Add base DefaultStateMachineService implementation

- First take on new interface StateMachineService with
  its default impl.
- Modify datajpapersist sample to use it.
- Relates to #432

spring-statemachine-core/src/main/java/org/springframework/statemachine/service/DefaultStateMachineService.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright 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.statemachine.service;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.springframework.statemachine.StateMachine;
+import org.springframework.statemachine.StateMachineContext;
+import org.springframework.statemachine.StateMachineException;
+import org.springframework.statemachine.StateMachinePersist;
+import org.springframework.statemachine.access.StateMachineAccess;
+import org.springframework.statemachine.access.StateMachineFunction;
+import org.springframework.statemachine.config.StateMachineFactory;
+import org.springframework.util.Assert;
+
+/**
+ * Default implementation of a {@link StateMachineService}.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
+public class DefaultStateMachineService<S, E> implements StateMachineService<S, E> {
+
+	private final StateMachineFactory<S, E> stateMachineFactory;
+	private final Map<String, StateMachine<S, E>> machines = new HashMap<String, StateMachine<S, E>>();
+	private StateMachinePersist<S, E, String> stateMachinePersist;
+
+	/**
+	 * Instantiates a new default state machine service.
+	 *
+	 * @param stateMachineFactory the state machine factory
+	 */
+	public DefaultStateMachineService(StateMachineFactory<S, E> stateMachineFactory) {
+		this(stateMachineFactory, null);
+	}
+
+	/**
+	 * Instantiates a new default state machine service.
+	 *
+	 * @param stateMachineFactory the state machine factory
+	 * @param stateMachinePersist the state machine persist
+	 */
+	public DefaultStateMachineService(StateMachineFactory<S, E> stateMachineFactory,
+			StateMachinePersist<S, E, String> stateMachinePersist) {
+		Assert.notNull(stateMachineFactory, "'stateMachineFactory' must be set");
+		this.stateMachineFactory = stateMachineFactory;
+		this.stateMachinePersist = stateMachinePersist;
+	}
+
+	@Override
+	public StateMachine<S, E> acquireStateMachine(String machineId) {
+		synchronized (machines) {
+			StateMachine<S,E> stateMachine = machines.get(machineId);
+			if (stateMachine == null) {
+				stateMachine = stateMachineFactory.getStateMachine(machineId);
+				machines.put(machineId, stateMachine);
+			}
+			if (stateMachinePersist != null) {
+				try {
+					StateMachineContext<S, E> stateMachineContext = stateMachinePersist.read(machineId);
+					return restoreStateMachine(stateMachine, stateMachineContext);
+				} catch (Exception e) {
+					throw new StateMachineException("Unable to read context from store", e);
+				}
+			} else {
+				return stateMachine;
+			}
+		}
+	}
+
+	@Override
+	public void releaseStateMachine(String machineId) {
+		synchronized (machines) {
+			StateMachine<S, E> stateMachine = machines.remove(machineId);
+			if (stateMachine != null) {
+				stateMachine.stop();
+			}
+		}
+	}
+
+	/**
+	 * Sets the state machine persist.
+	 *
+	 * @param stateMachinePersist the state machine persist
+	 */
+	public void setStateMachinePersist(StateMachinePersist<S, E, String> stateMachinePersist) {
+		this.stateMachinePersist = stateMachinePersist;
+	}
+
+	protected StateMachine<S, E> restoreStateMachine(StateMachine<S, E> stateMachine, final StateMachineContext<S, E> stateMachineContext) {
+		if (stateMachineContext == null) {
+			return stateMachine;
+		}
+		stateMachine.stop();
+		stateMachine.getStateMachineAccessor().doWithAllRegions(new StateMachineFunction<StateMachineAccess<S, E>>() {
+
+			@Override
+			public void apply(StateMachineAccess<S, E> function) {
+				function.resetStateMachine(stateMachineContext);
+			}
+		});
+		return stateMachine;
+	}
+}

spring-statemachine-core/src/main/java/org/springframework/statemachine/service/StateMachineService.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 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.statemachine.service;
+
+import org.springframework.statemachine.StateMachine;
+
+/**
+ * Service class helping to persist and restore {@link StateMachine}s
+ * in a runtime environment.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
+public interface StateMachineService<S, E> {
+
+	/**
+	 * Acquires the state machine.
+	 *
+	 * @param machineId the machine id
+	 * @return the state machine
+	 */
+	StateMachine<S, E> acquireStateMachine(String machineId);
+
+	/**
+	 * Release the state machine.
+	 *
+	 * @param machineId the machine id
+	 */
+	void releaseStateMachine(String machineId);
+}