Add auto-configuration support for Spring Session

This commit adds support for automatically configuring Spring Session.
In a web application when both Spring Session and Spring Data Redis
are on the classpath, Spring Session's Redis Http Session support
will be auto-configured. The max inactive interval for Redis-backed
sessions can be configured via the environment using the existing
server.session-timeout property.

Closes gh-2318

spring-boot-samples/spring-boot-sample-session-redis/src/main/java/sample/session/redis/SampleSessionRedisApplication.java

@@ -0,0 +1,48 @@
+/*
+ * 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 sample.session.redis;
+
+import java.util.UUID;
+
+import javax.servlet.http.HttpSession;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@SpringBootApplication
+public class SampleSessionRedisApplication {
+
+	public static void main(String[] args) throws Exception {
+		SpringApplication.run(SampleSessionRedisApplication.class);
+	}
+
+	@RestController
+	static class HelloRestController {
+
+		@RequestMapping("/")
+		String uid(HttpSession session) {
+			UUID uid = (UUID) session.getAttribute("uid");
+			if (uid == null) {
+				uid = UUID.randomUUID();
+			}
+			session.setAttribute("uid", uid);
+			return uid.toString();
+		}
+	}
+}