@Override
	protected Class<?>[] supportedPayloadTypes() {
		return new Class<?>[] { String.class };
	}
A {@link org.springframework.messaging.converter.MessageConverter}
to convert a String to a byte[], applying the provided Charset in
the content-type header if any.

@author David Turanski
spring-xd-dirt/src/main/java/org/springframework/xd/dirt/integration/bus/converter/StringToByteArrayMessageConverter.java