Kotlin1.3からWebAPIを呼び出す【Androidアプリ/Android Studio3.3 for MAC】

<uses-permission android:name="android.permission.INTERNET"/>

implementation 'com.squareup.okhttp3:okhttp:3.13.1'  //http通信ライブラリ
implementation 'com.eclipsesource.minimal-json:minimal-json:0.9.5' //jsonパースライブラリ
def coroutines_version = '1.0.1' //Kotlin coroutines用ライブラリ(async, await)のバージョン
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutines_version" //Kotlin coroutines用ライブラリ(async, await)
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutines_version" //Ko

    val getButton = findViewById(R.id.btn) as Button
    getButton.setOnClickListener(object : View.OnClickListener {
        override
        fun onClick(view: View) {
            onParallelGetButtonClick()
        }
    })

class HttpUtil {
    val HeaderKey = "H-API-KEY"
    val HeaderValue = "AUTH_API_KEY_20181203"

    //叩きたいREST APIのURLを引数とします
    fun httpGET1(url : String): String? {
        val client = OkHttpClient()
        val request = Request.Builder()
            .url(url)
            .addHeader(HeaderKey,HeaderValue)
            .build()

        val response = client.newCall(request).execute()
        return response.body()?.string()
    }
}

package com.example.myapplication

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.TextView
import com.eclipsesource.json.Json
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.async
import kotlinx.coroutines.launch
import okhttp3.OkHttpClient
import okhttp3.Request


private const val TAG = "MainActivity"


class MainActivity : AppCompatActivity() {
    val URL = "https://ssit.jp/api/holls" 
    var result = ""

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

        //android.os.Debug.waitForDebugger()

        val getButton = findViewById(R.id.btn) as Button
        getButton.setOnClickListener(object : View.OnClickListener {
            override
            fun onClick(view: View) {
                onParallelGetButtonClick()
            }
        })
    }

    //非同期処理でHTTP GETを実行します。
    fun onParallelGetButtonClick() = GlobalScope.launch(Dispatchers.Main) {
        val http = HttpUtil()

        val getText = findViewById(R.id.editText) as EditText
        val value = if(getText.text.toString() =="") "豊田市" else getText.text.toString()

        //Mainスレッドでネットワーク関連処理を実行するとエラーになるためBackgroundで実行
        async(Dispatchers.Default) { http.httpGET1("$URL/$value") }.await().let {
            //minimal-jsonを使って　jsonをパース
            val result = Json.parse(it).asObject()

            val cityName = findViewById(R.id.cityName) as TextView
            val zipCode = findViewById(R.id.zipCode) as TextView
            val hollAddress = findViewById(R.id.hollAddress) as TextView
            val tel = findViewById(R.id.tel) as TextView
            val zx = findViewById(R.id.zx) as TextView
            val zy = findViewById(R.id.zy) as TextView
            val tau = findViewById(R.id.tau) as TextView

            cityName.setText(result.get("cityName").asString())
            zipCode.setText(result.get("zipCode").asString())
            hollAddress.setText(result.get("hollAddress").asString())
            tel.setText(result.get("tel").asString())
            zx.setText(result.get("cx").toString())
            zy.setText(result.get("cy").toString())
            tau.setText(result.get("tau").toString())
        }
    }
}

class HttpUtil {
    val HeaderKey = "H-API-KEY"
    val HeaderValue = "AUTH_API_KEY_20181203"

    //叩きたいREST APIのURLを引数とします
    fun httpGET1(url : String): String? {
        val client = OkHttpClient()
        val request = Request.Builder()
            .url(url)
            .addHeader(HeaderKey,HeaderValue)
            .build()

        val response = client.newCall(request).execute()
        return response.body()?.string()
    }
}