命令模式

命令模式（Command Pattern）是一种数据驱动的设计模式，它属于行为型模式。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。

示例演示：

1. 我们创建一个people实体，并提供两个方法

   package test.command;
   
   public class People {
   
       private Integer id = 1;
       private String name = "1";
   
       public void add() {
           System.out.println("add id: " + id + " name:" + name);
       }
   
       public void remove() {
           System.out.println("remove id: " + id + " name:" + name);
       }
   }

2. 新建一个order命令的接口

   package test.command;
   
   public interface Order {
       void execute();
   }

3. 分别对people的add和remove方法创建order接口的实体类

   package test.command;
   
   public class PeopleAdd implements Order {
       private People people;
   
       public PeopleAdd(People people) {
           this.people = people;
       }
   
       @Override
       public void execute() {
           people.add();
       }
   }

   package test.command;
   
   public class PeopleRemove implements Order {
       private People people;
   
       public PeopleRemove(People people) {
           this.people = people;
       }
   
       @Override
       public void execute() {
           people.remove();
       }
   }

4. 创建一个命令调用实体类

   package test.command;
   
   import java.util.ArrayList;
   import java.util.List;
   
   public class Broker {
       private List<Order> orders = new ArrayList<>();
   
       public void takeOrder(Order order) {
           orders.add(order);
       }
   
       public void placeOrders() {
           for (Order order : orders) {
               order.execute();
           }
           orders.clear();
       }
   }

5. 完成上述步骤，我们就可以开始演示了

   package test.command;
   
   public class CommandDemo {
       public static void main(String[] args) {
           People people = new People();
           PeopleAdd peopleAdd = new PeopleAdd(people);
           PeopleRemove peopleRemove = new PeopleRemove(people);
   
           Broker broker = new Broker();
           broker.takeOrder(peopleAdd);
           broker.takeOrder(peopleRemove);
           broker.placeOrders();
       }
   }

   运行结果：

   add id: 1name:1
   remove id: 1name:1

说明：

优点： 1、降低了系统耦合度。 2、新的命令可以很容易添加到系统中去。

缺点：使用命令模式可能会导致某些系统有过多的具体命令类。