Adds spring-cloud-starter-bootstrap.

This allows users to opt-in to bootstrap via classpath rather than properties.

pom.xml

@@ -161,6 +161,7 @@
 		<module>spring-cloud-commons</module>
 		<module>spring-cloud-loadbalancer</module>
 		<module>spring-cloud-starter</module>
+		<module>spring-cloud-starter-bootstrap</module>
 		<module>spring-cloud-starter-loadbalancer</module>
 		<module>docs</module>
 	</modules>

spring-cloud-commons-dependencies/pom.xml

@@ -54,6 +54,11 @@
 				<artifactId>spring-cloud-starter</artifactId>
 				<version>${project.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.springframework.cloud</groupId>
+				<artifactId>spring-cloud-starter-bootstrap</artifactId>
+				<version>${project.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.springframework.cloud</groupId>
 				<artifactId>spring-cloud-starter-loadbalancer</artifactId>

spring-cloud-context/src/main/java/org/springframework/cloud/util/ConditionalOnBootstrapDisabled.java

@@ -22,6 +22,7 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.condition.NoneNestedConditions;
 import org.springframework.context.annotation.Conditional;
@@ -41,6 +42,11 @@ public @interface ConditionalOnBootstrapDisabled {
 			super(ConfigurationPhase.REGISTER_BEAN);
 		}
 
+		@ConditionalOnClass(name = "org.springframework.cloud.bootstrap.marker.Marker")
+		static class OnBootstrapMarkerClassPresent {
+
+		}
+
 		@ConditionalOnProperty(name = USE_LEGACY_PROCESSING_PROPERTY)
 		static class OnUseLegacyProcessingEnabled {
 

spring-cloud-context/src/main/java/org/springframework/cloud/util/ConditionalOnBootstrapEnabled.java

@@ -23,6 +23,7 @@ import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
 import org.springframework.boot.autoconfigure.condition.AnyNestedCondition;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Conditional;
 
@@ -41,6 +42,11 @@ public @interface ConditionalOnBootstrapEnabled {
 			super(ConfigurationPhase.REGISTER_BEAN);
 		}
 
+		@ConditionalOnClass(name = PropertyUtils.MARKER_CLASS)
+		static class OnBootstrapMarkerClassPresent {
+
+		}
+
 		@ConditionalOnProperty(name = USE_LEGACY_PROCESSING_PROPERTY)
 		static class OnUseLegacyProcessingEnabled {
 

spring-cloud-context/src/main/java/org/springframework/cloud/util/PropertyUtils.java

@@ -17,6 +17,7 @@
 package org.springframework.cloud.util;
 
 import org.springframework.core.env.Environment;
+import org.springframework.util.ClassUtils;
 
 public abstract class PropertyUtils {
 
@@ -30,12 +31,33 @@ public abstract class PropertyUtils {
 	 */
 	public static final String USE_LEGACY_PROCESSING_PROPERTY = "spring.config.use-legacy-processing";
 
+	/**
+	 * Property name for bootstrap marker class name.
+	 */
+	public static final String MARKER_CLASS = "org.springframework.cloud.bootstrap.marker.Marker";
+
+	/**
+	 * Boolean if bootstrap marker class exists.
+	 */
+	public static final boolean MARKER_CLASS_EXISTS = markerClassExists();
+
+	private static boolean markerClassExists() {
+		try {
+			ClassUtils.forName(MARKER_CLASS, null);
+			return true;
+		}
+		catch (ClassNotFoundException e) {
+			return false;
+		}
+	}
+
 	private PropertyUtils() {
 
 	}
 
 	public static boolean bootstrapEnabled(Environment environment) {
-		return environment.getProperty(BOOTSTRAP_ENABLED_PROPERTY, Boolean.class, false);
+		return environment.getProperty(BOOTSTRAP_ENABLED_PROPERTY, Boolean.class, false)
+				|| MARKER_CLASS_EXISTS;
 	}
 
 	public static boolean useLegacyProcessing(Environment environment) {

spring-cloud-starter-bootstrap/pom.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+		 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<parent>
+		<groupId>org.springframework.cloud</groupId>
+		<artifactId>spring-cloud-commons-parent</artifactId>
+		<version>3.0.0-SNAPSHOT</version>
+		<relativePath>..</relativePath>
+	</parent>
+	<packaging>jar</packaging>
+	<modelVersion>4.0.0</modelVersion>
+	<artifactId>spring-cloud-starter-bootstrap</artifactId>
+	<name>spring-cloud-starter-bootstrap</name>
+	<description>Spring Cloud Starter Bootstrap</description>
+	<url>https://projects.spring.io/spring-cloud</url>
+	<organization>
+		<name>Pivotal Software, Inc.</name>
+		<url>https://www.spring.io</url>
+	</organization>
+	<properties>
+		<main.basedir>${basedir}/../..</main.basedir>
+	</properties>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.cloud</groupId>
+			<artifactId>spring-cloud-starter</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+</project>

spring-cloud-starter-bootstrap/src/main/java/org/springframework/cloud/bootstrap/marker/Marker.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2013-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.bootstrap.marker;
+
+/**
+ * A marker class, so that, if present, spring cloud bootstrap is enable similar to how
+ * 'spring.cloud.bootstrap.enabled=true' works.
+ */
+public abstract class Marker {
+
+	private Marker() {
+
+	}
+
+}

spring-cloud-starter-bootstrap/src/test/java/org/springframework/cloud/bootstrap/marker/MarkerTests.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2013-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.bootstrap.marker;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.core.env.Environment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@SpringBootTest
+public class MarkerTests {
+
+	@Autowired
+	private Environment env;
+
+	@Test
+	public void testBootstrapIsEnabled() {
+		assertThat(env.getProperty("my.prop")).isEqualTo("my.value");
+	}
+
+	@SpringBootConfiguration
+	@EnableAutoConfiguration
+	protected static class TestConfig {
+
+	}
+}

spring-cloud-starter-bootstrap/src/test/resources/bootstrap.properties

@@ -0,0 +1 @@
+my.prop=my.value