一、介绍:
1、定义:命令模式(Command Pattern)是一种行为设计模式,它将请求封装为一个对象,从而使你可以使用不同的请求对客户端进行参数化。命令模式还支持请求的排队、记录日志、撤销操作等功能。
2、组成结构:
(1)命令接口(Command):定义执行命令的方法,可以是抽象类或接口。
public interface Command {void execute();
}
(2)具体命令类(Concrete Command):实现命令接口,封装了具体的请求和接收者,负责执行请求。
/*** 具体的命令实现*/
public class ConcreteCommand implements Command {/*** 持有相应的接收者对象*/private Receiver receiver = null;/*** 构造方法,传入相应的接收者对象* * @param receiver 相应的接收者对象*/public ConcreteCommand(Receiver receiver) {this.receiver = receiver;}/*** 执行命令*/@Overridepublic void execute() {// 通常会转调接收者对象的相应方法,让接收者来真正执行功能receiver.action();}}
(3)接收者类(Receiver):命令接受者对象,定义了命令接受者可以做的事情。执行实际的操作,命令对象将请求委托给接收者来执行。
public class Receiver {public void action() {System.out.println("执行具体操作");}
}
(4)调用者类(Invoker):Invoker类是具体命令的接收者,用于接收客户的所有命令,然后将命令转达给执行者,执行这些命令。
public class Invoker {private Command command;public void setCommand(Command command) {this.command = command;}public void executeCommand() {command.execute();}
}
客户端(Client):创建具体的命令对象,并将其分配给调用者来执行。
public class Client {public static void main(String[] args) {// 创建接收者Receiver receiver = new Receiver();// 创建命令对象,设定它的接收者Command command = new ConcreteCommand(receiver);// 创建调用者,把命令对象设置进去Invoker invoker = new Invoker();invoker.setCommand(command);// 调用者调用命令invoker.executeCommand();}
}
3、优点
- 能够比较容易的设计一个命令队列
- 在需要的情况下,可以比较容易地将命令记入日志
- 允许接收请求的一方决定是否要解决请求
- 可以容易的实现对请求的撤销和重做
- 容易扩展新的命令类
- 能够把请求一个操作的对象,与知道怎么执行一个操作的对象分隔开
二、demo:
1、点餐:服务员充当命令委托角色,在顾客和厨师之间松耦合
(1)命令:
//顾客抽象命令
public abstract class Command {public Integer count;public Integer getCount() {return count;}public void setCount(Integer count) {this.count = count;}protected Cook receiver;public Command(Cook receiver,int count) {this.receiver = receiver;this.count = count;}public abstract void execute();
}//具体命令1
public class BakeBeefCommand extends Command {public BakeBeefCommand(Cook receiver,int count) {super(receiver,count);}@Overridepublic void execute() {receiver.bakeBeef();}
}//具体命令2
public class BakeMuttonCommand extends Command{public BakeMuttonCommand(Cook receiver,int count) {super(receiver,count);}@Overridepublic void execute() {receiver.bakeMutton();}
}
(2)命令实际接收者 厨师
public class Cook {public void bakeMutton(){System.out.println("烤羊肉");}public void bakeBeef(){System.out.println("烤牛肉");}
}
(3)命令中转 服务员
public class Waiter {private List<Command> orders= new ArrayList<>();public void setOrder(Command command) {if(command.getCount() < 5){System.err.println("点餐失败,一份数量最小为5,count="+command.getCount());}else{System.out.println("点餐成功,记录日志,count="+command.getCount());this.orders.add(command);}}public void cancleOrder(Command command) {System.out.println("取消成功,记录日志,count="+command.getCount());this.orders.remove(command);}public void executeCommand(){System.out.println("***点餐结束***");for (Command comm : orders) {comm.execute();}}
}
客户端
public static void main(String[] args) {Cook receiver = new Cook();Waiter waiter = new Waiter();Command muttonCommand = new BakeMuttonCommand(receiver,1);waiter.setOrder(muttonCommand);muttonCommand = new BakeMuttonCommand(receiver,5);waiter.setOrder(muttonCommand);Command beefCommand = new BakeBeefCommand(receiver,6);waiter.setOrder(beefCommand);beefCommand = new BakeBeefCommand(receiver,7);waiter.setOrder(beefCommand);//临时取消waiter.cancleOrder(beefCommand);//全部点餐结束后执行waiter.executeCommand();}输出:
点餐失败,一份数量最小为5,count=1
点餐成功,记录日志,count=5
点餐成功,记录日志,count=6
点餐成功,记录日志,count=7
取消成功,记录日志,count=7
***点餐结束***
烤羊肉
烤牛肉