Java设计模式之状态模式

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1、解决的问题

订单的状态变化，待支付、待发货、待签收、已取消、已完成，待支付和待发货状态下可以进行支付和取消两个动作。

正常写法：

        String action = "payOrder";        OrderStateEnum state = OrderStateEnum.WaitPay;        if (OrderStateEnum.WaitPay.equals(state)) {            if ("payOrder".equals(action)) {                System.out.println("支付订单，修改成待发货状态");                state = OrderStateEnum.WaitDeliver;            }            if ("cancel".equals(action)) {                System.out.println("取消订单，修改成已取消");                state = OrderStateEnum.Cancel;            }        }        else if(OrderStateEnum.WaitDeliver.equals(state)) {            if ("deliverOrder".equals(action)) {                System.out.println("订单发货，修改成待签收状态");                state = OrderStateEnum.WaitSign;            }            if ("cancel".equals(action)) {                System.out.println("取消订单，修改成已取消");                state = OrderStateEnum.Cancel;            }        }        //其他判断的省略        System.out.println("最终的订单状态：" + state.getName());

这种写法如果进行状态的增加，代码会非常复杂，可读性差

2、使用状态模式：

public enum OrderStateEnum {    /**待支付*/    WaitPay("待支付"),    /**待发货*/    WaitDeliver("待发货"),    /**待签收*/    WaitSign("待签收"),    /**已完成*/    Finish("已完成"),    /**已取消*/    Cancel("已取消");    private String name;    OrderStateEnum(String name) {        this.name = name;    }    public String getName() {        return name;    }}

public abstract class OrderState {    private OrderStateContext context;    public void setContext(OrderStateContext context) {        this.context = context;    }    public OrderStateContext getContext() {        return context;    }    /**     * 支付订单     */    public abstract void payOrder();    /**     * 订单发货     */    public abstract void deliverOrder();    /**     * 用户确认收货     */    public abstract void signOrder();    /**     * 取消订单     */    public abstract void cancelOrder();    public abstract OrderStateEnum getCurrentState();}

public class OrderStateContext {    //定义出所有的订单状态    public static OrderState waitPayState;    public static OrderState waitDeliverState;    public static OrderState waitSignState;    public static OrderState cancelState;    public static OrderState finishState;    public OrderStateContext(String orderId) {        waitPayState = new WaitPayState(orderId);        waitDeliverState = new WaitDeliverState(orderId);        waitSignState = new WaitSignState(orderId);        cancelState = new CancelState(orderId);        finishState = new FinishState(orderId);    }    /**     * 当前状态     */    private OrderState state;    public OrderState getState() {        return state;    }    public void setState(OrderState state) {        this.state = state;        //把当前的环境通知到各个实现类中        this.state.setContext(this);    }    public void payOrder() {        this.state.payOrder();    }    public void deliverOrder() {        this.state.deliverOrder();    }    public void signOrder() {        this.state.signOrder();    }    public void cancelOrder() {        this.state.cancelOrder();    }}

/** * 在订单待发货的状态下能做什么事情 */public class WaitDeliverState extends OrderState {    private String orderId;    public WaitDeliverState(String orderId) {        this.orderId = orderId;    }    @Override    public void payOrder() {    }    @Override    public void deliverOrder() {        System.out.println("订单" + orderId + "发货");        this.getContext().setState(OrderStateContext.waitSignState);    }    @Override    public void signOrder() {    }    @Override    public void cancelOrder() {        //状态修改        this.getContext().setState(OrderStateContext.cancelState);        //动作委托为cancelState来执行，最终状态        this.getContext().getState().cancelOrder();    }    @Override    public OrderStateEnum getCurrentState() {        return OrderStateEnum.WaitDeliver;    }}

/** * 在订单未支付的状态下能做什么事情 */public class WaitPayState extends OrderState {    private String orderId;    public WaitPayState(String orderId) {        this.orderId = orderId;    }    @Override    public void payOrder() {        //变更状态前，要执行的事件，或者检查条件        System.out.println("支付" + orderId + "订单");        //状态修改        this.getContext().setState(OrderStateContext.waitDeliverState);    }    @Override    public void deliverOrder() {    }    @Override    public void signOrder() {    }    @Override    public void cancelOrder() {        //状态修改        this.getContext().setState(OrderStateContext.cancelState);        //动作委托为cancelState来执行，最终状态        this.getContext().getState().cancelOrder();    }    @Override    public OrderStateEnum getCurrentState() {        return OrderStateEnum.WaitPay;    }}

public class CancelState extends OrderState {    private String orderId;    public CancelState(String orderId) {        this.orderId = orderId;    }    @Override    public void payOrder() {    }    @Override    public void deliverOrder() {    }    @Override    public void signOrder() {    }    @Override    public void cancelOrder() {        System.out.println("取消" + orderId + "订单");    }    @Override    public OrderStateEnum getCurrentState() {        return OrderStateEnum.Cancel;    }}

3、运行效果

public static void main(String[] args) {        OrderStateContext context = new OrderStateContext("11132");        context.setState(OrderStateContext.waitPayState);//初始状态        context.payOrder();//订单支付        System.out.println("订单状态为：" + context.getState().getCurrentState().getName());        context.deliverOrder();//发货        System.out.println("订单状态为：" + context.getState().getCurrentState().getName());        context.cancelOrder();//取消订单        System.out.println("订单状态为：" + context.getState().getCurrentState().getName());    }

支付11132订单订单状态为：待发货订单11132发货订单状态为：待签收取消11132订单订单状态为：已取消

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