ShowImageSameUrl.kt

package com.miller.futurechat

import android.content.Context
import android.util.Log
import android.widget.ImageView
import com.bumptech.glide.Glide
import com.bumptech.glide.signature.ObjectKey
import io.reactivex.Single
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.schedulers.Schedulers
import okhttp3.OkHttpClient
import retrofit2.Response
import retrofit2.Retrofit
import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory
import retrofit2.http.HEAD

/**
 * Created by Miller on 17/09/2019
 */

interface ApiService {

    @HEAD("http://lorempixel.com/400/200/")
    fun getImageDate(): Single<Response<Void>>
}

// Put in other class

fun showGlideImage(context: Context, target: ImageView) {
    val client = OkHttpClient()
    val retrofit = Retrofit.Builder()
        .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
        .client(client)
        .baseUrl("http://mock.api")
        .build()
    val apiService = retrofit.create(ApiService::class.java)
    apiService.getImageDate()
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(
            {
                val date = it.headers()["date"]
                Log.d("----->","MainActivity - onResponse : $date")
                Glide.with(context)
                    .load("http://lorempixel.com/400/200/")
                    .signature(ObjectKey(date ?: ""))
                    .into(target)
            },
            {
                it.printStackTrace()
            }
        )
        .apply {
            CompositeDisposable().add(this)
        }
}

Response header from http://lorempixel.com/400/200/ doesn't have Etag and Content-Length, so I have to use date instead for demo purpose