android_apk_signature.java

private void getApkSignatureHash() {
    PackageManager packageManager = context.getPackageManager();
    String packageName = context.getPackageName();

    //Solution 1
    try {
        PackageInfo packageInfo = packageManager.getPackageInfo(packageName, PackageManager.GET_SIGNING_CERTIFICATES);
        //Deprecated packageInfo.signatures;
        Signature[] signatures = packageInfo.signatures;
        Signature signature = signatures[0];
        String sign = signature.toCharsString();
        String hash = md5(sign);
    } catch (PackageManager.NameNotFoundException e) {
        e.printStackTrace();
    }

    /*
    Solution 2
    try {
        PackageInfo packageInfo = packageManager.getPackageInfo(packageName, PackageManager.GET_SIGNING_CERTIFICATES);
        SigningInfo signingInfo = packageInfo.signingInfo;
        Signature[] signatures = signingInfo.getApkContentsSigners();
        Signature signature = signatures[0];
        String sign = signature.toCharsString();
        String hash = md5(sign);
    } catch (PackageManager.NameNotFoundException e) {
        e.printStackTrace();
    }
     */
}

android_apk_signature.kt

fun getApkSignatureHash() {
    val packageManager = context.packageManager
    val packageName = context.packageName

    //Solution 1
    try {
        val packageInfo = packageManager.getPackageInfo(packageName, PackageManager.GET_SIGNING_CERTIFICATES)
        //Deprecated packageInfo.signatures;
        val signatures = packageInfo.signatures
        val signature = signatures[0]
        val sign = signature.toCharsString()
        val hash: String = md5(sign)
    } catch (e: PackageManager.NameNotFoundException) {
        e.printStackTrace()
    }

    /*
    //Solution 2
    try {
        val packageInfo = packageManager.getPackageInfo(packageName, PackageManager.GET_SIGNING_CERTIFICATES)
        val signingInfo = packageInfo.signingInfo
        val signatures = signingInfo.getApkContentsSigners()
        val signature = signatures[0]
        val sign = signature.toCharsString()
        val hash = md5(sign)
    } catch (e: PackageManager.NameNotFoundException) {
        e.printStackTrace();
    }
   */
}

md5 function from @dlimpid : https://gist.github.com/dlimpid/68761108b49b7c1ddb84250dfac78495