An example client to Google Cloud Runtime Config, built in Kotlin with the Cloud Runtime Config API Java Lib

RuntimeConfigService.kt

package com.experiments.services

import com.google.api.client.googleapis.auth.oauth2.GoogleCredential
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport
import com.google.api.client.http.HttpRequestInitializer
import com.google.api.client.json.jackson2.JacksonFactory
import com.google.api.services.runtimeconfig.v1beta1.CloudRuntimeConfig
import com.google.api.services.runtimeconfig.v1beta1.CloudRuntimeConfigScopes
import com.google.api.services.runtimeconfig.v1beta1.model.Variable
import com.google.api.services.runtimeconfig.v1beta1.model.WatchVariableRequest
import lib.createLogger
import java.util.*


class RuntimeConfigService {

    private val log = createLogger()

    private val PROJECT = "YOUR-PROJECT-HERE" //Get your project code from the google cloud console
    private val CONFIG = "myConfigTest"
	private val SERVICE_ACCOUNT_JSON = "service-accounts/MY_SERVICE_ACCOUNT.json"
    private fun getVariablesPath(key: String)= "projects/$PROJECT/configs/$CONFIG/variables/$key"

    private val RUNTIME_CONFIG_CLIENT by lazy {
        val httpTransport = GoogleNetHttpTransport.newTrustedTransport()
        val jacksonFactory = JacksonFactory.getDefaultInstance()
        val googleCredential = authorize()
        CloudRuntimeConfig(httpTransport, jacksonFactory, setHttpTimeout(googleCredential))
    }

    fun create(key: String, value: String) {
        require(key.length < 256)

        val response = RUNTIME_CONFIG_CLIENT.projects().configs().variables()
            .create(getVariablesPath(key), Variable().setText(value)).execute()

        log.info("Created $key with value $value in GCP runtime config. Response: $response")
    }

    fun update(key: String, value: String) {
        require(key.length < 256)

        val response = RUNTIME_CONFIG_CLIENT.projects().configs().variables()
            .update(getVariablesPath(key), Variable().setText(value)).execute()

        log.info("Updated $key with value $value in GCP runtime config. Response: $response")
    }

    fun get(key: String): Variable? {
        require(key.length < 256)
        val response =
            RUNTIME_CONFIG_CLIENT.Projects().Configs().variables().get(getVariablesPath(key)).execute()
        log.info("Fetching $key with value $response from GCP runtime config")
        return response
    }

    fun delete(key: String) {
        require(key.length < 256)
        RUNTIME_CONFIG_CLIENT.Projects().Configs().variables().delete(getVariablesPath(key)).execute()
        log.info("Deleted $key from GCP runtime config")
    }

    fun watch(key: String): Variable? {
        require(key.length < 256)
        val response =
            RUNTIME_CONFIG_CLIENT.Projects().Configs().variables().watch(getVariablesPath(key), WatchVariableRequest()).execute()
        log.info("Fetching $key with value $response from GCP runtime config")
        return response
    }

    private fun authorize() =  GoogleCredential
        .fromStream(this::class.java.classLoader.getResource(SERVICE_ACCOUNT_JSON).openStream())
        .createScoped(Collections.singleton(CloudRuntimeConfigScopes.CLOUDRUNTIMECONFIG))


    private fun setHttpTimeout(requestInitializer: HttpRequestInitializer): HttpRequestInitializer {
        return HttpRequestInitializer {
            requestInitializer.initialize(it)
            it.connectTimeout = 3 * 60000
            it.readTimeout = 3 * 60000
        }
    }

}