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-p2p-xml/src/main/webapp/WEB-INF/spring/session.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	   xmlns:context="http://www.springframework.org/schema/context"
+	   xmlns:gfe="http://www.springframework.org/schema/gemfire"
+	   xmlns:util="http://www.springframework.org/schema/util"
+	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	   xsi:schemaLocation="
+	   	http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
+		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
+        http://www.springframework.org/schema/gemfire http://www.springframework.org/schema/gemfire/spring-gemfire.xsd
+		http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd
+">
+
+	<!-- tag::beans[] -->
+	<!--1-->
+	<context:annotation-config/>
+	<context:property-placeholder/>
+
+	<bean class="org.springframework.session.data.gemfire.config.annotation.web.http.GemFireHttpSessionConfiguration"/>
+
+	<!--2-->
+	<util:properties id="gemfireProperties">
+		<prop key="name">GemFireP2PHttpSessionXmlSample</prop>
+		<prop key="mcast-port">0</prop>
+		<prop key="log-level">${sample.httpsession.gemfire.log-level:warning}</prop>
+		<prop key="jmx-manager">true</prop>
+		<prop key="jmx-manager-start">true</prop>
+	</util:properties>
+
+	<!--3-->
+	<gfe:cache properties-ref="gemfireProperties" use-bean-factory-locator="false"/>
+	<!-- end::beans[] -->
+
+</beans>

samples/httpsession-gemfire-p2p-xml/src/main/webapp/WEB-INF/web.xml

@@ -0,0 +1,55 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
+		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
+	<!--
+	- Location of the XML file that defines the root application context
+	- Applied by ContextLoaderListener.
+	-->
+	<!-- tag::context-param[] -->
+	<context-param>
+		<param-name>contextConfigLocation</param-name>
+		<param-value>
+			/WEB-INF/spring/*.xml
+		</param-value>
+	</context-param>
+	<!-- end::context-param[] -->
+
+	<!-- tag::springSessionRepositoryFilter[] -->
+	<filter>
+		<filter-name>springSessionRepositoryFilter</filter-name>
+		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
+	</filter>
+	<filter-mapping>
+		<filter-name>springSessionRepositoryFilter</filter-name>
+		<url-pattern>/*</url-pattern>
+	</filter-mapping>
+	<!-- end::springSessionRepositoryFilter[] -->
+
+	<!--
+	- Loads the root application context of this web app at startup.
+	- The application context is then available via
+	- WebApplicationContextUtils.getWebApplicationContext(servletContext).
+	-->
+	<!-- tag::listeners[] -->
+	<listener>
+		<listener-class>
+			org.springframework.web.context.ContextLoaderListener
+		</listener-class>
+	</listener>
+	<!-- end::listeners[] -->
+
+	<servlet>
+		<servlet-name>session</servlet-name>
+		<servlet-class>sample.SessionServlet</servlet-class>
+	</servlet>
+
+	<servlet-mapping>
+		<servlet-name>session</servlet-name>
+		<url-pattern>/session</url-pattern>
+	</servlet-mapping>
+
+	<welcome-file-list>
+		<welcome-file>index.jsp</welcome-file>
+	</welcome-file-list>
+</web-app>

samples/httpsession-gemfire-p2p-xml/src/main/webapp/index.jsp

@@ -0,0 +1,48 @@
+<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <title>Session Attributes</title>
+    <link rel="stylesheet" href="assets/bootstrap.min.css">
+    <style type="text/css">
+        body {
+            padding: 1em;
+        }
+    </style>
+</head>
+<body>
+    <div class="container">
+        <h1>Description</h1>
+        <p>This application demonstrates how to use a GemFire instance to back your session. Notice that there is no JSESSIONID cookie. We are also able to customize the way of identifying what the requested session id is.</p>
+
+        <h1>Try it</h1>
+
+        <form class="form-inline" role="form" action="./session" method="post">
+            <label for="attributeName">Attribute Name</label>
+            <input id="attributeName" type="text" name="attributeName"/>
+            <label for="attributeValue">Attribute Value</label>
+            <input id="attributeValue" type="text" name="attributeValue"/>
+            <input type="submit" value="Set Attribute"/>
+        </form>
+
+        <hr/>
+
+        <table class="table table-striped">
+            <thead>
+            <tr>
+                <th>Attribute Name</th>
+                <th>Attribute Value</th>
+            </tr>
+            </thead>
+            <tbody>
+            <c:forEach items="${sessionScope}" var="attr">
+                <tr>
+                    <td><c:out value="${attr.key}"/></td>
+                    <td><c:out value="${attr.value}"/></td>
+                </tr>
+            </c:forEach>
+            </tbody>
+        </table>
+    </div>
+</body>
+</html>