You have secret key Base64 encoded, so you have first to decode it to plain byte array:
PHP:
$secret64 = "mtHa5YRivVrQ/ZNtoe2oxg==";
$secret = base64_decode($secret64);
$data = "11112222";
$hmac = hash_hmac('sha1', $data, $secret, true);
$hmac64 = base64_encode($signature);
echo $hmac64;
Java:
String data = "11112222";
String secret64 = "mtHa5YRivVrQ/ZNtoe2oxg==";
byte[] secret = Base64.decode(secret64, Base64.DEFAULT);
SecretKeySpec key = new SecretKeySpec(secret, "HmacSHA1");
Mac mac = Mac.getInstance("HmacSHA1");
mac.init(key);
byte[] bytes = mac.doFinal(data.getBytes("UTF-8"));
return Base64.encodeToString(bytes, Base64.DEFAULT);
Result:
LdKcsVyMX0BAhugGFEr4dAlFfe8=