Improve Spring Session sample

This commit improves the Spring Session sample by providing multiple
build profiles that make it possible to easily try out different session
stores. By default, JDBC session store backed by an in-memory embedded H2
database is used.

See gh-10351

spring-boot-samples/spring-boot-sample-session/src/main/java/sample/session/HelloRestController.java

@@ -0,0 +1,39 @@
+/*
+ * 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.
+ * 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.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+public class HelloRestController {
+
+	@GetMapping("/")
+	String uid(HttpSession session) {
+		UUID uid = (UUID) session.getAttribute("uid");
+		if (uid == null) {
+			uid = UUID.randomUUID();
+		}
+		session.setAttribute("uid", uid);
+		return uid.toString();
+	}
+
+}

spring-boot-samples/spring-boot-sample-session/src/main/java/sample/session/SampleSessionApplication.java

@@ -0,0 +1,29 @@
+/*
+ * 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.
+ * 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 org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SampleSessionApplication {
+
+	public static void main(String[] args) throws Exception {
+		SpringApplication.run(SampleSessionApplication.class);
+	}
+
+}