private void checkInitialization() {
		if (sslContext == null) {
			throw new IllegalStateException(
					"SSL Certificates and attribute are not initialized\n"
							+ "Use .withCert() methods.");
		}

		if (executor == null) {
			throw new IllegalStateException(
					"SSL Certificates and attribute are not initialized\n"
							+ "Use .withCert() methods.");
		}

		if (gatewayPort == -1 || feedbackPort == -1) {
			throw new IllegalStateException(
					"The Destination APNS server is not stated\n"
							+ "Use .withDestination(), withSandboxDestination(), "
							+ "or withProductionDestination().");
		}
	}
Returns a fully initialized instance of {@link ApnsService}, according to
the requested settings.

@return a new instance of ApnsService
@throws IOException
src/test/java/com/notnoop/apns/ApnsServerSocketBuilder.java