====== Java Jackson JSON Library ======
  * [[java:jackson:jsonfilter|Jackson JsonFilter]]
  * [[java:jackson:squiggly|Squiggly]]
  * [[http://www.baeldung.com/jackson|Jackson Tutorial]]
  * [[http://www.baeldung.com/jackson-ignore-properties-on-serialization|Jackson Ignore Properties on Marshalling]]
  * [[https://github.com/FasterXML/jackson-module-afterburner|Jackson module afterburner]] Jackson 직렬화/역직렬화 성능 향상
  * [[https://github.com/FasterXML/jackson-datatype-hibernate|Jackson datatype hibernate]] Hibernate 데이터를 JSON으로 변환할 때 Lazy loading으로 인해 발생하는 문제 해결
  * [[http://wiki.fasterxml.com/JacksonUpgradeFrom19To20|JacksonUpgradeFrom19To20]]
  * [[http://www.cowtowncoder.com/blog/archives/2011/09/entry_461.html|Advanced filtering with Jackson, Json Filters]]
  * [[http://www.cowtowncoder.com/blog/archives/2011/02/entry_443.html|Every day Jackson usage, part 3: Filtering properties]]
  * [[http://www.baeldung.com/jackson-annotations|A Guide to Jackson Annotations]]
  * [[http://www.baeldung.com/java-json|JSON in Java]]


===== @JsonView =====
  * 객체의 필드를 선별적으로 직렬화 할 수 있다.
  * ''@Annotation'' 지옥이 필쳐질 수도 있다.
  * [[http://wiki.fasterxml.com/JacksonJsonViews|JacksonJsonViews]]
  * [[http://stackoverflow.com/questions/5772304/using-jsonview-with-spring-mvc|Using @JsonView with Spring MVC]]
  * Spring 4.1 부터 ''@JsonView'', [[https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/converter/json/MappingJacksonValue.html|Spring MappingJacksonViewValue]] 지원
  * [[https://spring.io/blog/2014/12/02/latest-jackson-integration-improvements-in-spring|Latest Jackson integration improvements in Spring]]
  * [[https://www.baeldung.com/jackson-json-view-annotation|Jackson JSON Views | Baeldung]]
===== @JsonCreator =====
  * 해당 클래스 JSON 문자열을 받아서 객체를 생성할 때 변환기를 직접 만들고자 할 때 구현한다.
  * [[https://fasterxml.github.io/jackson-annotations/javadoc/2.7/com/fasterxml/jackson/annotation/JsonCreator.html|@JsonCreator]]
  * [[https://grokonez.com/java/jackson-jsoncreator-example-deserialize-jsoncreator|Jackson @JsonCreator example - Deserialize with @JsonCreator - grokonez]]
<code java>
public class Customer {
    private String id;
    private String name;
    private String address;
 
    public Customer() {
    }
 
    @JsonCreator
    public Customer(
            @JsonProperty("id") String id, 
            @JsonProperty("fullname") String name,
            @JsonProperty("location") String address) {
        System.out.println("run constructor...");
        this.id = id;
        this.name = name;
        this.address = address;
    }
 
    @Override
    public String toString() {
        return "Customer [id=" + id + ", name=" + name + ", address=" + address + "]";
    }
}
</code>
===== Performance =====
  * [[http://wiki.fasterxml.com/JacksonBestPracticesPerformance|Jackson Best Practice Performance]]

===== Config 설정 =====
<code java>
ObjectMapper objectMapper = new ObjectMapper();

objectMapper
  // 모르는 property에 대해 무시하고 넘어간다. DTO의 하위 호환성 보장에 필요하다.
  .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

  // ENUM 값이 존재하지 않으면 null로 설정한다. Enum 항목이 추가되어도 무시하고 넘어가게 할 때 필요하다.
  .configure(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL, true);
  // 시간을 timestamp 숫자가 아닌, 문자열로 포맷팅한다. 기본 ISO 포맷
  .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
</code>


===== Bidirectional Relation 양방향 관계 =====
  * [[http://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion|Jackson - Bidirectional Relationships]]
  * [[https://fasterxml.github.io/jackson-annotations/javadoc/2.6/com/fasterxml/jackson/annotation/JsonIgnoreProperties.html|@JsonIgnoreProperties]]
  * [[https://fasterxml.github.io/jackson-annotations/javadoc/2.6/com/fasterxml/jackson/annotation/JsonIdentityInfo.html|@JsonIdentityInfo]] 동일 ID에 대해 중복 출력 방지
  * [[https://github.com/FasterXML/jackson-datatype-hibernate|Jackson Datatype Hibernate]] Hibernate Lazy loading 필드를 Jackson 직렬화 대상에서 제외

===== Pretty Print =====
<code java>
// 전역설정
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

// Writer 당 설정
new ObjectMapper()
.writer()
.withDefaultPrettyPrinter()
.writeValueAsString(객체);
</code>

===== setDateFormat 주의 =====
    * **''simpleDateFormat(), dateFormat()''을 설정하면 ''ObjectMapper''가 non-thread-safe 하게 돼 버린다.** 하지말고, ''java.util.Date''도 사용하지 말 것.

===== Hibernate =====
  * [[java:hibernate|Hibernate]] 사용시 LazyLoading 문제 해소 모듈
  * Lazy Loading 필드일 경우 그냥 null 처리하고 넘어간다. 그러나 이미 로딩이 돼 있으면 직렬화 한다.
  * Lazy Loading 대상 필드의 값을 가져오는 getter가 존재한다면 ''@JsonIgnore''를 하거나 미리 로딩하지 않으면 다시 Lazy Loading Exception 이 발생한다.
  * [[https://github.com/FasterXML/jackson-datatype-hibernate|jackson-datatype-hibernate]]
  * 양방향 관계에 대해 [[https://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion|Jackson - Bidirectional Relationships JPA Entity 직렬화 방법들]] 참조<code java>
public class User {
    public int id;
    public String name;
 
    // @JsonBackReference 애노테이션이 붙으면 직렬화를 하지 않는다.
    @JsonBackReference
    public List<Item> userItems;
}

public class Item {
    public int id;
    public String itemName;
 
    @JsonManagedReference
    public User owner;
}
</code><code json>
{
 "id":2,
 "itemName":"book",
 "owner":
    {
        "id":1,
        "name":"John"
    }
}
</code>
  * ''@JsonIdentityInfo'' 사용시에는 양방향 관계에서 Entity Id 만 직렬화해준다.

===== @JsonRawValue =====
  * [[https://www.logicbig.com/tutorials/misc/jackson/json-raw-value.html|Jackson JSON - Using @JsonRawValue to serialize property as it is]]
  * String 필드게 JSON 문자열이 저장돼 있을 경우 이를 JSON 으로 간주하고 리턴
  * 직렬화에서는 작동하지만 역직렬화에서는 작동하지 않는다.
  * [[https://stackoverflow.com/questions/4783421/how-can-i-include-raw-json-in-an-object-using-jackson|java - How can I include raw JSON in an object using Jackson? - Stack Overflow]]


===== @JsonInclude =====
  * [[https://www.baeldung.com/jackson-ignore-null-fields|Ignore Null Fields with Jackson | Baeldung]]
  * ''@JsonInclude(INclude.NON_NULL)'' : null인경우 아예 렌더링을 하지 않는다.
  * [[https://alwayspr.tistory.com/31|[Jackson] JsonInclude 속성에 대해 알아보자.]]
===== JsonNodeFactory =====
  * [[https://fasterxml.github.io/jackson-databind/javadoc/2.1.0/com/fasterxml/jackson/databind/node/JsonNodeFactory.html|JsonNodeFactory]]
  * ''JsonNodeFactory.instance.objectNode()'' 를 통해 원하는 형태의 JSON 을 생성할 수 있다.
  * [[java:json|Java JSON]]

<code java>
JsonNodeFactory.instance.objectNode().put("id", 123L)
            .put("name", "JSONNODE")
            .put("age", 12)
            .toString();
</code>

===== Java 8 =====
  * [[https://github.com/FasterXML/jackson-modules-java8|jackson modules java8]]
  * Jackson 2 까지는 다음과 같이 모듈들을 추가해줘야 하며 Jackson 3 부터는 Java 8이 필수라서 기본 지원이 된다.

<code>
<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-module-parameter-names</artifactId>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jdk8</artifactId>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
</dependency>
</code>

<code java>
// Up to Jackson 2.9: (but not with 3.0)
ObjectMapper mapper = new ObjectMapper()
   .registerModule(new ParameterNamesModule())
   .registerModule(new Jdk8Module())
   .registerModule(new JavaTimeModule()); // new module, NOT JSR310Module

</code>
  * ''SerializationFeature.WRITE_DATES_AS_TIMESTAMPS: false'' 설정이 있어야만 ''LocalDateTime'' 등을 ''ISO_LOCAL_DATE_TIME'' format 등으로 직렬화한다.

===== Jackson 2.10 부터 ObjectMapper 생성 방식 변경됨 =====
<code java>
JsonMapper objectMapper = JsonMapper.builder()
    .addModules(new ParameterNamesModule(), new Jdk8Module(), new JavaTimeModule())
    // 모르는 property 를 역직렬화 할 때 오류없이 무시하게 한다.
    .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
    // 모르는 ENUM 값을 역직렬화 할 때 null로 취급하게 한다.
    .configure(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL, true)
    // 시간 관련 객체(LocalDateTime, java.util.Date)를 직렬화 할 때 timestamp 숫자값이 아닌 포맷팅 문자열로 한다.
    .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
    // 숫자를 문자로 직렬화하기, BigDecimal 보호?
    .enable(JsonWriteFeature.WRITE_NUMBERS_AS_STRINGS)
    .defaultTimeZone(TimeZone.getDefault())
    .defaultLocale(Locale.getDefault())
    .build();
</code>

===== Java 16 Record =====
  * [[https://carloschac.in/2021/03/04/jacksonrecords/|💾 Java Records 💿 with Jackson 2.12 | Carlos Chacin]]
  * Jackson >= 2.12.0 부터 [[java:16|Java 16]] 레코드 사용가능.
===== 참고 =====
  * [[http://www.baeldung.com/jackson-serialize-dates|Jackson Date]]<code java>
    @JsonFormat
      (shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd hh:mm:ss")
    private Date createdAt;
</code>
  * [[http://www.baeldung.com/jackson-advanced-annotations|More Jackson Annotations]]
  * [[http://www.baeldung.com/jackson-annotations|Jackson Annotation Examples | Baeldung]]
  * [[http://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion|Jackson - Bidirectional Relationships | Baeldung]]
  * [[https://dzone.com/articles/jackson-annotations-for-json-part-2-serialization|Jackson Annotations for JSON (Part 2): Serialization - DZone Java]]
  * [[https://www.javacodegeeks.com/2018/01/ignore-unknown-properties-parsing-json-java-jackson-jsonignoreproperties-annotation-example.html|How to ignore unknown properties while parsing JSON in Java - Jackson @JsonIgnoreProperties Annotation Example | Java Code Geeks - 2018]]
  * [[https://www.baeldung.com/jackson-serialize-enums|How To Serialize Enums as JSON Objects with Jackson | Baeldung]]
  * [[https://www.baeldung.com/jackson-mapping-dynamic-object|Mapping a Dynamic JSON Object with Jackson | Baeldung]]
  * [[https://www.baeldung.com/jackson-annotations|Jackson Annotation Examples | Baeldung]]
  * [[https://cheese10yun.github.io/jackson-annotation/|Jackson 어노테이션 사용법(1) - Yun Blog]]
  * [[https://dzone.com/articles/jackson-json-and-the-proper-handling-of-unknown-fi|Jackson, JSON and the Proper Handling of Unknown Fields in APIs - DZone Java]]
  * [[https://www.baeldung.com/jackson-ignore-null-fields|Ignore Null Fields with Jackson | Baeldung]]
  * [[https://www.baeldung.com/jackson-field-serializable-deserializable-or-not|Jackson - Decide What Fields Get (De)Serialized | Baeldung]]
  * [[https://www.baeldung.com/jackson-deserialization|Getting Started with Deserialization in Jackson | Baeldung]]