private boolean isLegalChannelPrefix(String string) {
		return string.equals(ChannelPrefix.queue.toString()) ||
				string.equals(ChannelPrefix.topic.toString()) ||
				string.equals(ChannelPrefix.tap.toString());
	}
Parse a stream definition.

@return the AST for the parsed stream
@throws StreamDefinitionException
spring-xd-dirt/src/main/java/org/springframework/xd/dirt/stream/dsl/StreamConfigParser.java