Ensure there is a single bootstrap parent context

Only one neds to be created, and once it is in place in the hierarchy
it should be usable by all the child contexts that get added.

Fixes gh-153

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/TestHigherPriorityBootstrapConfiguration.java

@@ -1,5 +1,6 @@
 package org.springframework.cloud.bootstrap;
 
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.springframework.core.Ordered;
@@ -12,8 +13,11 @@ import org.springframework.core.annotation.Order;
 public class TestHigherPriorityBootstrapConfiguration {
 
 	static final AtomicReference<Class<?>> firstToBeCreated = new AtomicReference<>();
+	
+	public static final AtomicInteger count = new AtomicInteger();
 
 	public TestHigherPriorityBootstrapConfiguration() {
+		count.incrementAndGet();
 		firstToBeCreated.compareAndSet(null, TestHigherPriorityBootstrapConfiguration.class);
 	}
 

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/config/BootstrapConfigurationTests.java

@@ -28,6 +28,7 @@ import org.junit.rules.ExpectedException;
 import org.springframework.boot.builder.SpringApplicationBuilder;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.cloud.bootstrap.TestHigherPriorityBootstrapConfiguration;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Configuration;
@@ -42,6 +43,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
 /**
@@ -270,6 +272,18 @@ public class BootstrapConfigurationTests {
 		assertEquals(0, sources.precedenceOf(bootstrap));
 	}
 
+	@Test
+	public void onlyOneBootstrapContext() {
+		TestHigherPriorityBootstrapConfiguration.count.set(0);
+		PropertySourceConfiguration.MAP.put("bootstrap.foo", "bar");
+		this.context = new SpringApplicationBuilder().sources(BareConfiguration.class)
+				.child(BareConfiguration.class).web(false).run();
+		assertEquals(1, TestHigherPriorityBootstrapConfiguration.count.get());
+		assertNotNull(context.getParent());
+		assertEquals("bootstrap", context.getParent().getParent().getId());
+		assertNull(context.getParent().getParent().getParent());
+	}
+
 	@Test
 	public void environmentEnrichedInParentContext() {
 		PropertySourceConfiguration.MAP.put("bootstrap.foo", "bar");

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/config/BootstrapListenerHierarchyIntegrationTests.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2013-2017 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
+ *
+ *      http://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.config;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import org.junit.Test;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Integration tests for Bootstrap Listener's functionality of adding a bootstrap context
+ * as the root Application Context
+ * 
+ * @author Biju Kunjummen
+ */
+public class BootstrapListenerHierarchyIntegrationTests {
+
+	@Test
+	public void shouldAddInABootstrapContext() {
+		ConfigurableApplicationContext context = new SpringApplicationBuilder()
+				.sources(BasicConfiguration.class).web(false).run();
+
+		assertNotNull(context.getParent());
+	}
+
+	@Test
+	public void shouldAddInOneBootstrapForABasicParentChildHierarchy() {
+		ConfigurableApplicationContext context = new SpringApplicationBuilder()
+				.sources(RootConfiguration.class).web(false)
+				.child(BasicConfiguration.class).web(false).run();
+
+		// Should be RootConfiguration based context
+		ConfigurableApplicationContext parent = (ConfigurableApplicationContext) context
+				.getParent();
+		assertEquals("rootBean", parent.getBean("rootBean", String.class));
+
+		// Parent should have the bootstrap context as parent
+		assertNotNull(parent.getParent());
+
+		ConfigurableApplicationContext bootstrapContext = (ConfigurableApplicationContext) parent
+				.getParent();
+
+		// Bootstrap should be the root, there should be no other parent
+		assertNull(bootstrapContext.getParent());
+	}
+
+	@Test
+	public void shouldAddInOneBootstrapForSiblingsBasedHierarchy() {
+		ConfigurableApplicationContext context = new SpringApplicationBuilder()
+				.sources(RootConfiguration.class).web(false)
+				.child(BasicConfiguration.class).web(false)
+				.sibling(BasicConfiguration.class).web(false).run();
+
+		// Should be RootConfiguration based context
+		ConfigurableApplicationContext parent = (ConfigurableApplicationContext) context
+				.getParent();
+		assertEquals("rootBean", parent.getBean("rootBean", String.class));
+
+		// Parent should have the bootstrap context as parent
+		assertNotNull(parent.getParent());
+
+		ConfigurableApplicationContext bootstrapContext = (ConfigurableApplicationContext) parent
+				.getParent();
+
+		// Bootstrap should be the root, there should be no other parent
+		assertNull(bootstrapContext.getParent());
+	}
+
+	@Configuration
+	static class BasicConfiguration {
+	}
+
+	@Configuration
+	static class RootConfiguration {
+
+		@Bean
+		public String rootBean() {
+			return "rootBean";
+		}
+	}
+}