oh, right.

thanks!

yep!

i got the hang of it!

mapper.readTree(json).at("/books").forEach {
      it.fields().forEach {
        println("${it.key} to ${it.value}")
      }
      println("--")
    }

(i turned “book” into “books”, and into an array of objects! :))

yep, that’ll do it

hey, sorry, but i got one more question – doing the oposite. how can i save a bunch of values to the json file in a similar format? where i cna do something like

<http://mapper.at|mapper.at>("/books/$counter/$key") = value

i’ve figured out the write tree, but im a bit stuck now

I would create some data classes with the structure you want.

Data classes are pretty succinct, and probably a lot less code than creating the tree by hand.

i do have a data class:``` package id.or.jisedu.repo data class Book( val title: String, val title_long: String? = null, val isbn: String? = null, val isbn13: String? = null, val dewey_decimal: String? = null, val format: String? = null, val publisher: String? = null, val language: String? = null, val date_published: String? = null, val edition: String? = null, val pages: String? = null, val binding: String? = null, val dimensions: String? = null, val overview: String? = null, val excerpt: String? = null, val synopsys: String? = null, val image: String? = null, val authors: List<String>, val subjects: List<String>? = null, var id: Long? = null, var amount: Int = 1 ) ```

BTW as a general rule I annotate my json-related data class fields with

@JsonProperty

to define the JSON name so that I can freely rename fields without affecting serialization. You might wish to do the same. Or not, ymmv.

just, most of the time, they are null

so it makes it a bit um - more difficult

If you want to exclude the nulls, you can sprinkle the appropriate Jackson annotations around

How so?

Book(binding="whatever", authors=listOf())

well, it makes it more difficult to store into json

is what i meant

any chance u can share the jackson annotations?

Hm, I’m not sure what you mean re: more difficult

@JsonInclude(Include.NON_NULL)

is what you want I think

oh, and i just annotate teh data class, not each property?

yes

though I would do

@JsonProperty("date_published")

, for instance, so you can have more idiomatic

datePublished

field name

okay

any chance i can do something similar for turning the json object into a book?

so i can only set the values that exist, and ignore the others?

Yes, just deserialize your json into that data class.

ok, let me try that

reader.forType(Book::class.java).readValue(someInputStreamOrWhatever)

I think is the syntax (from memory, so it probably won’t quite compile)

what is the object

reader

?