Add support for customizing session repository before initialization

This commit adds support for customizing session repository implementations (both SessionRepository and ReactiveSessionRepository) before initialization by introducing SessionRepositoryCustomizer and ReactiveSessionRepositoryCustomizer strategies.

Resolves: #1499

spring-session-core/src/main/java/org/springframework/session/config/ReactiveSessionRepositoryCustomizer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2014-2019 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
+ *
+ *      https://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.config;
+
+import org.springframework.session.ReactiveSessionRepository;
+
+/**
+ * Strategy that can be used to customize the {@link ReactiveSessionRepository} before it
+ * is fully initialized, in particular to tune its configuration.
+ *
+ * @param <T> the {@link ReactiveSessionRepository} type
+ * @author Vedran Pavic
+ * @since 2.2.0
+ */
+@FunctionalInterface
+public interface ReactiveSessionRepositoryCustomizer<T extends ReactiveSessionRepository> {
+
+	/**
+	 * Customize the {@link ReactiveSessionRepository}.
+	 * @param sessionRepository the {@link ReactiveSessionRepository} to customize
+	 */
+	void customize(T sessionRepository);
+
+}

spring-session-core/src/main/java/org/springframework/session/config/SessionRepositoryCustomizer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2014-2019 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
+ *
+ *      https://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.config;
+
+import org.springframework.session.SessionRepository;
+
+/**
+ * Strategy that can be used to customize the {@link SessionRepository} before it is fully
+ * initialized, in particular to tune its configuration.
+ *
+ * @param <T> the {@link SessionRepository} type
+ * @author Vedran Pavic
+ * @since 2.2.0
+ */
+@FunctionalInterface
+public interface SessionRepositoryCustomizer<T extends SessionRepository> {
+
+	/**
+	 * Customize the {@link SessionRepository}.
+	 * @param sessionRepository the {@link SessionRepository} to customize
+	 */
+	void customize(T sessionRepository);
+
+}