I'm receiving a quite deep JSON object string from a service which I must parse to a JSON object and then map it to classes.
How can I transform a JSON string to object in Kotlin?
After that the mapping to the respective classes, I was using StdDeserializer from Jackson. The problem arises at the moment the object had properties that also had to be deserialized into classes. I was not able to get the object mapper, at least I didn't know how, inside another deserializer.
Preferably, natively, I'm trying to reduce the number of dependencies I need so if the answer is only for JSON manipulation and parsing it'd be enough.
There is no question that the future of parsing in Kotlin will be with kotlinx.serialization. It is part of Kotlin libraries. Version kotlinx.serialization 1.0 is finally released
https://github.com/Kotlin/kotlinx.serialization
import kotlinx.serialization.*
import kotlinx.serialization.json.JSON
#Serializable
data class MyModel(val a: Int, #Optional val b: String = "42")
fun main(args: Array<String>) {
// serializing objects
val jsonData = JSON.stringify(MyModel.serializer(), MyModel(42))
println(jsonData) // {"a": 42, "b": "42"}
// serializing lists
val jsonList = JSON.stringify(MyModel.serializer().list, listOf(MyModel(42)))
println(jsonList) // [{"a": 42, "b": "42"}]
// parsing data back
val obj = JSON.parse(MyModel.serializer(), """{"a":42}""")
println(obj) // MyModel(a=42, b="42")
}
You can use this library https://github.com/cbeust/klaxon
Klaxon is a lightweight library to parse JSON in Kotlin.
Without external library (on Android)
To parse this:
val jsonString = """
{
"type":"Foo",
"data":[
{
"id":1,
"title":"Hello"
},
{
"id":2,
"title":"World"
}
]
}
"""
Use these classes:
import org.json.JSONObject
class Response(json: String) : JSONObject(json) {
val type: String? = this.optString("type")
val data = this.optJSONArray("data")
?.let { 0.until(it.length()).map { i -> it.optJSONObject(i) } } // returns an array of JSONObject
?.map { Foo(it.toString()) } // transforms each JSONObject of the array into Foo
}
class Foo(json: String) : JSONObject(json) {
val id = this.optInt("id")
val title: String? = this.optString("title")
}
Usage:
val foos = Response(jsonString)
You can use Gson .
Example
Step 1
Add compile
compile 'com.google.code.gson:gson:2.8.2'
Step 2
Convert json to Kotlin Bean(use JsonToKotlinClass)
Like this
Json data
{
"timestamp": "2018-02-13 15:45:45",
"code": "OK",
"message": "user info",
"path": "/user/info",
"data": {
"userId": 8,
"avatar": "/uploads/image/20180115/1516009286213053126.jpeg",
"nickname": "",
"gender": 0,
"birthday": 1525968000000,
"age": 0,
"province": "",
"city": "",
"district": "",
"workStatus": "Student",
"userType": 0
},
"errorDetail": null
}
Kotlin Bean
class MineUserEntity {
data class MineUserInfo(
val timestamp: String,
val code: String,
val message: String,
val path: String,
val data: Data,
val errorDetail: Any
)
data class Data(
val userId: Int,
val avatar: String,
val nickname: String,
val gender: Int,
val birthday: Long,
val age: Int,
val province: String,
val city: String,
val district: String,
val workStatus: String,
val userType: Int
)
}
Step 3
Use Gson
var gson = Gson()
var mMineUserEntity = gson?.fromJson(response, MineUserEntity.MineUserInfo::class.java)
Not sure if this is what you need but this is how I did it.
Using import org.json.JSONObject :
val jsonObj = JSONObject(json.substring(json.indexOf("{"), json.lastIndexOf("}") + 1))
val foodJson = jsonObj.getJSONArray("Foods")
for (i in 0..foodJson!!.length() - 1) {
val categories = FoodCategoryObject()
val name = foodJson.getJSONObject(i).getString("FoodName")
categories.name = name
}
Here's a sample of the json :
{"Foods": [{"FoodName": "Apples","Weight": "110" } ]}
I personally use the Jackson module for Kotlin that you can find here: jackson-module-kotlin.
implementation "com.fasterxml.jackson.module:jackson-module-kotlin:$version"
As an example, here is the code to parse the JSON of the Path of Exile skilltree which is quite heavy (84k lines when formatted) :
Kotlin code:
package util
import com.fasterxml.jackson.databind.DeserializationFeature
import com.fasterxml.jackson.module.kotlin.*
import java.io.File
data class SkillTreeData( val characterData: Map<String, CharacterData>, val groups: Map<String, Group>, val root: Root,
val nodes: List<Node>, val extraImages: Map<String, ExtraImage>, val min_x: Double,
val min_y: Double, val max_x: Double, val max_y: Double,
val assets: Map<String, Map<String, String>>, val constants: Constants, val imageRoot: String,
val skillSprites: SkillSprites, val imageZoomLevels: List<Int> )
data class CharacterData( val base_str: Int, val base_dex: Int, val base_int: Int )
data class Group( val x: Double, val y: Double, val oo: Map<String, Boolean>?, val n: List<Int> )
data class Root( val g: Int, val o: Int, val oidx: Int, val sa: Int, val da: Int, val ia: Int, val out: List<Int> )
data class Node( val id: Int, val icon: String, val ks: Boolean, val not: Boolean, val dn: String, val m: Boolean,
val isJewelSocket: Boolean, val isMultipleChoice: Boolean, val isMultipleChoiceOption: Boolean,
val passivePointsGranted: Int, val flavourText: List<String>?, val ascendancyName: String?,
val isAscendancyStart: Boolean?, val reminderText: List<String>?, val spc: List<Int>, val sd: List<String>,
val g: Int, val o: Int, val oidx: Int, val sa: Int, val da: Int, val ia: Int, val out: List<Int> )
data class ExtraImage( val x: Double, val y: Double, val image: String )
data class Constants( val classes: Map<String, Int>, val characterAttributes: Map<String, Int>,
val PSSCentreInnerRadius: Int )
data class SubSpriteCoords( val x: Int, val y: Int, val w: Int, val h: Int )
data class Sprite( val filename: String, val coords: Map<String, SubSpriteCoords> )
data class SkillSprites( val normalActive: List<Sprite>, val notableActive: List<Sprite>,
val keystoneActive: List<Sprite>, val normalInactive: List<Sprite>,
val notableInactive: List<Sprite>, val keystoneInactive: List<Sprite>,
val mastery: List<Sprite> )
private fun convert( jsonFile: File ) {
val mapper = jacksonObjectMapper()
mapper.configure( DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT, true )
val skillTreeData = mapper.readValue<SkillTreeData>( jsonFile )
println("Conversion finished !")
}
fun main( args : Array<String> ) {
val jsonFile: File = File( """rawSkilltree.json""" )
convert( jsonFile )
JSON (not-formatted): http://filebin.ca/3B3reNQf3KXJ/rawSkilltree.json
Given your description, I believe it matches your needs.
GSON is a good choice for Android and Web platform to parse JSON in a Kotlin project. This library is developed by Google.
https://github.com/google/gson
1. First, add GSON to your project:
dependencies {
implementation 'com.google.code.gson:gson:2.8.9'
}
2. Now you need to convert your JSON to Kotlin Data class:
Copy your JSON and go to this(https://json2kt.com) website and paste your JSON to Input Json box. Write package(ex: com.example.appName) and Class name(ex: UserData) in proper box. This site will show live preview of your data class below and also you can download all classes at once in a zip file.
After downloading all classes extract the zip file & place them into your project.
3. Now Parse like below:
val myJson = """
{
"user_name": "john123",
"email": "john#example.com",
"name": "John Doe"
}
""".trimIndent()
val gson = Gson()
var mUser = gson.fromJson(myJson, UserData::class.java)
println(mUser.userName)
Done :)
This uses kotlinx.serialization like Elisha's answer. Meanwhile the project is past version 1.0 so the API has changed. Note that e.g. JSON.parse was renamed to Json.decodeFromString. Also it is imported in gradle differently starting in Kotlin 1.4.0:
dependencies {
implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.0"
}
apply plugin: 'kotlinx-serialization'
Example usage:
import kotlinx.serialization.Serializable
import kotlinx.serialization.json.Json
import kotlinx.serialization.decodeFromString
import kotlinx.serialization.encodeToString
#Serializable
data class Point(val x: Int, val y: Int)
val pt = Json.decodeFromString<Point>("""{"y": 1, "x": 2}""")
val str = Json.encodeToString(pt) // type can be inferred!
val ilist = Json.decodeFromString<List<Int>>("[-1, -2]")
val ptlist = Json.decodeFromString<List<Point>>(
"""[{"x": 3, "y": 4}, {"x": 5, "y": 6}]"""
)
You can use nullable types (T?) for both nullable and optional fields:
#Serializable
data class Point2(val x: Int, val y: Int? = null)
val nlist = Json.decodeFromString<List<Point2>>(
"""[{"x": 7}, {"x": 8, "y": null}, {"x": 9, "y": 0}]"""
)
Kotlin's data class is a class that mainly holds data and has members, .toString() and other methods (e.g. destructuring declarations) automatically defined.
To convert JSON to Kotlin use http://www.json2kotlin.com/
Also you can use Android Studio plugin. File > Settings, select Plugins in left tree, press "Browse repositories...", search "JsonToKotlinClass", select it and click green button "Install".
After AS restart you can use it. You can create a class with File > New > JSON To Kotlin Class (JsonToKotlinClass). Another way is to press Alt + K.
Then you will see a dialog to paste JSON.
In 2018 I had to add package com.my.package_name at the beginning of a class.
First of all.
You can use JSON to Kotlin Data class converter plugin in Android Studio for JSON mapping to POJO classes (kotlin data class).
This plugin will annotate your Kotlin data class according to JSON.
Then you can use GSON converter to convert JSON to Kotlin.
Follow this Complete tutorial:
Kotlin Android JSON Parsing Tutorial
If you want to parse json manually.
val **sampleJson** = """
[
{
"userId": 1,
"id": 1,
"title": "sunt aut facere repellat provident occaecati excepturi optio
reprehenderit",
"body": "quia et suscipit\nsuscipit recusandae consequuntur expedita"
}]
"""
Code to Parse above JSON Array and its object at index 0.
var jsonArray = JSONArray(sampleJson)
for (jsonIndex in 0..(jsonArray.length() - 1)) {
Log.d("JSON", jsonArray.getJSONObject(jsonIndex).getString("title"))
}
Kotlin Serialization
Kotlin specific library by JetBrains for all supported platforms – Android, JVM, JavaScript, Native.
https://github.com/Kotlin/kotlinx.serialization
Moshi
Moshi is a JSON library for Android and Java by Square.
https://github.com/square/moshi
Jackson
https://github.com/FasterXML/jackson
Gson
Most popular but almost deprecated.
https://github.com/google/gson
JSON to Java
http://www.jsonschema2pojo.org/
JSON to Kotlin
IntelliJ plugin - https://plugins.jetbrains.com/plugin/9960-json-to-kotlin-class-jsontokotlinclass-
Parse JSON string to Kotlin object
As others recommend, Gson library is the simplest way!
If the File is in the Asset folder you can do like this, first add
dependencies {
implementation 'com.google.code.gson:gson:2.9.0'
}
then get a file from Asset:
jsonString = context.assets.open(fileName).bufferedReader().use { it.readText() }
then use Gson :
val gson = Gson()
val listPersonType = object : TypeToken<List<Person>>() {}.type
var persons: List<Person> = gson.fromJson(jsonFileString, listPersonType)
persons.forEachIndexed { idx, person -> Log.i("data", "> Item $idx:\n$person") }
Where Person is a Model/Data class, like this
data class Person(val name: String, val age: Int, val messages: List) {
}
If you prefer parsing JSON to JavaScript-like constructs making use of Kotlin syntax, I recommend JSONKraken, of which I am the author.
You can do things like:
val json: JsonValue = JsonKraken.deserialize("""{"getting":{"started":"Hello World"}}""")
println(JsonKraken.serialize(json)) //prints: {"getting":{"started":"Hello World"}}
println(json["getting"]["started"].cast<String>()) //prints: Hello World
Suggestions and opinions on the matter are much apreciated!
I created a simple Extention function to convert JSON string to model class
inline fun <reified T: Any> String.toKotlinObject(): T =
Gson().fromJson(this, T::class.java)
Usage method
stringJson.toKotlinObject<MyModelClass>()
http://www.jsonschema2pojo.org/
Hi you can use this website to convert json to pojo.
control+Alt+shift+k
After that you can manualy convert that model class to kotlin model class. with the help of above shortcut.
Seems like Kotlin does not have any built-in method as in many cases it just imports and implements some tools from Java. After trying lots of packages, finally this one worked reasonably. This fastjson from alibaba, which is very easy to use. Inside build gradle dependencies:
implementation 'com.alibaba:fastjson:1.1.67.android'
Inside your Kotlin code:
import com.alibaba.fastjson.JSON
var jsonDecodedMap: Map<String, String> =
JSON.parse(yourStringValueHere) as Map<String, String>;
Download the source of deme from here(Json parsing in android kotlin)
Add this dependency:
compile 'com.squareup.okhttp3:okhttp:3.8.1'
Call api function:
fun run(url: String) {
dialog.show()
val request = Request.Builder()
.url(url)
.build()
client.newCall(request).enqueue(object : Callback {
override fun onFailure(call: Call, e: IOException) {
dialog.dismiss()
}
override fun onResponse(call: Call, response: Response) {
var str_response = response.body()!!.string()
val json_contact:JSONObject = JSONObject(str_response)
var jsonarray_contacts:JSONArray= json_contact.getJSONArray("contacts")
var i:Int = 0
var size:Int = jsonarray_contacts.length()
al_details= ArrayList();
for (i in 0.. size-1) {
var json_objectdetail:JSONObject=jsonarray_contacts.getJSONObject(i)
var model:Model= Model();
model.id=json_objectdetail.getString("id")
model.name=json_objectdetail.getString("name")
model.email=json_objectdetail.getString("email")
model.address=json_objectdetail.getString("address")
model.gender=json_objectdetail.getString("gender")
al_details.add(model)
}
runOnUiThread {
//stuff that updates ui
val obj_adapter : CustomAdapter
obj_adapter = CustomAdapter(applicationContext,al_details)
lv_details.adapter=obj_adapter
}
dialog.dismiss()
}
})
Related
I am trying to show list of messages with different types of ViewHolders i.e. Text, ImageText, Video etc. I get a list of these objects from API somewhat in this format:
{
"message":"success",
"total_pages":273,
"current_page":1,
"page_size":10,
"notifications":[
{
"id":4214,
"notification_message":"test notification 1",
"meta_data":{
"messageId":"19819189",
"viewHolderType":"textOnly",
"body":{
"time":"10-06-21T02:31:29,573",
"type":"notification",
"title":"Hi, Welcome to the NT experience",
"description":"This is the welcome message",
"read":true
}
}
},
{
"id":9811,
"notification_message":"test vss notification",
"meta_data":{
"messageId":"2657652",
"viewHolderType":"textWithImage",
"body":{
"time":"11-06-21T02:31:29,573",
"type":"promotions",
"title":"Your Package - Premium",
"description":"Thank you for subscribing to the package. Your subscription entitles you to Premium 365 Days Plan (worth $76.61)",
"headerImage":"www.someurl.com/image.jpg",
"read":true
}
}
}
]
}
Now I have to parse this list from network module for client module which will use only the objects inside meta_data. To that end I have created following classes:
open class BaseMessageListItem
internal data class MessageListResponse(
#field:SerializedName("current_page")
val current_page: Int,
#field:SerializedName("notifications")
val notifications: List<MessageListItem>,
#field:SerializedName("message")
val message: String,
#field:SerializedName("page_size")
val page_size: Int,
#field:SerializedName("total_page")
val total_page: Int
)
internal data class MessageListItem(
#field:SerializedName(“id”)
val id: String,
#field:SerializedName("notification_message")
val notification_message: String,
#field:SerializedName("meta_data")
val meta_data: MessageListMetaDataItem,
)
internal data class MessageListMetaDataItem(
#field:SerializedName("messageId")
val messageId: String = "",
#field:SerializedName("viewHolderType")
val viewHolderType: String = "",
#field:SerializedName("body")
val body: BaseMessageListItem = BaseMessageListItem()
)
internal data class ImageMessageListItem(
#field:SerializedName("description")
val description: String,
#field:SerializedName("headerImage")
val headerImage: String,
#field:SerializedName("read")
val read: Boolean,
#field:SerializedName("time")
val time: String,
#field:SerializedName("title")
val title: String,
#field:SerializedName("type")
val type: String
): BaseMessageListItem()
internal data class TextMessageListItem(
#field:SerializedName("description")
val description: String,
#field:SerializedName("read")
val read: Boolean,
#field:SerializedName("time")
val time: String,
#field:SerializedName("title")
val title: String,
#field:SerializedName("type")
val type: String
): BaseMessageListItem()
The notifications>meta_data>body can be polymorphic. I have set of classes (for ImageItem, ImageWithTextItem, VideoItem etc) which extend to BaseMessageListItem.
private var runtimeTypeAdapterFactory: RuntimeTypeAdapterFactory<BaseMessageListItem> = RuntimeTypeAdapterFactory
.of(BaseMessageListItem::class.java, "viewHolderType")
.registerSubtype(ImageMessageListItem::class.java, MessageListItemTypes.TEXT_WITH_IMAGE.value)
.registerSubtype(TextMessageListItem::class.java, MessageListItemTypes.TEXT_ONLY.value)
private var gson: Gson = GsonBuilder()
.registerTypeAdapterFactory(runtimeTypeAdapterFactory)
.create()
I tried parsing it using viewHolderType in RuntimeTypeAdapterFactory but since it's not a property of BaseMessageListItem, it is not able to parse it.
Any one has any experience dealing with this type of JSON, please do share any pointers.
RuntimeTypeAdapterFactory requires the viewHolderType field to be put right into the body objects. In order to fix this, you have
either patch RuntimeTypeAdapterFactory (it is not even published as a compiled JAR, but rather still retains in the public repository as source code free to modify), or fix your class hierarchy to lift up the missing field because it can only work with fields on the same nest level.
internal var gson: Gson = GsonBuilder()
.registerTypeAdapterFactory(
RuntimeTypeAdapterFactory.of(BaseMessageListMetaDataItem::class.java, "viewHolderType")
.registerSubtype(TextWithImageMessageListMetaDataItem::class.java, "textWithImage")
.registerSubtype(TextOnlyMessageListMetaDataItem::class.java, "textOnly")
)
.create()
internal data class MessageListItem(
#field:SerializedName("meta_data")
val metaData: BaseMessageListMetaDataItem<*>?,
)
internal abstract class BaseMessageListMetaDataItem<out T>(
#field:SerializedName("viewHolderType")
val viewHolderType: String?,
#field:SerializedName("body")
val body: T?
) where T : BaseMessageListMetaDataItem.Body {
internal abstract class Body
}
internal class TextOnlyMessageListMetaDataItem
: BaseMessageListMetaDataItem<TextOnlyMessageListMetaDataItem.Body>(null, null) {
internal data class Body(
#field:SerializedName("title")
val title: String?
) : BaseMessageListMetaDataItem.Body()
}
internal class TextWithImageMessageListMetaDataItem
: BaseMessageListMetaDataItem<TextWithImageMessageListMetaDataItem.Body>(null, null) {
internal data class Body(
#field:SerializedName("title")
val title: String?,
#field:SerializedName("headerImage")
val headerImage: String?
) : BaseMessageListMetaDataItem.Body()
}
I might be understanding you wrong, but I would like to suggest a different approach. I am assuming you would like to assign to get a ViewHolder type directly from what you get in your API response.
There are two approaches I would like to suggest:
First, if it is possible to get the API response modified, I would suggest to change viewHolderType from a String to an Int so as you can be clear with your mapping and then you can directly compare it.
Second what I would suggest is to keep another key in your data class which sets value as per the viewHolderType it receives which would be something of as follows.
internal data class MessageListMetaDataItem(
#field:SerializedName("messageId")
val messageId: String = "",
#field:SerializedName("viewHolderType")
val viewHolderType: String = "",
#field:SerializedName("body")
val body: BaseMessageListItem = BaseMessageListItem()
) {
val viewHolderMapping: Int
get() = when(viewHolderType){
"textOnly" -> MessageListItemTypes.TEXT_ONLY
"textWithImage" -> MessageListItemTypes.TEXT_WITH_IMAGE
else -> MessageListItemTypes.UNKNOWN_TYPE
}
}
I am struggling to understand how to convert JSON data with Moshi. I am learning Android and Kotlin and my app is supposed to load and display COVID data. The input JSON format is like this:
[
{
"infected": 109782,
"tested": "NA",
"recovered": 75243,
"deceased": 2926,
"country": "Algeria",
"moreData": "https://api.apify.com/v2/key-value-stores/pp4Wo2slUJ78ZnaAi/records/LATEST?disableRedirect=true",
"historyData": "https://api.apify.com/v2/datasets/hi0DJXpcyzDwtg2Fm/items?format=json&clean=1",
"sourceUrl": "https://www.worldometers.info/coronavirus/",
"lastUpdatedApify": "2021-02-11T12:15:00.000Z"
},
{
"infected": 425561,
"tested": 11205451,
"recovered": 407155,
"deceased": 8138,
"country": "Austria",
"moreData": "https://api.apify.com/v2/key-value-stores/RJtyHLXtCepb4aYxB/records/LATEST?disableRedirect=true",
"historyData": "https://api.apify.com/v2/datasets/EFWZ2Q5JAtC6QDSwV/items?format=json&clean=1",
"sourceUrl": "https://www.sozialministerium.at/Informationen-zum-Coronavirus/Neuartiges-Coronavirus-(2019-nCov).html",
"lastUpdatedApify": "2021-02-11T12:15:00.000Z"
},
...
]
As you can see, numbers can also be represented as strings (as in 'tested'), also some URLs can be missing for some countries.
So I followed Moshi documentation and created 2 data classes and a custom adapter.
//desired structure
data class CountryData(
val infected: Int,
val tested: Int,
val recovered: Int,
val deceased: Int,
val country: String,
val moreData: String,
val historyData: String,
val sourceUrl: String,
val lastUpdatedApify: String
)
//actual JSON
data class CountryDataJson(
val infected: String,
val tested: String,
val recovered: String,
val deceased: String,
val country: String,
val moreData: String?,
val historyData: String?,
val sourceUrl: String?,
val lastUpdatedApify: String
)
Custom adapter:
import android.util.Log
import com.example.coronastats.network.CountryData
import com.example.coronastats.network.CountryDataJson
import com.squareup.moshi.FromJson
class CountryJsonAdapter {
#FromJson fun fromJson(countryDataJson: CountryDataJson): CountryData {
val countryData = CountryData(
if (countryDataJson.infected != "NA") countryDataJson.infected.toInt() else -1,
if (countryDataJson.tested != "NA") countryDataJson.tested.toInt() else -1,
if (countryDataJson.recovered != "NA") countryDataJson.recovered.toInt() else -1,
if (countryDataJson.deceased != "NA") countryDataJson.deceased.toInt() else -1,
countryDataJson.country,
countryDataJson.moreData ?: "NA",
countryDataJson.historyData ?: "NA",
countryDataJson.sourceUrl ?: "NA",
countryDataJson.lastUpdatedApify
)
Log.d("adapterLOG", "fromJson triggered")
return countryData
}
}
And my service API:
import com.example.coronastats.CountryJsonAdapter
import com.squareup.moshi.Moshi
import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
import retrofit2.Retrofit
import retrofit2.converter.moshi.MoshiConverterFactory
import retrofit2.http.GET
private const val BASE_URL = "https://api.apify.com/"
private val moshi = Moshi.Builder()
.add(CountryJsonAdapter())
.build()
private val retrofit = Retrofit.Builder()
.addConverterFactory(MoshiConverterFactory.create(moshi))
.baseUrl(BASE_URL)
.build()
interface CoronaApiService {
#GET("v2/key-value-stores/tVaYRsPHLjNdNBu7S/records/LATEST?disableRedirect=true")
suspend fun getStatistics() : List<CountryData>
}
object CoronaApi {
val retrofitService: CoronaApiService by lazy {
retrofit.create(CoronaApiService::class.java)
}
}
And I'm getting an empty screen as a result. The Log in the adapter is never triggered, so I assume something is wrong and my adapter is never called.
NB: Without all this converter stuff, the app runs ok with the standard KotlinJsonAdapterFactory() and CountryData class as all strings, but I'd like to know how to get the structure that I have here.
I believe that CountryDataJson is missing default values.
Reading the docs I've noticed the following:
In Kotlin, these fields must have a default value if they are in the primary constructor.
I have project with android app that fetch post from wordpress rest api
some field that i take is like this list.
[
{
"id": 43600,
"date": "2020-09-07T19:52:47",
"title": {
"rendered": "Video: .... "
},
"content": {
"rendered": "<div class=\"wp-block-embed__wrapper\"></div>",
"protected": false
},
"author": 31,
"featured_media": 43601,
"categories": [
788,
2760
]
}
]
Already read :
https://developer.android.com/training/data-storage/room
How to parse data of WordPress REST API using Retrofit and GSON?
Wordpress API - How to loop through a JSON Array of objects in Android/Java
Android Kotlin parsing nested JSON
Parse Json to Primative Array Kotlin
the closest answer but mostly in converter
Android Room Database: How to handle Arraylist in an Entity?
https://medium.com/#gilesjeremydev/room-through-a-complete-example-ce5c9ed417ba
I tried to save it into local storage with room in single entity. But based on google doc, it would seperate into 2 entities tied with annotation #relation
#Entity(tableName = "post")
data class SomePost(
#PrimaryKey
#field:SerializedName("id")
val id: Int,
#field:SerializedName("date")
val date: String,
#Embedded
#field:SerializedName("title")
val title: PostTitle,
#Embedded
#field:SerializedName("content")
val content: PostContent,
#field:SerializedName("featured_media")
val imageId: Int,
#field:SerializedName("author")
val author: Int
)
#Entity
data class PostCategories(
#PrimaryKey(autoGenerate = true)
val id: Int,
#field:SerializedName("categories")
val postCategories: Int
)
data class SomePostRelationship (
#Embedded
var post: SomePost? = null,
#Relation(
parentColumn = "id",
entityColumn = "categories"
)
var categories: List<PostCategories>? = null
)
interface PostService {
companion object {
const val ENDPOINT = "https://example.com/wp-json/"
}
// Posts
#GET("wp/v2/posts/")
suspend fun getPostAll(
#Query("page") page: Int? = null,
#Query("per_page") perPage: Int? = null,
#Query("search") search: String? = null,
#Query("order") order: String? = null
): Response<List<somePost>>
The problem is data class PostCategories.
My question is how to serialization json array into entity data class of categories for android room.
if there already answer or same question hope can link to it.
After tried some variation.
I decided to used converter and combine it in on dataclass for now.
#Entity(tableName = "post")
data class SomePost(
...
#field:SerializedName("categories")
var categories: ArrayList<Int>? = null,
...
)
class Converters {
...
#TypeConverter
fun listToInt(value: ArrayList<Int>?): String? {
return Gson().toJson(value)
}
#TypeConverter
fun intToList(value: String?): ArrayList<Int>? {
val type = object : TypeToken<ArrayList<Int>?>() {}.type
return Gson().fromJson(value, type)
}
}
I have a nested JSON like this from Server, as you can see there is a nested data in location
{
"id": "18941862",
"name": "Pizza Maru",
"url": "https://www.zomato.com/jakarta/pizza-maru-1-thamrin?utm_source=api_basic_user&utm_medium=api&utm_campaign=v2.1",
"location": {
"address": "Grand Indonesia Mall, East Mall, Lantai 3A, Jl. M.H. Thamrin No. 1, Thamrin, Jakarta",
"locality": "Grand Indonesia Mall, Thamrin",
"city": "Jakarta",
"city_id": 74,
"latitude": "-6.1954467635",
"longitude": "106.8216102943",
"zipcode": "",
"country_id": 94,
"locality_verbose": "Grand Indonesia Mall, Thamrin, Jakarta"
},
"currency": "IDR"
}
I am using retrofit and using gson converter. usually I need to make 2 data class for something like this to map JSON into POJO. so I need to make Restaurant class and also Location class, but I need to flatten that json object into single Restaurant class, like this
data class Restaurant : {
var id: String
var name: String
var url: String
var city: String
var latitude: Double
var longitude: Double
var zipcode: String
var currency: String
}
how to do that if I am using retrofit and gson converter ?
java or kotlin are ok
This solution is a silver bullet for this problem and cannot be appreciated enough.
Take this Kotlin file first:
/**
* credits to https://github.com/Tishka17/gson-flatten for inspiration
* Author: A$CE
*/
#Retention(AnnotationRetention.RUNTIME)
#Target(AnnotationTarget.FIELD)
annotation class Flatten(val path: String)
class FlattenTypeAdapterFactory(
private val pathDelimiter: String = "."
): TypeAdapterFactory {
override fun <T: Any?> create(gson: Gson, type: TypeToken<T>): TypeAdapter<T> {
val delegateAdapter = gson.getDelegateAdapter(this, type)
val defaultAdapter = gson.getAdapter(JsonElement::class.java)
val flattenedFieldsCache = buildFlattenedFieldsCache(type.rawType)
return object: TypeAdapter<T>() {
#Throws(IOException::class)
override fun read(reader: JsonReader): T {
// if this class has no flattened fields, parse it with regular adapter
if(flattenedFieldsCache.isEmpty())
return delegateAdapter.read(reader)
// read the whole json string into a jsonElement
val rootElement = defaultAdapter.read(reader)
// if not a json object (array, string, number, etc.), parse it
if(!rootElement.isJsonObject)
return delegateAdapter.fromJsonTree(rootElement)
// it's a json object of type T, let's deal with it
val root = rootElement.asJsonObject
// parse each field
for(field in flattenedFieldsCache) {
var element: JsonElement? = root
// dive down the path to find the right element
for(node in field.path) {
// can't dive down null elements, break
if(element == null) break
// reassign element to next node down
element = when {
element.isJsonObject -> element.asJsonObject[node]
element.isJsonArray -> try {
element.asJsonArray[node.toInt()]
} catch(e: Exception) { // NumberFormatException | IndexOutOfBoundsException
null
}
else -> null
}
}
// lift deep element to root element level
root.add(field.name, element)
// this keeps nested element un-removed (i suppose for speed)
}
// now parse flattened json
return delegateAdapter.fromJsonTree(root)
}
override fun write(out: JsonWriter, value: T) {
throw UnsupportedOperationException()
}
}.nullSafe()
}
// build a cache for flattened fields's paths and names (reflection happens only here)
private fun buildFlattenedFieldsCache(root: Class<*>): Array<FlattenedField> {
// get all flattened fields of this class
var clazz: Class<*>? = root
val flattenedFields = ArrayList<Field>()
while(clazz != null) {
clazz.declaredFields.filterTo(flattenedFields) {
it.isAnnotationPresent(Flatten::class.java)
}
clazz = clazz.superclass
}
if(flattenedFields.isEmpty()) {
return emptyArray()
}
val delimiter = pathDelimiter
return Array(flattenedFields.size) { i ->
val ff = flattenedFields[i]
val a = ff.getAnnotation(Flatten::class.java)!!
val nodes = a.path.split(delimiter)
.filterNot { it.isEmpty() } // ignore multiple or trailing dots
.toTypedArray()
FlattenedField(ff.name, nodes)
}
}
private class FlattenedField(val name: String, val path: Array<String>)
}
Then add it to Gson like this:
val gson = GsonBuilder()
.registerTypeAdapterFactory(FlattenTypeAdapterFactory())
.create()
Retrofit.Builder()
.baseUrl(baseUrl)
...
.addConverterFactory(GsonConverterFactory.create(gson))
.build()
Using your example, you can get the pojo parsed like this:
// prefer constructor properties
// prefer val over var
// prefer added #SerializedName annotation even to same-name properties:
// to future proof and for easier proguard rule config
data class Restaurant(
#SerializedName("id") val id: String,
#SerializedName("name") val name: String,
#SerializedName("url") val url: String,
#Flatten("location.city") val city: String,
#Flatten("location.latitude") val latitude: Double,
#Flatten("location.longitude") val longitude: Double,
#Flatten("location.zipcode") val zipcode: String,
#SerializedName("currency") var currency: String
)
You can even write a path down an array, e.g #Flatten("friends.0.name") = get first friend's name.
For more info, visit this repo
Note, however, that I stripped down the TypeAdapter to only read/consume json objects. You can implement write() if you want to use it to write json too.
You are welcome.
I am fairly new to Kotlin and I am trying to parse the JsonObject that I get from my HTTPRequest into data class. But I cannot get the Instance from the data class.
val jsonObjectRequest = JsonObjectRequest(Request.Method.GET, url, null,
Response.Listener { response ->
val text = "Response: %s".format(response.toString())
print(text)
},
Response.ErrorListener { error ->
// TODO: Handle error
}
)
#Throws(AuthFailureError::class)
#Override
fun getHeaders(): Map<String, String> {
var params = HashMap<String, String>()
if (params == null) params = HashMap()
val basicAuth = "Basic " + Base64.encodeToString("username:password".toByteArray(), Base64.NO_WRAP);
params["Authorization"] = basicAuth
//..add other headers
return params
}
TempJsonObject.instance?.addToRequestQueue(jsonObjectRequest)
Data Class
data class TempJsonObject(
val content: List<Content>) {
data class Content(
val kioskId: Int,
val location: Location,
val stats: Stats,
val settings: Settings,
val modules: String,
val visibility: String
) {
data class Stats(
val allLockers: Int,
val emptyLockers: Int,
val malfunctionLockers: Int,
val forCustomer: Int,
val forCourier: Int,
val bySize: BySize,
val incoming: Any
) {
data class BySize(
val XXSMALL: Xxsmall,
val XSMALL: Xsmall,
val SMALL: Small,
val MEDIUM: Medium,
val LARGE: Large,
val XLARGE: Xlarge
) {
data class Xxsmall(
val empty: Int,
val hasContent: Int
)
...
Is the way I am trying to do it the right approach and what am I doing wrong?
Looking at instance?.addToRequestQueue, it's really puzzling me. I don't know any Kotlin API like this for parsing JSONs. I thought that you use some library that adds such API, but you also wrote in the comment that the code doesn't compile because of lack of instance field. It looks like it exposes some singleton instance of the data class. Could you point me to any working example using such API, or any other source that you used?
If the above turns out to be incorrect, I would just use some Kotlin or Java library to parse the JSON into an instance of the data class. One option is the Kotlin library Klaxon: https://github.com/cbeust/klaxon. Quoting one of its examples that should fit your use case:
val result = Klaxon().parse<Person>(""" { "name": "John Smith", } """)
assert(result?.name == "John Smith")
assert(result.age == 23)