Rework ConfigurationPropertySources

Rework the ConfigurationPropertySources and related adapter classes to
help with performance. The ConfigurationPropertySources class now only
monitors for updates when `.attach` is used. The `.get` methods now
return the adapted version, but no longer checks to see if sources have
been added or removed on each call.

This commit also fixes a few caching issues and makes both the
`PropertyMapper` implementations true static singletons.

See gh-9000

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/info/InfoPropertiesInfoContributor.java

@@ -25,7 +25,6 @@ import org.springframework.boot.context.properties.bind.Bindable;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySources;
 import org.springframework.boot.info.InfoProperties;
-import org.springframework.core.env.MutablePropertySources;
 import org.springframework.core.env.PropertySource;
 import org.springframework.util.StringUtils;
 
@@ -93,9 +92,7 @@ public abstract class InfoPropertiesInfoContributor<T extends InfoProperties>
 	 * @return the raw content
 	 */
 	protected Map<String, Object> extractContent(PropertySource<?> propertySource) {
-		MutablePropertySources sources = new MutablePropertySources();
-		sources.addFirst(propertySource);
-		return new Binder(ConfigurationPropertySources.get(sources))
+		return new Binder(ConfigurationPropertySources.from(propertySource))
 				.bind("", STRING_OBJECT_MAP).orElseGet(LinkedHashMap::new);
 	}
 

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

@@ -21,6 +21,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Properties;
 
 import javax.sql.DataSource;
 
@@ -320,9 +321,8 @@ public class EndpointAutoConfigurationTests {
 				if (!location.exists()) {
 					return;
 				}
-				MapConfigurationPropertySource source = new MapConfigurationPropertySource(
-						PropertiesLoaderUtils.loadProperties(location));
-				new Binder(source).bind("info",
+				Properties properties = PropertiesLoaderUtils.loadProperties(location);
+				new Binder(new MapConfigurationPropertySource(properties)).bind("info",
 						Bindable.of(STRING_OBJECT_MAP).withExistingValue(this.content));
 			}