Add GemFire Support

Fixes GH PR #148 and PR #308 implementing a GemFire Adapter to support
clustered HttpSessions in Spring Session.

* Resolve SGF-373 - Implement a Spring Session Adapter for GemFire backing
a HttpSession similar to the Redis support.
* Add Spring Session annotation to enable GemFire support with
@EnableGemFireHttpSession.
* Add extesion of SpringHttpSessionConfiguration to configure GemFire using
GemFireHttpSessionConfiguration.
* Add implementation of SessionRepository to access clustered, replicated
HttpSession state in GemFire with GemFireOperationsSessionRepository.
* Utilize GemFire Data Serialization framework to both replicate
HttpSession state information as well as handle deltas.
* Utilize GemFire OQL query to lookup arbitrary Session attributes by name,
and in particular the user authenticated principal name.
* Implment unit and integration tests, and in particular, tests for both
peer-to-peer (p2p) and client/server topologies.
* Set initial Spring Data GemFire version to 1.7.2.RELEASE, which depends
on Pivotal GemFire 8.1.0.
* Add documentation, Javadoc and samples along with additional Integration
Tests.

Fixes gh-148

samples/httpsession-gemfire-clientserver/src/main/java/sample/ServerConfig.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2002-2015 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;
+
+import java.io.IOException;
+import java.util.Properties;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
+import org.springframework.data.gemfire.CacheFactoryBean;
+import org.springframework.data.gemfire.server.CacheServerFactoryBean;
+import org.springframework.session.data.gemfire.config.annotation.web.http.EnableGemFireHttpSession;
+
+import com.gemstone.gemfire.cache.Cache;
+
+// tag::class[]
+@EnableGemFireHttpSession(maxInactiveIntervalInSeconds = 30)// <1>
+public class ServerConfig {
+
+	static final int MAX_CONNECTIONS = 50;
+	static final int SERVER_PORT = 12480;
+
+	static final String SERVER_HOSTNAME = "localhost";
+
+	@Bean
+	PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
+		return new PropertySourcesPlaceholderConfigurer();
+	}
+
+	@Bean
+	Properties gemfireProperties() { // <2>
+		Properties gemfireProperties = new Properties();
+
+		gemfireProperties.setProperty("name", "GemFireClientServerHttpSessionSample");
+		gemfireProperties.setProperty("mcast-port", "0");
+		gemfireProperties.setProperty("log-level",
+			System.getProperty("sample.httpsession.gemfire.log-level", "warning"));
+		gemfireProperties.setProperty("jmx-manager", "true");
+		gemfireProperties.setProperty("jmx-manager-start", "true");
+
+		return gemfireProperties;
+	}
+
+	@Bean
+	CacheFactoryBean gemfireCache() { // <3>
+		CacheFactoryBean gemfireCache = new CacheFactoryBean();
+
+		gemfireCache.setProperties(gemfireProperties());
+		gemfireCache.setUseBeanFactoryLocator(false);
+
+		return gemfireCache;
+	}
+
+	@Bean
+	CacheServerFactoryBean gemfireCacheServer(Cache gemfireCache, // <4>
+		    @Value("${spring.session.data.gemfire.port:"+SERVER_PORT+"}") int port) {
+
+		CacheServerFactoryBean cacheServerFactory = new CacheServerFactoryBean();
+
+		cacheServerFactory.setAutoStartup(true);
+		cacheServerFactory.setBindAddress(SERVER_HOSTNAME);
+		cacheServerFactory.setCache(gemfireCache);
+		cacheServerFactory.setMaxConnections(MAX_CONNECTIONS);
+		cacheServerFactory.setPort(port);
+
+		return cacheServerFactory;
+	}
+
+	public static void main(final String[] args) throws IOException { // <5>
+		new AnnotationConfigApplicationContext(ServerConfig.class)
+			.registerShutdownHook();
+	}
+}
+// end::class[]