精通Java设计模式从初见到相爱之命令设计模式(15)

1、概念

    请求以命令的形式包裹在对象中，并传给调用对象。调用对象寻找可以处理该命令的合适的对象，并把该命令传给相应的对象，该对象执行命令。

2、场景

    2.1 ：工作流Activit框架中就用到了这种模式，它总共7个接口，每个接口都有特定的命令去执行数据库中的表，因为activit框架会自动生成23张表，所以这些命令都会在这些表中直接增删改查，我们在后台直接调用这些命令就好。

3、简单代码实现

    

public interface Order {

    void execute();
}

public class Apple {

    private String name = "ABC";
    private int quantity = 10;

    public void buy(){
        System.out.println("买家name="+name+" quantity="+quantity);
    }
    public void sell(){
        System.out.println("卖家name="+name+" quantity="+quantity);
    }
}

public class BuyApple implements Order {

    private Apple apple;

    public BuyApple(Apple apple) {
        this.apple = apple;
    }

    @Override
    public void execute() {
        apple.buy();
    }
}

public class SellApple implements Order {

    private Apple apple;

    public SellApple(Apple apple){
        this.apple = apple;
    }

    @Override
    public void execute() {
        apple.sell();
    }
}

public class Command {

    private List<Order> orderList = new ArrayList<>();

    public void takeOrder(Order order){
        orderList.add(order);
    }

    public void placeOrders(){
        for (Order order : orderList) {
            order.execute();
        }
        orderList.clear();
    }
}

main函数执行结果

public class Main {
    public static void main(String[] args) {
        Apple apple = new Apple();

        BuyApple buyStockOrder = new BuyApple(apple);
        SellApple sellStockOrder = new SellApple(apple);

        Command command = new Command();
        command.takeOrder(buyStockOrder);
        command.takeOrder(sellStockOrder);

        command.placeOrders();
    }
}