Ensure that environment post processors are ordered correctly

Previously, ConfigFileApplicationListener would always add itself to the
end of the list of environment post processors loaded via
spring.factories. This meant that its order (highest precedence + 10)
would not be honoured and it would only be in the right place in the
list if any other post processors happened to have a higher precedence.

This commit updates ConfigFileApplicationListener to sort the list of
post processors using AnnotationAwareOrderComparator once its added
itself to the list.

Closes gh-4595

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

@@ -47,6 +47,7 @@ import org.springframework.context.ApplicationListener;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.ConfigurationClassPostProcessor;
 import org.springframework.core.Ordered;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.core.env.ConfigurableEnvironment;
@@ -153,16 +154,20 @@ public class ConfigFileApplicationListener implements EnvironmentPostProcessor,
 
 	private void onApplicationEnvironmentPreparedEvent(
 			ApplicationEnvironmentPreparedEvent event) {
-		List<EnvironmentPostProcessor> postProcessors = SpringFactoriesLoader
-				.loadFactories(EnvironmentPostProcessor.class,
-						getClass().getClassLoader());
+		List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
 		postProcessors.add(this);
+		AnnotationAwareOrderComparator.sort(postProcessors);
 		for (EnvironmentPostProcessor postProcessor : postProcessors) {
 			postProcessor.postProcessEnvironment(event.getEnvironment(),
 					event.getSpringApplication());
 		}
 	}
 
+	List<EnvironmentPostProcessor> loadPostProcessors() {
+		return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
+				getClass().getClassLoader());
+	}
+
 	@Override
 	public void postProcessEnvironment(ConfigurableEnvironment environment,
 			SpringApplication application) {

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

@@ -44,8 +44,10 @@ import org.springframework.beans.CachedIntrospectionResults;
 import org.springframework.boot.Banner;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.context.config.ConfigFileApplicationListener.ConfigurationPropertySources;
+import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
 import org.springframework.boot.context.event.ApplicationPreparedEvent;
 import org.springframework.boot.env.EnumerableCompositePropertySource;
+import org.springframework.boot.env.EnvironmentPostProcessor;
 import org.springframework.boot.test.EnvironmentTestUtils;
 import org.springframework.boot.test.OutputCapture;
 import org.springframework.context.ConfigurableApplicationContext;
@@ -53,6 +55,8 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Profile;
 import org.springframework.context.annotation.PropertySource;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.MapPropertySource;
 import org.springframework.core.env.MutablePropertySources;
@@ -67,6 +71,7 @@ import org.springframework.util.StringUtils;
 import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
@@ -445,6 +450,13 @@ public class ConfigFileApplicationListenerTests {
 		validateProfilePrecedence(null, "other", "dev");
 	}
 
+	@Test
+	public void postProcessorsAreOrderedCorrectly() {
+		TestConfigFileApplicationListener testListener = new TestConfigFileApplicationListener();
+		testListener.onApplicationEvent(new ApplicationEnvironmentPreparedEvent(
+				this.application, new String[0], this.environment));
+	}
+
 	private void validateProfilePrecedence(String... profiles) {
 		ApplicationPreparedEvent event = new ApplicationPreparedEvent(
 				new SpringApplication(), new String[0],
@@ -868,4 +880,27 @@ public class ConfigFileApplicationListenerTests {
 
 	}
 
+	private static class TestConfigFileApplicationListener
+			extends ConfigFileApplicationListener {
+
+		@Override
+		List<EnvironmentPostProcessor> loadPostProcessors() {
+			return new ArrayList<EnvironmentPostProcessor>(
+					Arrays.asList(new LowestPrecedenceEnvironmentPostProcessor()));
+		}
+
+	}
+
+	@Order(Ordered.LOWEST_PRECEDENCE)
+	private static class LowestPrecedenceEnvironmentPostProcessor
+			implements EnvironmentPostProcessor {
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment,
+				SpringApplication application) {
+			assertThat(environment.getPropertySources().size(), is(equalTo(4)));
+		}
+
+	}
+
 }