spring-messaging-demo/rabbitmq/src/main/java/com/ankurm/rabbit/Topology.java

package com.ankurm.rabbit;

import org.springframework.amqp.core.Binding;
import org.springframework.amqp.core.BindingBuilder;
import org.springframework.amqp.core.DirectExchange;
import org.springframework.amqp.core.FanoutExchange;
import org.springframework.amqp.core.HeadersExchange;
import org.springframework.amqp.core.Queue;
import org.springframework.amqp.core.QueueBuilder;
import org.springframework.amqp.core.TopicExchange;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.Map;

/**
 * The whole topology as beans. {@code RabbitAdmin} declares every {@code Exchange},
 * {@code Queue} and {@code Binding} bean when the connection is first opened.
 *
 * <p>Two things about that are worth knowing before you rely on it:
 * <ul>
 *   <li>Declaration is <b>idempotent only if the arguments match</b>. Redeclaring an existing
 *       queue with different arguments is a channel-level {@code PRECONDITION_FAILED} &mdash; see
 *       docs/06-changing-your-mind.md.</li>
 *   <li>Declarations happen on connection, not on context refresh, so a topology error surfaces
 *       at the first publish rather than at startup.</li>
 * </ul>
 *
 * @see <a href="../../../../../docs/02-exchanges.md">docs/02-exchanges.md</a>
 */
@Configuration(proxyBeanMethods = false)
public class Topology {

	public static final String DIRECT = "orders.direct";

	public static final String FANOUT = "orders.fanout";

	public static final String TOPIC = "orders.topic";

	public static final String HEADERS = "orders.headers";

	public static final String DLX = "orders.dlx";

	public static final String Q_NEW = "orders.new";

	public static final String Q_CANCEL = "orders.cancel";

	public static final String Q_AUDIT = "audit.all";

	public static final String Q_ANALYTICS = "analytics.all";

	public static final String Q_EU = "orders.eu";

	public static final String Q_HIGH = "orders.high";

	public static final String Q_PRIORITY = "orders.priority";

	public static final String Q_ANY = "orders.any";

	public static final String Q_WORK = "orders.work";

	public static final String Q_TTL = "orders.ttl";

	public static final String Q_DLQ = "orders.dlq";

	// --- direct: routing key must match the binding key exactly -----------------------------

	@Bean
	DirectExchange directExchange() {
		return new DirectExchange(DIRECT);
	}

	@Bean
	Queue newQueue() {
		return QueueBuilder.durable(Q_NEW).build();
	}

	@Bean
	Queue cancelQueue() {
		return QueueBuilder.durable(Q_CANCEL).build();
	}

	@Bean
	Binding bindNew(DirectExchange directExchange, Queue newQueue) {
		return BindingBuilder.bind(newQueue).to(directExchange).with("new");
	}

	@Bean
	Binding bindCancel(DirectExchange directExchange, Queue cancelQueue) {
		return BindingBuilder.bind(cancelQueue).to(directExchange).with("cancel");
	}

	// --- fanout: routing key ignored entirely -----------------------------------------------

	@Bean
	FanoutExchange fanoutExchange() {
		return new FanoutExchange(FANOUT);
	}

	@Bean
	Queue auditQueue() {
		return QueueBuilder.durable(Q_AUDIT).build();
	}

	@Bean
	Queue analyticsQueue() {
		return QueueBuilder.durable(Q_ANALYTICS).build();
	}

	@Bean
	Binding bindAudit(FanoutExchange fanoutExchange, Queue auditQueue) {
		return BindingBuilder.bind(auditQueue).to(fanoutExchange);
	}

	@Bean
	Binding bindAnalytics(FanoutExchange fanoutExchange, Queue analyticsQueue) {
		return BindingBuilder.bind(analyticsQueue).to(fanoutExchange);
	}

	// --- topic: '*' is exactly one word, '#' is zero or more -------------------------------

	@Bean
	TopicExchange topicExchange() {
		return new TopicExchange(TOPIC);
	}

	@Bean
	Queue euQueue() {
		return QueueBuilder.durable(Q_EU).build();
	}

	@Bean
	Queue highQueue() {
		return QueueBuilder.durable(Q_HIGH).build();
	}

	@Bean
	Binding bindEu(TopicExchange topicExchange, Queue euQueue) {
		return BindingBuilder.bind(euQueue).to(topicExchange).with("order.eu.*");
	}

	@Bean
	Binding bindHigh(TopicExchange topicExchange, Queue highQueue) {
		return BindingBuilder.bind(highQueue).to(topicExchange).with("order.#.high");
	}

	// --- headers: routing key ignored, header map matched ------------------------------------

	@Bean
	HeadersExchange headersExchange() {
		return new HeadersExchange(HEADERS);
	}

	@Bean
	Queue priorityQueue() {
		return QueueBuilder.durable(Q_PRIORITY).build();
	}

	@Bean
	Queue anyQueue() {
		return QueueBuilder.durable(Q_ANY).build();
	}

	/** x-match=all: every header must match. */
	@Bean
	Binding bindPriority(HeadersExchange headersExchange, Queue priorityQueue) {
		return BindingBuilder.bind(priorityQueue).to(headersExchange)
				.whereAll(Map.of("priority", "high", "region", "eu")).match();
	}

	/** x-match=any: one is enough. */
	@Bean
	Binding bindAny(HeadersExchange headersExchange, Queue anyQueue) {
		return BindingBuilder.bind(anyQueue).to(headersExchange)
				.whereAny(Map.of("priority", "high", "region", "eu")).match();
	}

	// --- the dead-letter path ----------------------------------------------------------------

	@Bean
	DirectExchange deadLetterExchange() {
		return new DirectExchange(DLX);
	}

	@Bean
	Queue deadLetterQueue() {
		// Deliberately NO dead-letter-exchange on the DLQ itself. Pointing a DLQ's DLX back at
		// the exchange that feeds it is the classic infinite loop.
		return QueueBuilder.durable(Q_DLQ).build();
	}

	@Bean
	Binding bindDlq(DirectExchange deadLetterExchange, Queue deadLetterQueue) {
		// The routing key used when dead-lettering is the message's ORIGINAL routing key unless
		// deadLetterRoutingKey() overrides it. Both work queues below set it explicitly to
		// "failed", so this one binding catches everything.
		return BindingBuilder.bind(deadLetterQueue).to(deadLetterExchange).with("failed");
	}

	@Bean
	Queue workQueue() {
		return QueueBuilder.durable(Q_WORK)
				.deadLetterExchange(DLX)
				.deadLetterRoutingKey("failed")
				.build();
	}

	@Bean
	Queue ttlQueue() {
		return QueueBuilder.durable(Q_TTL)
				.ttl(1500)
				.deadLetterExchange(DLX)
				.deadLetterRoutingKey("failed")
				.build();
	}

}