDeserializerModifier() {
            @Override
            public JsonDeserializer> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer> deserializer) {
                if (beanDesc.getBeanClass() == User.class)
                    return new UserEventDeserializer(deserializer);
                return deserializer;
            }
        });

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(module);
        User user = mapper.readValue(new File("test.json"), User.class);
    }
}</user>

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