Read JSON file to Object Kotlin

Question

How can I read JSON file and then put this into objects define in @Document - model for MongoDB. I'm looking for something like jackson object mapper in Java. It doesn't work here becouse Documen - model don't have empty constructor.

@Document(collection = "XXX")
 class Room(@Id
            private val id: String?,
            private val name: String){there is toString() method}


class Application{

@Bean
fun imageProcess(repo: MongoRepository) = CommandLineRunner {

    println("----------------Save customers!")


    for (room in read("C:/Users/Desktop/new.json")) {
        repo.save(room)
    }

}

val mapper = ObjectMapper().registerModule(KotlinModule())

fun read(path: String): Array<Room>? {

var temp: Array<Room>? = null
try {
    temp = mapper.readValue(File(path), Array<Room>::class.java)
} catch (ex: IOException) {
    ex.printStackTrace()
}

return temp

}

Could you provide the content of the JSON file and the error message? — Rene
– Rene, Commented Oct 18, 2018 at 20:33

Rene · Accepted Answer · 2018-10-18 18:22:19Z

2

Jackson should work together with this module: https://github.com/FasterXML/jackson-module-kotlin

"Previously a default constructor must have existed on the Kotlin object for Jackson to deserialize into the object. With this module, single constructor classes can be used automatically, and those with secondary constructors or static factories are also supported."

import com.fasterxml.jackson.module.kotlin.*

data class MyStateObject(val name: String, val age: Int)

...
val mapper = jacksonObjectMapper()

val state = mapper.readValue<MyStateObject>(json)
// or
val state: MyStateObject = mapper.readValue(json)
// or
myMemberWithType = mapper.readValue(json)

answered Oct 18, 2018 at 18:22

Rene

6,34820 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Anytram Over a year ago

@Document's syntax tells that variables must be as class parametres. And compiler don't let me create constructor. :( So how can I rewrite my model to could have deafault constructor?

Rene Over a year ago

if your JSON looks like {"id":"1", "name":"John"} you don't need a default constructor. Just add the module to your project and adapt the example to your class.

Collectives™ on Stack Overflow

Read JSON file to Object Kotlin

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related