Ensure Redis Configured to Send Keyspace Notifications

Previously there was a possibility that Session to WebSocket mapping was
leaked if keyspace notifications were not enabled in Redis.

To resolve this the RedisHttpSessionConfiguration now ensures that Redis
is configured to enable Keyspace notifications.

Fixes gh-76 gh-81

samples/security/src/main/java/sample/EmbeddedRedisConfiguration.java

@@ -14,8 +14,12 @@ package sample;
  * License for the specific language governing permissions and limitations under
  * the License.
  */
+import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.beans.factory.support.BeanDefinitionRegistry;
+import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
@@ -33,11 +37,17 @@ import redis.embedded.RedisServer;
 public class EmbeddedRedisConfiguration {
 
     @Bean
-    public RedisServerBean redisServer() {
+    public static RedisServerBean redisServer() {
         return new RedisServerBean();
     }
 
-    class RedisServerBean implements InitializingBean, DisposableBean {
+    /**
+     * Implements BeanDefinitionRegistryPostProcessor to ensure this Bean
+     * is initialized before any other Beans. Specifically, we want to ensure
+     * that the Redis Server is started before RedisHttpSessionConfiguration
+     * attempts to enable Keyspace notifications.
+     */
+    static class RedisServerBean implements InitializingBean, DisposableBean, BeanDefinitionRegistryPostProcessor {
         private RedisServer redisServer;
 
         public void afterPropertiesSet() throws Exception {
@@ -50,5 +60,11 @@ public class EmbeddedRedisConfiguration {
                 redisServer.stop();
             }
         }
+
+        @Override
+        public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {}
+
+        @Override
+        public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
     }
-}
+}