开源状态机引擎，在实战中可以放心使用

### Squirrel-Foundation 状态机开源项目介绍

**Squirrel-Foundation** 是一个轻量级、灵活、可扩展、易于使用且类型安全的 Java 状态机实现，适用于企业级应用。它提供了多种方式来定义状态机，包括注解声明和 Fluent API，并且支持状态转换、状态动作、上下文传递等功能。

#### GitHub 地址
- **项目地址**：[https://github.com/hekailiang/squirrel](https://github.com/hekailiang/squirrel)

#### 使用说明

##### 1. 添加依赖
Squirrel-Foundation 已发布到 Maven 中央仓库，可以通过以下方式添加依赖：
- **最新发布版本**：
    ```xml
    <dependency>
        <groupId>org.squirrelframework</groupId>
        <artifactId>squirrel-foundation</artifactId>
        <version>0.3.10</version>
    </dependency>
    ```
- **最新快照版本**：
    ```xml
    <dependency>
        <groupId>org.squirrelframework</groupId>
        <artifactId>squirrel-foundation</artifactId>
        <version>0.3.11-SNAPSHOT</version>
    </dependency>
    ```

##### 2. 快速开始
以下是一个简单的示例代码，展示如何创建和使用状态机：
```java
public class QuickStartSample {
    // 定义状态机事件
    enum FSMEvent {
        ToA, ToB, ToC, ToD
    }

    // 定义状态机类
    @StateMachineParameters(stateType = String.class, eventType = FSMEvent.class, contextType = Integer.class)
    static class StateMachineSample extends AbstractUntypedStateMachine {
        protected void fromAToB(String from, String to, FSMEvent event, Integer context) {
            System.out.println("Transition from '" + from + "' to '" + to + "' on event '" + event +
                    "' with context '" + context + "'.");
        }

        protected void ontoB(String from, String to, FSMEvent event, Integer context) {
            System.out.println("Entry State '" + to + "'.");
        }
    }

    public static void main(String[] args) {
        // 构建状态转换
        UntypedStateMachineBuilder builder = StateMachineBuilderFactory.create(StateMachineSample.class);
        builder.externalTransition().from("A").to("B").on(FSMEvent.ToB).callMethod("fromAToB");
        builder.onEntry("B").callMethod("ontoB");

        // 使用状态机
        UntypedStateMachine fsm = builder.newStateMachine("A");
        fsm.fire(FSMEvent.ToB, 10);

        System.out.println("Current state is " + fsm.getCurrentState());
    }
}
```

##### 3. 定义状态机
Squirrel-Foundation 支持通过 Fluent API 和注解声明两种方式定义状态机：
- **Fluent API**：
    ```java
    builder.externalTransition().from(MyState.A).to(MyState.B).on(MyEvent.GoToB);
    ```
- **注解声明**：
    ```java
    @States({
        @State(name = "A", entryCallMethod = "entryStateA", exitCallMethod = "exitStateA"),
        @State(name = "B", entryCallMethod = "entryStateB", exitCallMethod = "exitStateB")
    })
    @Transitions({
        @Transit(from = "A", to = "B", on = "GoToB", callMethod = "stateAToStateBOnGotoB"),
        @Transit(from = "A", to = "A", on = "WithinA", callMethod = "stateAToStateAOnWithinA", type = TransitionType.INTERNAL)
    })
    interface MyStateMachine extends StateMachine<MyStateMachine, MyState, MyEvent, MyContext> {
        void entryStateA(MyState from, MyState to, MyEvent event, MyContext context);
        void stateAToStateBOnGotoB(MyState from, MyState to, MyEvent event, MyContext context);
        void stateAToStateAOnWithinA(MyState from, MyState to, MyEvent event, MyContext context);
        void exitStateA(MyState from, MyState to, MyEvent event, MyContext context);
    }
    ```

##### 4. 高级特性
- **转换扩展方法**：可以在状态转换时扩展自定义逻辑。
    ```java
    protected void afterTransitionCompleted(S fromState, S toState, E event, C context) {
        // 自定义逻辑
    }
    ```
- **异步事件处理**：通过 `@AsyncExecute` 注解可以将事件处理逻辑异步执行。
    ```java
    public class DeclarativeListener {
        @OnTransitionBegin
        @AsyncExecute
        public void onTransitionBegin(...) {
            // 异步处理逻辑
        }
    }
    ```

##### 5. 与其他框架集成
Squirrel-Foundation 可以与 Spring 框架集成，通过注册一个后处理器来自动注入依赖：
```java
@Component
public class StateMachineAutowireProcessor implements SquirrelPostProcessor<StateMachine>, ApplicationContextAware {
    private ApplicationContext applicationContext;

    public StateMachineAutowireProcessor() {
        SquirrelPostProcessorProvider.getInstance().register(StateMachine.class, this);
    }

    @Override
    public void postProcess(StateMachine stateMachine) {
        AutowireCapableBeanFactory autowireCapableBeanFactory = applicationContext.getAutowireCapableBeanFactory();
        autowireCapableBeanFactory.autowireBean(stateMachine);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}
```

更多使用细节和高级特性可以参考 [Squirrel-Foundation 官方文档](https://hekailiang.github.io/squirrel/) 或其 [GitHub 仓库](https://github.com/hekailiang/squirrel)。