Make Flyway and Liquibase endpoints conditional on a single candidate

Previously, auto-configuration of the Flyway and Liquibase endpoints
would fail if there were multiple Flyway or Spring Liquibase beans
in the application context.

This commit updates them so that they are now conditional on a single
candidate.

Closes gh-6609

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/EndpointAutoConfiguration.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -57,6 +57,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionEvaluationRepor
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnSingleCandidate;
 import org.springframework.boot.autoconfigure.condition.SearchStrategy;
 import org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration;
 import org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration;
@@ -175,7 +176,7 @@ public class EndpointAutoConfiguration {
 	}
 
 	@Configuration
-	@ConditionalOnBean(Flyway.class)
+	@ConditionalOnSingleCandidate(Flyway.class)
 	@ConditionalOnClass(Flyway.class)
 	static class FlywayEndpointConfiguration {
 
@@ -188,7 +189,7 @@ public class EndpointAutoConfiguration {
 	}
 
 	@Configuration
-	@ConditionalOnBean(SpringLiquibase.class)
+	@ConditionalOnSingleCandidate(SpringLiquibase.class)
 	@ConditionalOnClass(SpringLiquibase.class)
 	static class LiquibaseEndpointConfiguration {
 

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/autoconfigure/EndpointAutoConfigurationTests.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -20,6 +20,8 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Map;
 
+import liquibase.integration.spring.SpringLiquibase;
+import org.flywaydb.core.Flyway;
 import org.junit.After;
 import org.junit.Test;
 
@@ -47,10 +49,14 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link EndpointAutoConfiguration}.
@@ -173,6 +179,16 @@ public class EndpointAutoConfigurationTests {
 		assertEquals(1, endpoint.invoke().size());
 	}
 
+	@Test
+	public void flywayEndpointIsDisabledWhenThereAreMultipleFlywayBeans() {
+		this.context = new AnnotationConfigApplicationContext();
+		this.context.register(MultipleFlywayBeansConfig.class,
+				EndpointAutoConfiguration.class);
+		this.context.refresh();
+		assertThat(this.context.getBeansOfType(FlywayEndpoint.class).size(),
+				is(equalTo(0)));
+	}
+
 	@Test
 	public void testLiquibaseEndpoint() {
 		this.context = new AnnotationConfigApplicationContext();
@@ -184,6 +200,16 @@ public class EndpointAutoConfigurationTests {
 		assertEquals(1, endpoint.invoke().size());
 	}
 
+	@Test
+	public void liquibaseEndpointIsDisabledWhenThereAreMultipleSpringLiquibaseBeans() {
+		this.context = new AnnotationConfigApplicationContext();
+		this.context.register(MultipleLiquibaseBeansConfig.class,
+				EndpointAutoConfiguration.class);
+		this.context.refresh();
+		assertThat(this.context.getBeansOfType(LiquibaseEndpoint.class).size(),
+				is(equalTo(0)));
+	}
+
 	private void load(Class<?>... config) {
 		this.context = new AnnotationConfigApplicationContext();
 		this.context.register(config);
@@ -205,4 +231,35 @@ public class EndpointAutoConfigurationTests {
 		}
 
 	}
+
+	@Configuration
+	static class MultipleFlywayBeansConfig {
+
+		@Bean
+		Flyway flywayOne() {
+			return mock(Flyway.class);
+		}
+
+		@Bean
+		Flyway flywayTwo() {
+			return mock(Flyway.class);
+		}
+
+	}
+
+	@Configuration
+	static class MultipleLiquibaseBeansConfig {
+
+		@Bean
+		SpringLiquibase liquibaseOne() {
+			return mock(SpringLiquibase.class);
+		}
+
+		@Bean
+		SpringLiquibase liquibaseTwo() {
+			return mock(SpringLiquibase.class);
+		}
+
+	}
+
 }