Add config properties before default properties

Update ConfigFileApplicationListener so that configuration properties
are added before `defaultProperties` if they exist.

Fixes gh-4362

spring-boot/src/main/java/org/springframework/boot/context/config/ConfigFileApplicationListener.java

@@ -569,9 +569,20 @@ public class ConfigFileApplicationListener implements EnvironmentPostProcessor,
 			for (PropertySource<?> item : sources) {
 				reorderedSources.add(item);
 			}
-			// Maybe we should add before the DEFAULT_PROPERTIES if it exists?
-			this.environment.getPropertySources()
-					.addLast(new ConfigurationPropertySources(reorderedSources));
+			addConfigurationProperties(
+					new ConfigurationPropertySources(reorderedSources));
+		}
+
+		private void addConfigurationProperties(
+				ConfigurationPropertySources configurationSources) {
+			MutablePropertySources existingSources = this.environment
+					.getPropertySources();
+			if (existingSources.contains(DEFAULT_PROPERTIES)) {
+				existingSources.addBefore(DEFAULT_PROPERTIES, configurationSources);
+			}
+			else {
+				existingSources.addLast(configurationSources);
+			}
 		}
 
 	}

spring-boot/src/test/java/org/springframework/boot/context/config/ConfigFileApplicationListenerTests.java

@@ -765,6 +765,18 @@ public class ConfigFileApplicationListenerTests {
 		assertThat(property, equalTo("false"));
 	}
 
+	@Test
+	public void addBeforeDefaultProperties() throws Exception {
+		MapPropertySource defaultSource = new MapPropertySource("defaultProperties",
+				Collections.<String, Object>singletonMap("the.property",
+						"fromdefaultproperties"));
+		this.environment.getPropertySources().addFirst(defaultSource);
+		this.initializer.setSearchNames("testproperties");
+		this.initializer.postProcessEnvironment(this.environment, this.application);
+		String property = this.environment.getProperty("the.property");
+		assertThat(property, equalTo("frompropertiesfile"));
+	}
+
 	private static Matcher<? super ConfigurableEnvironment> containsPropertySource(
 			final String sourceName) {
 		return new TypeSafeDiagnosingMatcher<ConfigurableEnvironment>() {