Extract DefaultPropertiesPropertySource class

Extract `DefaultPropertiesPropertySource` from `SpringApplication` so
that logic can be easily accessed by other classes. Specifically the
property source name and logic to move the source to the end of the
list needs to be called from several places.

Closes gh-22520

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -47,6 +47,7 @@ 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.convert.ApplicationConversionService;
+import org.springframework.boot.env.DefaultPropertiesPropertySource;
 import org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext;
 import org.springframework.boot.web.reactive.context.StandardReactiveWebEnvironment;
 import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
@@ -68,7 +69,6 @@ import org.springframework.core.env.CommandLinePropertySource;
 import org.springframework.core.env.CompositePropertySource;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;
-import org.springframework.core.env.MapPropertySource;
 import org.springframework.core.env.MutablePropertySources;
 import org.springframework.core.env.PropertySource;
 import org.springframework.core.env.SimpleCommandLinePropertySource;
@@ -351,6 +351,7 @@ public class SpringApplication {
 		configureEnvironment(environment, applicationArguments.getSourceArgs());
 		ConfigurationPropertySources.attach(environment);
 		listeners.environmentPrepared(environment);
+		DefaultPropertiesPropertySource.moveToEnd(environment);
 		bindToSpringApplication(environment);
 		if (!this.isCustomEnvironment) {
 			environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
@@ -499,9 +500,7 @@ public class SpringApplication {
 	 */
 	protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
 		MutablePropertySources sources = environment.getPropertySources();
-		if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
+		DefaultPropertiesPropertySource.ifNotEmpty(this.defaultProperties, sources::addLast);
-			sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
-		}
 		if (this.addCommandLineProperties && args.length > 0) {
 			String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
 			if (sources.contains(name)) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/DefaultPropertiesPropertySource.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.boot.env;
+
+import java.util.Map;
+import java.util.function.Consumer;
+
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.Environment;
+import org.springframework.core.env.MapPropertySource;
+import org.springframework.core.env.MutablePropertySources;
+import org.springframework.core.env.PropertySource;
+import org.springframework.util.CollectionUtils;
+
+/**
+ * {@link MapPropertySource} containing default properties contributed directly to a
+ * {@code SpringApplication}. By convention, the {@link DefaultPropertiesPropertySource}
+ * is always the last property source in the {@link Environment}.
+ *
+ * @author Phillip Webb
+ * @since 2.4.0
+ */
+public class DefaultPropertiesPropertySource extends MapPropertySource {
+
+	/**
+	 * The name of the 'default properties' property source.
+	 */
+	public static final String NAME = "defaultProperties";
+
+	/**
+	 * Create a new {@link DefaultPropertiesPropertySource} with the given {@code Map}
+	 * source.
+	 * @param source the source map
+	 */
+	public DefaultPropertiesPropertySource(Map<String, Object> source) {
+		super(NAME, source);
+	}
+
+	/**
+	 * Return {@code true} if the given source is named 'defaultProperties'.
+	 * @param propertySource the property source to check
+	 * @return {@code true} if the name matches
+	 */
+	public static boolean hasMatchingName(PropertySource<?> propertySource) {
+		return (propertySource != null) && propertySource.getName().equals(NAME);
+	}
+
+	/**
+	 * Create a consume a new {@link DefaultPropertiesPropertySource} instance if the
+	 * provided source is not empty.
+	 * @param source the {@code Map} source
+	 * @param action the action used to consume the
+	 * {@link DefaultPropertiesPropertySource}
+	 */
+	public static void ifNotEmpty(Map<String, Object> source, Consumer<DefaultPropertiesPropertySource> action) {
+		if (!CollectionUtils.isEmpty(source) && action != null) {
+			action.accept(new DefaultPropertiesPropertySource(source));
+		}
+	}
+
+	/**
+	 * Move the 'defaultProperties' property source so that it's the last source in the
+	 * given {@link ConfigurableEnvironment}.
+	 * @param environment the environment to update
+	 */
+	public static void moveToEnd(ConfigurableEnvironment environment) {
+		moveToEnd(environment.getPropertySources());
+	}
+
+	/**
+	 * Move the 'defaultProperties' property source so that it's the last source in the
+	 * given {@link MutablePropertySources}.
+	 * @param propertySources the property sources to update
+	 */
+	public static void moveToEnd(MutablePropertySources propertySources) {
+		PropertySource<?> propertySource = propertySources.remove(NAME);
+		if (propertySource != null) {
+			propertySources.addLast(propertySource);
+		}
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/DefaultPropertiesPropertySourceTests.java

@@ -0,0 +1,123 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.boot.env;
+
+import java.util.Collections;
+import java.util.function.Consumer;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import org.springframework.core.env.MutablePropertySources;
+import org.springframework.core.env.PropertySource;
+import org.springframework.mock.env.MockEnvironment;
+import org.springframework.mock.env.MockPropertySource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoInteractions;
+
+/**
+ * Tests for {@link DefaultPropertiesPropertySource}.
+ *
+ * @author Phillip Webb
+ */
+class DefaultPropertiesPropertySourceTests {
+
+	@Mock
+	private Consumer<DefaultPropertiesPropertySource> action;
+
+	@Captor
+	private ArgumentCaptor<DefaultPropertiesPropertySource> captor;
+
+	@BeforeEach
+	void setup() {
+		MockitoAnnotations.initMocks(this);
+	}
+
+	@Test
+	void nameIsDefaultProperties() {
+		assertThat(DefaultPropertiesPropertySource.NAME).isEqualTo("defaultProperties");
+	}
+
+	@Test
+	void createCreatesSource() {
+		DefaultPropertiesPropertySource propertySource = new DefaultPropertiesPropertySource(
+				Collections.singletonMap("spring", "boot"));
+		assertThat(propertySource.getName()).isEqualTo("defaultProperties");
+		assertThat(propertySource.getProperty("spring")).isEqualTo("boot");
+	}
+
+	@Test
+	void hasMatchingNameWhenNameMatchesReturnsTrue() {
+		MockPropertySource propertySource = new MockPropertySource("defaultProperties");
+		assertThat(DefaultPropertiesPropertySource.hasMatchingName(propertySource)).isTrue();
+	}
+
+	@Test
+	void hasMatchingNameWhenNameDoesNotMatchReturnsFalse() {
+		MockPropertySource propertySource = new MockPropertySource("normalProperties");
+		assertThat(DefaultPropertiesPropertySource.hasMatchingName(propertySource)).isFalse();
+	}
+
+	@Test
+	void hasMatchingNameWhenPropertySourceIsNullReturnsFalse() {
+		assertThat(DefaultPropertiesPropertySource.hasMatchingName(null)).isFalse();
+	}
+
+	@Test
+	void ifNotEmptyWhenNullDoesNotCallAction() {
+		DefaultPropertiesPropertySource.ifNotEmpty(null, this.action);
+		verifyNoInteractions(this.action);
+	}
+
+	@Test
+	void ifNotEmptyWhenEmptyDoesNotCallAction() {
+		DefaultPropertiesPropertySource.ifNotEmpty(Collections.emptyMap(), this.action);
+		verifyNoInteractions(this.action);
+	}
+
+	@Test
+	void ifNotEmptyHasValueCallsAction() {
+		DefaultPropertiesPropertySource.ifNotEmpty(Collections.singletonMap("spring", "boot"), this.action);
+		verify(this.action).accept(this.captor.capture());
+		assertThat(this.captor.getValue().getProperty("spring")).isEqualTo("boot");
+	}
+
+	@Test
+	void moveToEndWhenNotPresentDoesNothing() {
+		MockEnvironment environment = new MockEnvironment();
+		DefaultPropertiesPropertySource.moveToEnd(environment);
+	}
+
+	@Test
+	void moveToEndWhenPresentMovesToEnd() {
+		MockEnvironment environment = new MockEnvironment();
+		MutablePropertySources propertySources = environment.getPropertySources();
+		propertySources.addLast(new DefaultPropertiesPropertySource(Collections.singletonMap("spring", "boot")));
+		propertySources.addLast(new MockPropertySource("test"));
+		DefaultPropertiesPropertySource.moveToEnd(environment);
+		String[] names = propertySources.stream().map(PropertySource::getName).toArray(String[]::new);
+		assertThat(names).containsExactly(MockPropertySource.MOCK_PROPERTIES_PROPERTY_SOURCE_NAME, "test",
+				DefaultPropertiesPropertySource.NAME);
+	}
+
+}