Moshi (converting json text to a class object) | deserialization in Kotlin

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Moshi (converting json text to a class object) | deserialization in Kotlin | Android Studio

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Moshi (converting json text to a class object) | deserialization in Kotlin | Android Studio

last updated: 30 November 2023

Converts any json text. For example:

{ "Name": "Super good", "Price": 7 }

And creates any type of object. For example:

var book: MyBook? = ConvertJsonToObject(moshi, jsonText)

Note!
The ConvertJsonToObject function does not need to be changed, it is template or generic.
In order to convert json text to another class object, you need to:

val moshi:Moshi = Moshi.Builder().build()

val jsonText1 = """
{ "Name": "Super good", "Price": 7 }
"""
var book: MyBook? = ConvertJsonToObject(moshi, jsonText1)

val jsonText2 = """
{ "Location": "Street sunny", "Time": "12:43:15 PM" }
"""
var film: MyFilm? = ConvertJsonToObject(moshi, jsonText2)

Step 1. Creating a new project

Create a new simple project "Empty Views Activity" on Kotlin in Android Studio ...

Step 2. Let's change the code in the file MainActivity.kt

My added code is filled in:

Kotlin File MainActivity.kt

package com.example.androidkotlinapp1

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.squareup.moshi.JsonAdapter
import com.squareup.moshi.JsonClass
import com.squareup.moshi.Moshi

@JsonClass(generateAdapter = true)
data class MyBook(
     val Name: String = "",
     val Price: Int = 0
)

inline fun <reified T> ConvertJsonToObject(moshi:Moshi, jsonText:String): T?
{
     val moshiAdapter: JsonAdapter<T> = moshi.adapter(T::class.java)
     return moshiAdapter.fromJson(jsonText)
}

class MainActivity : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          setContentView(R.layout.activity_main)

          // my functionality
          val moshi:Moshi = Moshi.Builder().build()

          try {
               val jsonText = """
                    { "Name": "Super good", "Price": 7, "Description": "123" }
               """

               var book: MyBook? = ConvertJsonToObject(moshi, jsonText)

               println("Book: ${book!!.Name.toString()} , ${book!!.Price.toString()}")
          }
          catch (e:Exception)
          {
               println("Exception: ${e.message}")
          }
     }
}

Explanation:

Here is my class MyBook:

@JsonClass(generateAdapter = true)
data class MyBook(
val Name: String = "",
val Price: Int = 0
)

Description:
The @JsonClass attribute is needed for JSON conversion.

Since the class will only contain data without methods, I'll use the word data.
The word data means that the compiler for the class will add new members from the parameters in the constructor.

My ConvertJsonToObject function converts the json text to an object of type T and returns that object:

inline fun <reified T> ConvertJsonToObject(moshi:Moshi, jsonText:String): T?
{
val moshiAdapter: JsonAdapter<T> = moshi.adapter(T::class.java)
return moshiAdapter.fromJson(jsonText)
}

Description:
My function ConvertJsonToObject returns an unknown type T?.

At the beginning of the function, I specified inline <reified T>, which means that the function is template or generic, i.e. it will use an unknown type T.

Or you can do it like this:

~~inline~~ fun ~~<reified T>~~ <T> ConvertJsonToObject(moshi:Moshi, jsonText:String): T?

At the beginning of the function, I could specify <T>, which means that the function is also template or generic, i.e. it will use an unknown type T.

Why I'm using: inline <reified T>
Answer: That's the only way I can use T::class.java

val jsonText = """
{ "Name": "Super good", "Price": 7, "Description": "123" }
"""

The jsonText variable contains text in the format json.

Note! I'm using """ to use the " character inside the text.

Step 3. Let's change the code in the file build.gradle

My added code is filled in:

File build.gradle

plugins {
     id 'com.android.application'
     id 'org.jetbrains.kotlin.android'
}

apply plugin: 'kotlin-kapt'

android {
     namespace 'com.example.androidkotlinapp1'
     compileSdk 33

     defaultConfig {
          applicationId "com.example.androidkotlinapp1"
          minSdk 27
          targetSdk 33
          versionCode 1
          versionName "1.0"

          testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }

     buildTypes {
          release {
               minifyEnabled false
               proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
          }
     }
     compileOptions {
          sourceCompatibility JavaVersion.VERSION_1_8
          targetCompatibility JavaVersion.VERSION_1_8
     }
     kotlinOptions {
          jvmTarget = '1.8'
     }
}

dependencies {
     implementation 'androidx.core:core-ktx:1.7.0'
     implementation 'androidx.appcompat:appcompat:1.6.1'
     implementation 'com.google.android.material:material:1.9.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
     testImplementation 'junit:junit:4.13.2'
     androidTestImplementation 'androidx.test.ext:junit:1.1.5'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'

     // Moshi deserialization
     implementation 'com.squareup.moshi:moshi:1.14.0'
     kapt 'com.squareup.moshi:moshi-kotlin-codegen:1.14.0'
}

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