SPRING.md

Spring and kjson

Default Spring Serialization and Deserialization

Many users will seek to use kjson in conjunction with the Spring Framework.

If a class of the following form is present in the classpath scanned by Spring, it will be used by the framework as the default JSON serialization and deserialization function for Spring Boot etc.

package my.example

import java.io.Reader
import java.io.Writer
import java.lang.reflect.Type

import org.springframework.http.MediaType
import org.springframework.http.converter.json.AbstractJsonHttpMessageConverter
import org.springframework.stereotype.Service

import io.kjson.JSONConfig
import io.kjson.JSONString
import io.kjson.JSONStringify.appendJSON
import io.kjson.deserialize

import my.custom.type.Money

@Service
class JSONConverter : AbstractJsonHttpMessageConverter() {

    override fun canRead(mediaType: MediaType?): Boolean {
        return mediaType != null && mediaType.equalsTypeAndSubtype(MediaType.APPLICATION_JSON)
    }

    override fun canWrite(mediaType: MediaType?): Boolean {
        return mediaType != null && mediaType.equalsTypeAndSubtype(MediaType.APPLICATION_JSON)
    }

    override fun readInternal(resolvedType: Type, reader: Reader): Any? {
        return JSON.parse(reader.readText()).deserialize(resolvedType, config)
    }

    override fun writeInternal(o: Any, type: Type?, writer: Writer) {
        writer.appendJSON(o, config)
    }

    companion object {

        /**
         * JSONConfig containing specific configuration for this application.
         *
         * It is placed in a companion object to allow it to be used from other parts of the application, e.g.
         *     val event = jsonString.parseJSON<Event>(JSONConverter.config)
         */
        val config = JSONConfig {

            allowExtra = true // example configuration setting

            toJSONString<Money>() // example custom serialization

            fromJSON { json -> // example custom deserialization
                require(json is JSONString) { "JSON representation of Money must be string" }
                Money.of(json.value)
            }

        }

    }

}

This class is provided as documentation rather than as a source file because it would not be practical for this project to include the dependencies required to resolve the Spring references.

UPDATE: the kjson-spring library now provides a simple way to integrate with Spring.

2022-09-05