Improve configuration properties logging

Update ConfigurationPropertiesBindingPostProcessor with improved logging
when multiple PropertySourcesPlaceholderConfigurer beans are found.

See gh-6457

spring-boot/src/main/java/org/springframework/boot/context/properties/ConfigurationPropertiesBindingPostProcessor.java

@@ -22,6 +22,9 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanCreationException;
 import org.springframework.beans.factory.BeanFactory;
@@ -87,6 +90,9 @@ public class ConfigurationPropertiesBindingPostProcessor
 	private static final String[] VALIDATOR_CLASSES = { "javax.validation.Validator",
 			"javax.validation.ValidatorFactory" };
 
+	private static final Log logger = LogFactory
+			.getLog(ConfigurationPropertiesBindingPostProcessor.class);
+
 	private ConfigurationBeanFactoryMetaData beans = new ConfigurationBeanFactoryMetaData();
 
 	private PropertySources propertySources;
@@ -254,6 +260,8 @@ public class ConfigurationPropertiesBindingPostProcessor
 			return new FlatPropertySources(propertySources);
 		}
 		// empty, so not very useful, but fulfils the contract
+		logger.warn("Unable to obtain PropertySources from "
+				+ "PropertySourcesPlaceholderConfigurer or Environment");
 		return new MutablePropertySources();
 	}
 
@@ -267,6 +275,11 @@ public class ConfigurationPropertiesBindingPostProcessor
 			if (beans.size() == 1) {
 				return beans.values().iterator().next();
 			}
+			if (beans.size() > 1 && logger.isWarnEnabled()) {
+				logger.warn("Multiple PropertySourcesPlaceholderConfigurer "
+						+ "beans registered " + beans.keySet()
+						+ ", falling back to Environment");
+			}
 		}
 		return null;
 	}

spring-boot/src/test/java/org/springframework/boot/context/properties/ConfigurationPropertiesBindingPostProcessorTests.java

@@ -34,6 +34,7 @@ import org.springframework.beans.factory.annotation.Value;
 import org.springframework.beans.factory.support.AbstractBeanDefinition;
 import org.springframework.beans.factory.support.GenericBeanDefinition;
 import org.springframework.boot.bind.RelaxedBindingNotWritablePropertyException;
+import org.springframework.boot.testutil.InternalOutputCapture;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -61,6 +62,9 @@ public class ConfigurationPropertiesBindingPostProcessorTests {
 	@Rule
 	public ExpectedException thrown = ExpectedException.none();
 
+	@Rule
+	public InternalOutputCapture output = new InternalOutputCapture();
+
 	private AnnotationConfigApplicationContext context;
 
 	@After
@@ -336,6 +340,15 @@ public class ConfigurationPropertiesBindingPostProcessorTests {
 		this.context.refresh();
 	}
 
+	@Test
+	public void multiplePropertySourcesPlaceholderConfigurer() throws Exception {
+		this.context = new AnnotationConfigApplicationContext();
+		this.context.register(MultiplePropertySourcesPlaceholderConfigurer.class);
+		this.context.refresh();
+		assertThat(this.output.toString()).contains(
+				"Multiple PropertySourcesPlaceholderConfigurer beans registered");
+	}
+
 	private void assertBindingFailure(int errorCount) {
 		try {
 			this.context.refresh();
@@ -732,6 +745,22 @@ public class ConfigurationPropertiesBindingPostProcessorTests {
 
 	}
 
+	@Configuration
+	@EnableConfigurationProperties
+	public static class MultiplePropertySourcesPlaceholderConfigurer {
+
+		@Bean
+		public static PropertySourcesPlaceholderConfigurer configurer1() {
+			return new PropertySourcesPlaceholderConfigurer();
+		}
+
+		@Bean
+		public static PropertySourcesPlaceholderConfigurer configurer2() {
+			return new PropertySourcesPlaceholderConfigurer();
+		}
+
+	}
+
 	public static class PropertyWithoutConfigurationPropertiesAnnotation {
 
 		private String name;