Reinstate auto-configuration support for embedded ActiveMQ

This commit restores auto-configuration for using an Embedded broker
with ActiveMQ classic.

Contrary to its 2.7.x version, "spring-boot-starter-activemq" no longer
adds the broker for consistency with Artemis, and to keep the existing
3.x behavior. Rather than "inMemory", a "s.a.embedded.enabled"
property has been reintroduced that matches the name used by Artemis.

The documentation has been updated to mention that the broker
dependency must be added to use it.

Closes gh-38404

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,6 +37,8 @@ import org.springframework.boot.context.properties.NestedConfigurationProperty;
 @ConfigurationProperties(prefix = "spring.activemq")
 public class ActiveMQProperties {
 
+	private static final String DEFAULT_EMBEDDED_BROKER_URL = "vm://localhost?broker.persistent=false";
+
 	private static final String DEFAULT_NETWORK_BROKER_URL = "tcp://localhost:61616";
 
 	/**
@@ -54,6 +56,8 @@ public class ActiveMQProperties {
 	 */
 	private String password;
 
+	private final Embedded embedded = new Embedded();
+
 	/**
 	 * Time to wait before considering a close complete.
 	 */
@@ -99,6 +103,10 @@ public class ActiveMQProperties {
 		this.password = password;
 	}
 
+	public Embedded getEmbedded() {
+		return this.embedded;
+	}
+
 	public Duration getCloseTimeout() {
 		return this.closeTimeout;
 	}
@@ -135,9 +143,32 @@ public class ActiveMQProperties {
 		if (this.brokerUrl != null) {
 			return this.brokerUrl;
 		}
+		if (this.embedded.isEnabled()) {
+			return DEFAULT_EMBEDDED_BROKER_URL;
+		}
 		return DEFAULT_NETWORK_BROKER_URL;
 	}
 
+	/**
+	 * Configuration for an embedded ActiveMQ broker.
+	 */
+	public static class Embedded {
+
+		/**
+		 * Whether to enable embedded mode if the ActiveMQ Broker is available.
+		 */
+		private boolean enabled = true;
+
+		public boolean isEnabled() {
+			return this.enabled;
+		}
+
+		public void setEnabled(boolean enabled) {
+			this.enabled = enabled;
+		}
+
+	}
+
 	public static class Packages {
 
 		/**

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,14 +48,14 @@ class ActiveMQAutoConfigurationTests {
 		.withConfiguration(AutoConfigurations.of(ActiveMQAutoConfiguration.class, JmsAutoConfiguration.class));
 
 	@Test
-	void brokerIsLocalhostByDefault() {
+	void brokerIsEmbeddedByDefault() {
 		this.contextRunner.withUserConfiguration(EmptyConfiguration.class).run((context) -> {
 			assertThat(context).hasSingleBean(CachingConnectionFactory.class).hasBean("jmsConnectionFactory");
 			CachingConnectionFactory connectionFactory = context.getBean(CachingConnectionFactory.class);
 			assertThat(context.getBean("jmsConnectionFactory")).isSameAs(connectionFactory);
 			assertThat(connectionFactory.getTargetConnectionFactory()).isInstanceOf(ActiveMQConnectionFactory.class);
 			assertThat(((ActiveMQConnectionFactory) connectionFactory.getTargetConnectionFactory()).getBrokerURL())
-				.isEqualTo("tcp://localhost:61616");
+				.isEqualTo("vm://localhost?broker.persistent=false");
 		});
 	}
 

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQPropertiesTests.java

@@ -31,13 +31,15 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 class ActiveMQPropertiesTests {
 
+	private static final String DEFAULT_EMBEDDED_BROKER_URL = "vm://localhost?broker.persistent=false";
+
 	private static final String DEFAULT_NETWORK_BROKER_URL = "tcp://localhost:61616";
 
 	private final ActiveMQProperties properties = new ActiveMQProperties();
 
 	@Test
-	void getBrokerUrlIsLocalhostByDefault() {
-		assertThat(this.properties.determineBrokerUrl()).isEqualTo(DEFAULT_NETWORK_BROKER_URL);
+	void getBrokerUrlIsEmbeddedByDefault() {
+		assertThat(this.properties.determineBrokerUrl()).isEqualTo(DEFAULT_EMBEDDED_BROKER_URL);
 	}
 
 	@Test
@@ -46,6 +48,19 @@ class ActiveMQPropertiesTests {
 		assertThat(this.properties.determineBrokerUrl()).isEqualTo("tcp://activemq.example.com:71717");
 	}
 
+	@Test
+	void getBrokerUrlWithEmbeddedSetToFalse() {
+		this.properties.getEmbedded().setEnabled(false);
+		assertThat(this.properties.determineBrokerUrl()).isEqualTo(DEFAULT_NETWORK_BROKER_URL);
+	}
+
+	@Test
+	void getExplicitBrokerUrlAlwaysWins() {
+		this.properties.setBrokerUrl("tcp://activemq.example.com:71717");
+		this.properties.getEmbedded().setEnabled(false);
+		assertThat(this.properties.determineBrokerUrl()).isEqualTo("tcp://activemq.example.com:71717");
+	}
+
 	@Test
 	void setTrustAllPackages() {
 		ActiveMQConnectionFactory factory = new ActiveMQConnectionFactory();