Jackson处理Optional时遇到问题的解决与分析

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    public String username;
    public Optional<String> nickname;
}

User user = new User("jalon", Optional.of("xiaowang"));
ObjectMapper objectMapper = new ObjectMapper();
String str = objectMapper.writeValueAsString(user);
System.out.println(str);

{"username":"jalon","nickname":"xiaowang"}

public final class Optional<T> {
    private final T value;
    public T get() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }

    public boolean isPresent() {
        return value != null;
    }

    @Override
    public String toString() {
        return value != null
            ? String.format("Optional[%s]", value)
            : "Optional.empty";
    }
}

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jdk8</artifactId>
    <version>2.12.5</version>
</dependency>

User user = new User("jalon", Optional.of("xiaowang"));
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new Jdk8Module());
String str = objectMapper.writeValueAsString(user);
System.out.println(str);