java-design-patterns/poison-pill/src/main/java/com/iluwatar/Message.java

package com.iluwatar;

import java.util.Map;

/**
 * Interface that implements the Message pattern and represents an inbound or outbound message as part of an {@link Producer}-{@link Consumer} exchange.
 */
public interface Message {

	public static final Message POISON_PILL = new Message() {

		@Override
		public void addHeader(Headers header, String value) {
			throw poison();
		}

		@Override
		public String getHeader(Headers header) {
			throw poison();
		}

		@Override
		public Map<Headers, String> getHeaders() {
			throw poison();
		}

		@Override
		public void setBody(String body) {
			throw poison();
		}

		@Override
		public String getBody() {
			throw poison();
		}

		private RuntimeException poison() {
			return new UnsupportedOperationException("Poison");
		}

	};

	public enum Headers {
		DATE, SENDER
	}

	public void addHeader(Headers header, String value);
	public String getHeader(Headers header);
	public Map<Headers, String> getHeaders();
	public void setBody(String body);
	public String getBody();
}