Add redis persisting support

- Add new StateMachineContextRepository interface.
- Add new redis module having persisting support
  for StateMachineContext.
- Extract kryo serializers into a new kryo module which
  is then shared with zookeeper and redis modules.
- We'll add redis related tests later when we figure out
  a correct pattern for integration tests.
- Fixes #110

spring-statemachine-core/src/main/java/org/springframework/statemachine/StateMachineContextRepository.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 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 org.springframework.statemachine;
+
+import org.springframework.statemachine.StateMachineContext;
+
+/**
+ * Repository interface for saving and retrieving {@link StateMachineContext} objects.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ * @param <T> The type of state machine context
+ */
+public interface StateMachineContextRepository<S, E, T extends StateMachineContext<S, E>> {
+
+	/**
+	 * Save a context.
+	 *
+	 * @param context the context
+	 * @param id the id
+	 */
+	void save(T context, String id);
+
+	/**
+	 * Gets the context.
+	 *
+	 * @param id the id
+	 * @return the context
+	 */
+	T getContext(String id);
+
+}

spring-statemachine-core/src/main/java/org/springframework/statemachine/support/RepositoryStateMachinePersist.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 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 org.springframework.statemachine.support;
+
+import org.springframework.statemachine.StateMachineContext;
+import org.springframework.statemachine.StateMachineContextRepository;
+import org.springframework.statemachine.StateMachinePersist;
+
+/**
+ * A {@link StateMachinePersist} using a generic {@link StateMachineContextRepository}
+ * for persisting {@link StateMachineContext}.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
+public class RepositoryStateMachinePersist<S, E> implements StateMachinePersist<S, E, String> {
+
+	private final StateMachineContextRepository<S, E, StateMachineContext<S,E>> repository;
+
+	/**
+	 * Instantiates a new repository state machine persist.
+	 *
+	 * @param repository the repository
+	 */
+	public RepositoryStateMachinePersist(StateMachineContextRepository<S, E, StateMachineContext<S, E>> repository) {
+		this.repository = repository;
+	}
+
+	@Override
+	public void write(StateMachineContext<S, E> context, String contextOjb) throws Exception {
+		repository.save(context, contextOjb);
+	}
+
+	@Override
+	public StateMachineContext<S, E> read(String contextOjb) throws Exception {
+		return repository.getContext(contextOjb);
+	}
+
+}