Fix Couchbase condition on Spring Data class

This commit reverts 7e2d0fd so that the Couchbase auto-configuration can
work without Spring Data again. It also removes the `Class` reference to
a Spring Data class to a `String` reference to make sure the condition
operates properly when said class isn't on the classpath.

Closes gh-7453

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/couchbase/CouchbaseAutoConfiguration.java

@@ -34,7 +34,6 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Primary;
-import org.springframework.data.couchbase.config.CouchbaseConfigurer;
 
 /**
  * {@link EnableAutoConfiguration Auto-Configuration} for Couchbase.
@@ -44,13 +43,14 @@ import org.springframework.data.couchbase.config.CouchbaseConfigurer;
  * @since 1.4.0
  */
 @Configuration
-@ConditionalOnClass({ CouchbaseBucket.class, Cluster.class, CouchbaseConfigurer.class })
+@ConditionalOnClass({ CouchbaseBucket.class, Cluster.class })
 @Conditional(CouchbaseAutoConfiguration.CouchbaseCondition.class)
 @EnableConfigurationProperties(CouchbaseProperties.class)
 public class CouchbaseAutoConfiguration {
 
 	@Configuration
-	@ConditionalOnMissingBean({ CouchbaseConfigurer.class, CouchbaseConfiguration.class })
+	@ConditionalOnMissingBean(value = CouchbaseConfiguration.class,
+			type = "org.springframework.data.couchbase.config.CouchbaseConfigurer")
 	public static class CouchbaseConfiguration {
 
 		private final CouchbaseProperties properties;
@@ -122,8 +122,10 @@ public class CouchbaseAutoConfiguration {
 
 	/**
 	 * Determine if Couchbase should be configured. This happens if either the
-	 * user-configuration defines a {@link CouchbaseConfigurer} or if at least the
+	 * user-configuration defines a {@code CouchbaseConfigurer} or if at least the
 	 * "bootstrapHosts" property is specified.
+	 * <p>The reason why we check for the presence of {@code CouchbaseConfigurer} is
+	 * that it might use {@link CouchbaseProperties} for its internal customization.
 	 */
 	static class CouchbaseCondition extends AnyNestedCondition {
 
@@ -135,7 +137,7 @@ public class CouchbaseAutoConfiguration {
 		static class BootstrapHostsProperty {
 		}
 
-		@ConditionalOnBean(CouchbaseConfigurer.class)
+		@ConditionalOnBean(type = "org.springframework.data.couchbase.config.CouchbaseConfigurer")
 		static class CouchbaseConfigurerAvailable {
 		}