Order ManagementContextConfiguration classes without loading them

Previously, ManagementContextConfiguration classes were loaded to
allow them to be ordered based on either @Order or implementing
Ordered. This had the unwanted side-effect of possibly logging
unwanted INFO messages if the reflection-based annotation
introspection failed. One cause of this was @ConditionalOnClass when
the referenced class was not on the classpath.

This commit uses the ASM-based annotation metadata reading to
determine the order of a management context configuration class based
on the @Order annotation. The classes are then sorted using a standard
OrderComparator. Note that Ordering via implemented Ordered is not
supported as it cannot be determine without loading the class.

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/ManagementContextConfiguration.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -23,6 +23,8 @@ import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
 
 /**
  * Specialized {@link Configuration @Configuration} class that defines configuration
@@ -30,8 +32,12 @@ import org.springframework.context.annotation.Configuration;
  * {@code /META-INF/spring.factories} under the
  * {@code org.springframework.boot.actuate.autoconfigure.ManagementContextConfiguration}
  * key.
+ * <p>
+ * {@code ManagementContextConfiguration} classes can be ordered using {@link Order}.
+ * Ordering by implementing {@link Ordered} is not supported and will have no effect.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @since 1.3.0
  */
 @Target(ElementType.TYPE)

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/ManagementContextConfigurationsImportSelector.java

@@ -16,19 +16,20 @@
 
 package org.springframework.boot.actuate.autoconfigure;
 
+import java.io.IOException;
 import java.util.ArrayList;
-import java.util.LinkedHashSet;
 import java.util.List;
-import java.util.Set;
+import java.util.Map;
 
 import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.context.annotation.DeferredImportSelector;
+import org.springframework.core.OrderComparator;
 import org.springframework.core.Ordered;
-import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.annotation.Order;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.core.type.AnnotationMetadata;
-import org.springframework.util.ClassUtils;
+import org.springframework.core.type.classreading.MetadataReader;
+import org.springframework.core.type.classreading.SimpleMetadataReaderFactory;
 
 /**
  * Selects configuration classes for the management context configuration. Entries are
@@ -38,6 +39,7 @@ import org.springframework.util.ClassUtils;
  *
  * @author Dave Syer
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @see ManagementContextConfiguration
  */
 @Order(Ordered.LOWEST_PRECEDENCE)
@@ -48,27 +50,41 @@ class ManagementContextConfigurationsImportSelector
 
 	@Override
 	public String[] selectImports(AnnotationMetadata metadata) {
-		// Find all possible auto configuration classes, filtering duplicates
-		List<String> names = loadFactoryNames();
-		Set<Class<?>> classes = new LinkedHashSet<Class<?>>();
-		for (String factoryName : names) {
-			classes.add(ClassUtils.resolveClassName(factoryName, this.classLoader));
+		// Find all management context configuration classes, filtering duplicates
+		List<ManagementConfiguration> configurations = getConfigurations();
+		OrderComparator.sort(configurations);
+		List<String> names = new ArrayList<String>();
+		for (ManagementConfiguration configuration : configurations) {
+			names.add(configuration.getClassName());
 		}
-		return getSortedClassNames(new ArrayList<Class<?>>(classes));
+		return names.toArray(new String[names.size()]);
 	}
 
-	protected List<String> loadFactoryNames() {
-		return SpringFactoriesLoader
-				.loadFactoryNames(ManagementContextConfiguration.class, this.classLoader);
+	private List<ManagementConfiguration> getConfigurations() {
+		SimpleMetadataReaderFactory readerFactory = new SimpleMetadataReaderFactory(
+				this.classLoader);
+		List<ManagementConfiguration> configurations = new ArrayList<ManagementConfiguration>();
+		for (String className : loadFactoryNames()) {
+			getConfiguration(readerFactory, configurations, className);
+		}
+		return configurations;
 	}
 
-	private String[] getSortedClassNames(List<Class<?>> classes) {
-		AnnotationAwareOrderComparator.sort(classes);
-		List<String> names = new ArrayList<String>();
-		for (Class<?> sourceClass : classes) {
-			names.add(sourceClass.getName());
+	private void getConfiguration(SimpleMetadataReaderFactory readerFactory,
+			List<ManagementConfiguration> configurations, String className) {
+		try {
+			MetadataReader metadataReader = readerFactory.getMetadataReader(className);
+			configurations.add(new ManagementConfiguration(metadataReader));
 		}
-		return names.toArray(new String[names.size()]);
+		catch (IOException ex) {
+			throw new RuntimeException(
+					"Failed to read annotation metadata for '" + className + "'", ex);
+		}
+	}
+
+	protected List<String> loadFactoryNames() {
+		return SpringFactoriesLoader
+				.loadFactoryNames(ManagementContextConfiguration.class, this.classLoader);
 	}
 
 	@Override
@@ -76,4 +92,39 @@ class ManagementContextConfigurationsImportSelector
 		this.classLoader = classLoader;
 	}
 
+	/**
+	 * A management configuration class which can be sorted according to {@code @Order}.
+	 */
+	private static final class ManagementConfiguration implements Ordered {
+
+		private final String className;
+
+		private final int order;
+
+		ManagementConfiguration(MetadataReader metadataReader) {
+			AnnotationMetadata annotationMetadata = metadataReader
+					.getAnnotationMetadata();
+			this.order = readOrder(annotationMetadata);
+			this.className = metadataReader.getClassMetadata().getClassName();
+		}
+
+		private int readOrder(AnnotationMetadata annotationMetadata) {
+			Map<String, Object> attributes = annotationMetadata
+					.getAnnotationAttributes(Order.class.getName());
+			Integer order = (attributes == null ? null
+					: (Integer) attributes.get("value"));
+			return (order == null ? Ordered.LOWEST_PRECEDENCE : order);
+		}
+
+		public String getClassName() {
+			return this.className;
+		}
+
+		@Override
+		public int getOrder() {
+			return this.order;
+		}
+
+	}
+
 }

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

@@ -29,6 +29,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link ManagementContextConfigurationsImportSelector}.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  */
 public class ManagementContextConfigurationsImportSelectorTests {
 
@@ -37,7 +38,7 @@ public class ManagementContextConfigurationsImportSelectorTests {
 		String[] imports = new TestManagementContextConfigurationsImportSelector()
 				.selectImports(null);
 		assertThat(imports).containsExactly(A.class.getName(), B.class.getName(),
-				C.class.getName());
+				C.class.getName(), D.class.getName());
 	}
 
 	private static class TestManagementContextConfigurationsImportSelector
@@ -45,7 +46,8 @@ public class ManagementContextConfigurationsImportSelectorTests {
 
 		@Override
 		protected List<String> loadFactoryNames() {
-			return Arrays.asList(C.class.getName(), A.class.getName(), B.class.getName());
+			return Arrays.asList(C.class.getName(), A.class.getName(), D.class.getName(),
+					B.class.getName());
 		}
 
 	}
@@ -65,4 +67,8 @@ public class ManagementContextConfigurationsImportSelectorTests {
 
 	}
 
+	static class D {
+
+	}
+
 }