Add @NestedConfigurationProperty meta-data support

Add a @NestedConfigurationProperty annotation which can be used to
customize how configuration mete-data is generated.

Prior to this commit only inner-classes where considered nested
(see Tomcat in ServerProperties). Using this new annotation, the Ssl
property in ServerProperties can be detected as well.

See gh-1001

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -39,6 +39,7 @@ import org.springframework.boot.configurationsample.simple.SimpleTypeProperties;
 import org.springframework.boot.configurationsample.specific.InnerClassAnnotatedGetterConfig;
 import org.springframework.boot.configurationsample.specific.InnerClassProperties;
 import org.springframework.boot.configurationsample.specific.InnerClassRootConfig;
+import org.springframework.boot.configurationsample.specific.SimplePojo;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.not;
@@ -238,11 +239,8 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 						.fromSource(InnerClassProperties.class));
 		assertThat(metadata, containsProperty("config.the-second.name"));
 		assertThat(metadata, containsProperty("config.the-second.bar.name"));
-		assertThat(
-				metadata,
-				containsGroup("config.third").ofType(
-						InnerClassProperties.SimplePojo.class).fromSource(
-						InnerClassProperties.class));
+		assertThat(metadata, containsGroup("config.third").ofType(SimplePojo.class)
+				.fromSource(InnerClassProperties.class));
 		assertThat(metadata, containsProperty("config.third.value"));
 	}
 
@@ -267,6 +265,8 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 
 		static final String CONFIGURATION_PROPERTIES_ANNOTATION = "org.springframework.boot.configurationsample.ConfigurationProperties";
 
+		static final String NESTED_CONFIGURATION_PROPERTY_ANNOTATION = "org.springframework.boot.configurationsample.NestedConfigurationProperty";
+
 		private ConfigurationMetadata metadata;
 
 		@Override
@@ -274,6 +274,11 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 			return CONFIGURATION_PROPERTIES_ANNOTATION;
 		}
 
+		@Override
+		protected String nestedConfigurationPropertyAnnotation() {
+			return NESTED_CONFIGURATION_PROPERTY_ANNOTATION;
+		}
+
 		@Override
 		protected void writeMetaData(ConfigurationMetadata metadata) {
 			this.metadata = metadata;

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/NestedConfigurationProperty.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2014 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
+ *
+ *      http://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.configurationsample;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Alternative to Spring Boot's {@code @NestedConfigurationProperty} for testing (removes
+ * the need for a dependency on the real annotation).
+ *
+ * @author Stephane Nicoll
+ * @author Phillip Webb
+ * @since 1.2.0
+ */
+@Target(ElementType.FIELD)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface NestedConfigurationProperty {
+
+}

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/specific/InnerClassProperties.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.configurationsample.specific;
 
 import org.springframework.boot.configurationsample.ConfigurationProperties;
+import org.springframework.boot.configurationsample.NestedConfigurationProperty;
 
 /**
  * Demonstrate the auto-detection of a inner config classes.
@@ -30,6 +31,7 @@ public class InnerClassProperties {
 
 	private Foo second = new Foo();
 
+	@NestedConfigurationProperty
 	private final SimplePojo third = new SimplePojo();
 
 	public Foo getFirst() {
@@ -81,9 +83,4 @@ public class InnerClassProperties {
 
 	}
 
-	public static class SimplePojo extends
-			org.springframework.boot.configurationsample.specific.SimplePojo {
-
-	}
-
 }