Add ReactorSessionRepository

Fixes gh-814

spring-session-core/spring-session-core.gradle

@@ -5,6 +5,7 @@ description = "Spring Session"
 dependencies {
 	compile "org.springframework:spring-jcl"
 
+	optional "io.projectreactor:reactor-core"
 	optional "org.springframework:spring-context"
 	optional "org.springframework:spring-jdbc"
 	optional "org.springframework:spring-messaging"

spring-session-core/src/main/java/org/springframework/session/ReactorSessionRepository.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2014-2017 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 org.springframework.session;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * A repository interface for managing {@link Session} instances.
+ *
+ * @param <S> the {@link Session} type
+ * @author Rob Winch
+ * @since 2.0
+ */
+public interface ReactorSessionRepository<S extends Session> {
+
+	/**
+	 * Creates a new {@link Session} that is capable of being persisted by this
+	 * {@link ReactorSessionRepository}.
+	 *
+	 * <p>
+	 * This allows optimizations and customizations in how the {@link Session} is
+	 * persisted. For example, the implementation returned might keep track of the changes
+	 * ensuring that only the delta needs to be persisted on a save.
+	 * </p>
+	 *
+	 * @return a new {@link Session} that is capable of being persisted by this
+	 * {@link ReactorSessionRepository}
+	 */
+	Mono<S> createSession();
+
+	/**
+	 * Ensures the {@link Session} created by
+	 * {@link ReactorSessionRepository#createSession()} is saved.
+	 *
+	 * <p>
+	 * Some implementations may choose to save as the {@link Session} is updated by
+	 * returning a {@link Session} that immediately persists any changes. In this case,
+	 * this method may not actually do anything.
+	 * </p>
+	 *
+	 * @param session the {@link Session} to save
+	 */
+	Mono<Void> save(S session);
+
+	/**
+	 * Gets the {@link Session} by the {@link Session#getId()} or null if no
+	 * {@link Session} is found.
+	 *
+	 * @param id the {@link Session#getId()} to lookup
+	 * @return the {@link Session} by the {@link Session#getId()} or null if no
+	 * {@link Session} is found.
+	 */
+	Mono<S> findById(String id);
+
+	/**
+	 * Deletes the {@link Session} with the given {@link Session#getId()} or does nothing
+	 * if the {@link Session} is not found.
+	 * @param id the {@link Session#getId()} to delete
+	 */
+	Mono<Void> delete(String id);
+}