Ensure Spring Session autoconfig creates ServerProperties carefully

Without this change there can be more than one ServerProperties in a
context with different names.

Fixes gh-3476

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/SessionAutoConfiguration.java

@@ -24,9 +24,11 @@ import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
+import org.springframework.boot.autoconfigure.condition.SearchStrategy;
 import org.springframework.boot.autoconfigure.redis.RedisAutoConfiguration;
 import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.redis.connection.RedisConnectionFactory;
 import org.springframework.session.Session;
@@ -42,10 +44,10 @@ import org.springframework.session.data.redis.config.annotation.web.http.RedisHt
  */
 @Configuration
 @ConditionalOnClass(Session.class)
-@EnableConfigurationProperties(ServerProperties.class)
 @AutoConfigureAfter(RedisAutoConfiguration.class)
 public class SessionAutoConfiguration {
 
+	@EnableConfigurationProperties
 	@ConditionalOnClass(RedisConnectionFactory.class)
 	@ConditionalOnWebApplication
 	@ConditionalOnMissingBean(RedisHttpSessionConfiguration.class)
@@ -67,6 +69,19 @@ public class SessionAutoConfiguration {
 			}
 		}
 
+		@Configuration
+		@ConditionalOnMissingBean(value = ServerProperties.class, search = SearchStrategy.CURRENT)
+		// Just in case user switches off ServerPropertiesAutoConfiguration
+		public static class ServerPropertiesConfiguration {
+
+			@Bean
+			// Use the same bean name as the default one for any old webapp
+			public ServerProperties serverProperties() {
+				return new ServerProperties();
+			}
+
+		}
+
 	}
 
 }

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/session/SessionAutoConfigurationTests.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2012-2015 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.autoconfigure.session;
+
+import org.junit.After;
+import org.junit.Test;
+import org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration;
+import org.springframework.boot.autoconfigure.redis.RedisAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.ServerProperties;
+import org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration;
+import org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext;
+import org.springframework.boot.context.embedded.EmbeddedServletContainerFactory;
+import org.springframework.boot.context.embedded.MockEmbeddedServletContainerFactory;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.junit.Assert.assertNotNull;
+
+/**
+ * @author Dave Syer
+ * @since 1.3.0
+ */
+public class SessionAutoConfigurationTests {
+
+	private AnnotationConfigEmbeddedWebApplicationContext context;
+
+	@After
+	public void close() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	public void flat() throws Exception {
+		this.context = new AnnotationConfigEmbeddedWebApplicationContext();
+		this.context.register(Config.class, ServerPropertiesAutoConfiguration.class,
+				RedisAutoConfiguration.class, SessionAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		this.context.refresh();
+		ServerProperties server = this.context.getBean(ServerProperties.class);
+		assertNotNull(server);
+	}
+
+	@Test
+	public void hierarchy() throws Exception {
+		AnnotationConfigApplicationContext parent = new AnnotationConfigApplicationContext();
+		parent.register(RedisAutoConfiguration.class, SessionAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		parent.refresh();
+		this.context = new AnnotationConfigEmbeddedWebApplicationContext();
+		this.context.setParent(parent);
+		this.context.register(Config.class, ServerPropertiesAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		this.context.refresh();
+		ServerProperties server = this.context.getBean(ServerProperties.class);
+		assertNotNull(server);
+	}
+
+	@Configuration
+	protected static class Config {
+
+		@Bean
+		public EmbeddedServletContainerFactory containerFactory() {
+			return new MockEmbeddedServletContainerFactory();
+		}
+
+	}
+
+}