lovelyefyyucui / kotlin-in-action-2e-jkid

Sample project accompanying the second edition of "Kotlin in Action". JSON serialization/deserialization library for Kotlin data classes

Kotlin in Action 2e: JKid Implementation

Note This project accompanies Chapter 12, "Introspecting Kotlin Code" of the Kotlin in Action book. It is designed as an educational resource to illustrate concepts of working with annotations and reflections in Kotlin. For production applications that require JSON serialization and deserialization, take a look at kotlinx.serialization.

JKid is a case study of how to build a simple JSON serialization/deserialization library for Kotlin data classes. To serialize or deserialize an object use the serialize and deserialize functions.

"Declaring and Applying Annotations" of chapter 12 describes annotations in Kotlin, and also shows how to use the library and how to tune it with annotations. You can find examples for this section in the folder test/kotlin/examples. Five examples correspond to five subsections accordingly. The file kotlin/Annotations.kt contains the declarations of discussed annotations.

The section "Reflection: Introspecting Kotlin Objects at Runtime" of the book describes the implementation of serializer and deserializer. The files main/kotlin/serialization/Serializer.kt and main/kotlin/deserialization/Deserializer.kt contain the source code.

Exercises

We highly encourage you to do the following exercises after reading the text. Solving these exercises will help you to understand the concepts better and lets you practice right away.

DateFormat support

This first exercise can be started after reading the description of the serializer, specifically, after finishing the section "Customizing Serialization with Annotations."

Support the annotation DateFormat, which allows you to annotate a date property with @DateFormat("dd-MM-yyyy"), specifying the date format as an argument. A unit test example that also illustrates its usage is in the file test/kotlin/exercise/DateFormatAnnotation.kt. Remove @Ignore from the test DateFormatTest and make the test pass. The declaration of the annotation is in the file main/kotlin/exercise/DateFormat.kt. The solution to this exercise can be found in the branch solution-date-format.

Support for maps as property values

The second exercise is intended to be started after reading the whole chapter.

Currently, JKid only supports objects and collections as property values. Add support for the serialization and deserialization of maps as property values. You can find an unit test that serves as an example in test/kotlin/exercise/Map.kt. Remove @Ignore from the test MapTest and make it pass.

To support deserialization of maps, create a class MapSeed similar to ObjectSeed and collection seeds. The function createSeedForType should now return an instance of MapSeed if a map is expected. The example solution can be found in the branch solution-map.