Kotlin - convert UTC to local time

I'm trying to convert a UTC string date to local time, so it's in a more readable format. I have a textView that in my activity layout:

<TextView
    android:id="@+id/dateTv"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="8dp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/titleTv"
    tools:text="Published Date" />

In my activity:

class FullArticleActivity : AppCompatActivity() {

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

    val articleJson = intent.getStringExtra(ARTICLE_KEY)


    if(!articleJson.isNullOrBlank()) {
      val article = Gson().fromJson<Article>(articleJson, Article::class.java)

        val formatter = SimpleDateFormat("yyyy-MM-dd HH:mm:ssZ", Locale.getDefault())
        formatter.timeZone = TimeZone.getTimeZone("UTC")
        val formattedDate = formatter.parse(article.publishedAt)

      titleTv.text = article.title
      //UTC string
      dateTv.text = article.publishedAt
      contentTv.text = article.content

The publishedAt string is in this format from the api call "2018-12-10T19:48:39Z". How can I convert this ZULU time format to local time?

Solution

Try using Extension Functions

fun String.toDate(
    dateFormat: String = "yyyy-MM-dd HH:mm:ss",
    timeZone: TimeZone = TimeZone.getTimeZone("UTC"),
): Date {
    val parser = SimpleDateFormat(dateFormat, Locale.getDefault())
    parser.timeZone = timeZone
    return parser.parse(this)
}

fun Date.formatTo(
    dateFormat: String,
    timeZone: TimeZone = TimeZone.getDefault(),
): String {
    val formatter = SimpleDateFormat(
        dateFormat, Locale.getDefault()
    )
    formatter.timeZone = timeZone
    return formatter.format(this)
}

Usage:

"2018-09-10 22:01:00".toDate().formatTo("dd MMM yyyy")

Output: "11 Sep 2018"