This is material where I personally jot down things I don't know and briefly organize what I come to learn. If you know something among the unanswered questions, please leave a comment. Thank you.

Full Q&A List

[Answered]

1. @JsonInclude(Include.NON_NULL)?

This annotation excludes class fields that are null from being serialized to JSON. In the code above, the stringValue variable is not stored in the JSON.

Terminology

• The task of converting a Java object to JSON is referred to as serialize, and JSON -> object is called deserialize

Reference

• http://multifrontgarden.tistory.com/172

2. @JsonIgnore?

This is an annotation you declare above a variable when you don't want to include that field during serialization. In this example, the @JsonIgnore annotation was applied because the password must not be present when fetching a domain object through JPA.

Reference

• http://eglowc.tistory.com/28

3. @JsonIgnoreProperties(ignoreUnknown = true)?

This is an annotation that ignores the Exception that occurs when a property that does not exist on the object is included in the JSON.

Reference

• https://www.javacodegeeks.com/2018/01/ignore-unknown-properties-parsing-json-java-jackson-jsonignoreproperties-annotation-example.html

4. What happens if you set allowGetters to true in @JsonIgnoreProperties?

When specifying the properties to ignore with @JsonIgnoreProperties, setting allowGetters to true means that the specified fields are applied for JSON serialization (Object -> JSON), but are excluded for deserialization (JSON -> Object).

Reference

• https://www.concretepage.com/jackson-api/jackson-jsonignore-jsonignoreproperties-and-jsonignoretype#allowGetters

5. What do serialization and deserialization mean in Jackson?

• Jackson
  • Serialization
    • Converting a Java Object -> Jackson JSON.
  • Deserialization
    • Converting Jackson JSON -> Java Object
• Java (for reference)
  • Serialization
    • Java Object -> byte form
  • Deserialization
    • byte form -> Java Object

Reference

• Jackson

  • https://homoefficio.github.io/2016/11/19/%EC%A1%B0%EA%B8%88%EC%9D%80-%EC%8B%A0%EA%B2%BD%EC%8D%A8%EC%A4%98%EC%95%BC-%ED%95%98%EB%8A%94-Jackson-Custom-Deserialization/
  • https://thepracticaldeveloper.com/2018/07/31/java-and-json-jackson-serialization-with-objectmapper/

• Java

• https://nesoy.github.io/articles/2018-04/Java-Serialize

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[Unanswered Questions]

- What is the difference between @DateTimeFormat vs @JsonFormat?

• DateTimeFormat : DateTimeFormat
• JsonFormat : jackson

- @JsonTypInfo, @JsonSubTypes?

Reference

• https://www.slipp.net/questions/442
• https://seongtak-yoon.tistory.com/70

- @JsonManagedReference

- @JsonBackReference

- What are @JsonIdentityInfo and @JsonIdentityReference?

• When querying data from entities connected with @OneToMany, @ManyToOne, an Infinite recursion JsonMappingException occurs
• Solution
  • Jackson 1/6+
    • Use @JsonManagedReference, @JsonBackReference
  • Jackson 2.0+
    • Use @JsonIdentityInfo