그래픽 라이브러리 없이 Retrofit만 사용하여 이미지 출력

1. Gradle

implementation 'com.squareup.retrofit2:retrofit:2.5.0'
implementation 'com.squareup.retrofit2:converter-gson:2.5.0'

2. Permission

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

3. Interface(Retrofit)

interface RetrofitImageAPI {

    @GET("api/RetrofitAndroidImageResponse")
    fun getImageDetails(): Call<ResponseBody>

}

4. MainActivity.kt

class MainActivity : AppCompatActivity() {

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

        btnEvent()
    }


    //버튼클릭
    fun btnEvent(){

        btn_showimg.setOnClickListener {
            getRetrofitImage()
        }
    }


    internal fun getRetrofitImage() {

        val url = "http://www.androidtutorialpoint.com/"

        val retrofit = Retrofit.Builder()
                .baseUrl(url)
                .addConverterFactory(GsonConverterFactory.create())
                .build()

        val service = retrofit.create(RetrofitImageAPI::class.java)

        val call = service.getImageDetails()

        call.enqueue(object : Callback<ResponseBody> {
            override fun onResponse(call: Call<ResponseBody>, response: Response<ResponseBody>) {
                try {

                    Log.d("onResponse", "Response came from server")

                    val FileDownloaded = DownloadImage(response.body()!!)

                    Log.d("onResponse", "Image is downloaded and saved ? $FileDownloaded")

                } catch (e: Exception) {
                    Log.d("onResponse", "There is an error")
                    e.printStackTrace()
                }

            }


            override fun onFailure(call: Call<ResponseBody>, t: Throwable) {
                Log.d("onFailure", t.toString())
            }

        })
    }


    private fun DownloadImage(body: ResponseBody): Boolean {

        try {
            Log.d("DownloadImage", "Reading and writing file")
            var inputStream: InputStream? = null
            var outputStream: FileOutputStream? = null

            try {
                inputStream = body.byteStream()
                outputStream = FileOutputStream(getExternalFilesDir(null).toString() + File.separator + "AndroidTutorialPoint.jpg")
                var c: Int

                do{
                    c = inputStream.read()
                    outputStream.write(c)
                } while(c != -1)

            } catch (e: IOException) {
                Log.d("DownloadImage", e.toString())
                return false
            } finally {
                inputStream?.close()
                outputStream?.close()
            }

            val width: Int
            val height: Int
            val bMap = BitmapFactory.decodeFile(getExternalFilesDir(null).toString() + File.separator + "AndroidTutorialPoint.jpg")
            width = 2 * bMap.width
            height = 6 * bMap.height
            val bMap2 = Bitmap.createScaledBitmap(bMap, width, height, false)
            iv_test.setImageBitmap(bMap2)

            return true

        } catch (e: IOException) {
            Log.d("DownloadImage", e.toString())
            return false
        }

    }
}