命令模式（请求与具体实现解耦）

目录

前言

UML

plantuml

类图

实战代码

模板

Command

Invoker

Receiver

Client

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前言

命令模式解耦了命令请求者（Invoker）和命令执行者（receiver），使得 Invoker 不再直接引用 receiver，而是依赖于抽象的命令接口。具体的命令类则直接引用 receiver，通过调用 receiver 的方法来执行命令。

解耦之后，具体命令的增删改不再影响 Invoker，同时，抽象出来的命令请求还能队列化，从而实现撤销和重试功能，或做排列组合合成复杂的命令。

在 Invoker 中，也体现了桥接模式的思想，将命令的抽象和具体的实现分离，使 Invoker 中命令的添加和扩展更加简单。不过具体的命令类并不直接实现处理逻辑，而是交给了 receiver 来实现，这也是命令模式和桥接模式最主要的区别。

UML plantuml @startuml 'https://plantuml.com/class-diagram interface Command { + execute() : void } class CommandA { - receiver : Receiver + CommandA(Receiver) + execute() : void } class CommandB { - receiver : Receiver + CommandB(Receiver) + execute() : void } class Receiver { + executeA() : void + executeB() : void } class Invoker { - commands : List<Command> + addCommand(Command) : void + execute(Command) : void + executes() : void } class Client {} Command <|.. CommandA Command <|.. CommandB CommandA "1" --> "1" Receiver CommandB "1" --> "1" Receiver Invoker "1" --> "n" Command Client ..> Invoker Client ..> Command @enduml 类图

实战代码 模板 Command public interface Command { void execute(); } public class ConcreteCommand1 implements Command { private Receiver receiver; public ConcreteCommand1(Receiver receiver) { this.receiver = receiver; } public void execute() { receiver.execute1(); } } public class ConcreteCommand2 implements Command { private Receiver receiver; public ConcreteCommand2(Receiver receiver) { this.receiver = receiver; } public void execute() { receiver.execute2(); } } Invoker public class Invoker { private List<Command> commands = new ArrayList<Command>(); public void addCommand(Command command){ commands.add(command); } public void execute(Command command){ command.execute(); } public void executes(){ for(Command command : commands){ command.execute(); } commands.clear(); } } Receiver public class Receiver { public void execute1() { System.out.println("execute1."); } public void execute2() { System.out.println("execute2."); } } Client public class Test { public static void main(String[] args) { Receiver receiver = new Receiver(); Invoker invoker = new Invoker(); invoker.execute(new Command1(receiver)); invoker.addAction(new Command1(receiver)); invoker.addAction(new Command2(receiver)); invoker.executes(); } }