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我有一个使用 CDI 的项目。具有状态列表的容器托管服务类。

@ApplicationScoped
public class StateService {

    @Inject
    MailService mailService;

    //Inject some other stuff

    private Map<String, State> state = new HashMap<String, State>();

    public void makeStateTransition(StateChange stateChange) {
        State currentState = state.get(stateChange.getKey());
        switch (currentState.stateType) {
            case STATE1:
                handleState1Transition(stateChange);
            case STATE2:
                handleState2Transition(stateChange);
            case STATE3:
                handleState3Transition(stateChange);
        }
    }

    private void handleState1Transition(StateChange stateChange) {
        //Do some stuff to handle state and use injected mailsender to send some email
        mailService.sendEmail("Send some email");
        //if some criteria is right create a new state and set it in the map
        State newState = new State();
        //Set some variable
        state.put(stateChange.getKey(), newState);
    }

    private void handleState2Transition(StateChange stateChange) {
        //Do stuff similar to above, maybe use other injected fields
    }

    private void handleState3Transition(StateChange stateChange) {
        //Do stuff similar to above
    }
}

public class State {

    public enum StateType {
        STATE1, STATE2, STATE3
    }

    public StateType stateType;

    //Bunch of other properties


}

事实证明这是非常程序化的。我对其进行了重构以尝试使其更加面向对象。

@ApplicationScoped
public class StateService {

    @Inject
    MailService mailSerice;

    //Inject some other stuff

    private Map<String, State> state = new HashMap<String, State>();

    public void makeStateTransition(StateChange stateChange) {
        State currentState = state.get(stateChange.getKey());
        State newState = currentState.handleStateChange(stateChange, mailService);
        state.put(stateChange.getKey(), newState);
    }
}

现在 StateService 不需要知道所有的状态转换

public abstract class State {
    //Some protected fields shared by all states

    public abstract State handleStateChange(StateChange stateChange, MailService mailService);
}

public class SomeState extends State {

    //Some properties specific to this state

    public State handleStateChange(StateChange stateChange, MailService mailSerice) {
        //Do some stuff to handle state and use injected mailsender to send some email
        mailSerice.sendEmail("Send some email");
        return new SomeOtherState();
    }
}

这会产生更好的代码，尤其是随着可能状态数量的增加。问题是让注入的邮件发件人进入需要它的正确状态。有些州可能不需要它，而另一些州可能需要别的东西。因为状态不是由容器创建的，所以它们自己不能使用注入。在状态的构造函数中传递注入的字段是可能的，但是注入的对象可能会在非托管状态中变得“陈旧”？

我求助于在方法调用中将其作为参数发送，这样它应该始终是“新鲜的”。如果需要将许多注入作为参数发送并且在某种程度上感觉错误，则非常麻烦。

您将如何建议如何处理此示例中状态对象所需的注入资源？

请忽略课堂上的任何线程问题。

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