设计模式之命令模式

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设计模式之命令模式

第一个命令对象

实现命令接口

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/**
 * 命令接口
 * @author Mr.zxb
 * @date 2020-08-16 20:42:17
 */
public interface Command {
    /**
     * 执行命令接口
     */
    void execute();
}

实现一个打开电灯的命令

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/**
 * 电灯类
 * @author Mr.zxb
 * @date 2020-08-16 20:44:01
 */
public class Light {

    public void on() {
        System.out.println("Light is on");
    }

    public void off() {
        System.out.println("Light is off");
    }
}z
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/**
 * 打开电灯的命令
 * @author Mr.zxb
 * @date 2020-08-16 20:43:31
 */
public class LightOnCommand implements Command {

    private Light light;

    public LightOnCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.on();
    }
}

创建一个简单遥控器

设计一个遥控器对象，它只有一个按钮和对应的插槽，可以控制一个简单装置

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/**
 * 简单的遥控器
 * @author Mr.zxb
 * @date 2020-08-16 20:47:25
 */
public class SimpleRemoteControl {
    /**
     * 一个插槽
     */
    private Command slot;

    /**
     * 设置插槽控制的命令
     * @param command
     */
    public void setCommand(Command command) {
        slot = command;
    }

    /**
     * 按下按钮的功能
     */
    public void buttonWasPressed() {
        slot.execute();
    }
}

遥控器使用的简单测试

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/**
 * 遥控器简单测试
 * @author Mr.zxb
 * @date 2020-08-16 20:49:47
 */
public class RemoteControlTest {
    public static void main(String[] args) {
        // 实例化一个简单遥控器装置
        SimpleRemoteControl remote = new SimpleRemoteControl();
        // 创建一个电灯
        Light light = new Light();
        // 创建一个命令
        LightOnCommand lightOnCommand = new LightOnCommand(light);

        // 把命令传给调用者
        remote.setCommand(lightOnCommand);
        // 执行命令
        remote.buttonWasPressed();
    }
}

定义命令模式

命令模式将“请求”封装成对象，以便使用不同的请求、队列或者日志来参数化其他对象。命令模式也支持可撤销的操作。

定义命令模式类图

实现一个复杂遥控器

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/**
 * 遥控器
 * @author Mr.zxb
 * @date 2020-08-16 20:59:49
 */
public class RemoteControl {
    /**
     * 一组打开命令
     */
    private final Command[] onCommands;
    /**
     * 一组关闭命令
     */
    private final Command[] offCommands;
    /**
     * 撤销命令
     */
    private Command undoCommand;

    public RemoteControl() {
        this.onCommands = new Command[7];
        this.offCommands = new Command[7];

        // 预先设置无命令的Command
        Command noCommand = new NoCommand();
        for (int i = 0; i < 7; i++) {
            this.onCommands[i] = noCommand;
            this.offCommands[i] = noCommand;
        }
        this.undoCommand = noCommand;
    }

    /**
     * 指定插槽设置开和关命令
     * @param slot
     * @param onCommand
     * @param offCommand
     */
    public void setCommand(int slot, Command onCommand, Command offCommand) {
        this.onCommands[slot] = onCommand;
        this.offCommands[slot] = offCommand;
    }

    public void onButtonWasPushed(int slot) {
        this.onCommands[slot].execute();
        this.undoCommand = onCommands[slot];
    }

    public void offButtonWasPushed(int slot) {
        this.offCommands[slot].execute();
        this.undoCommand = offCommands[slot];
    }

    public void undoButtonWasPushed() {
        this.undoCommand.undo();
    }

    @Override
    public String toString() {
        StringBuffer buffer = new StringBuffer();
        buffer.append("\n------- Remote Control-------\n");
        for (int i = 0; i < this.onCommands.length; i++) {
            buffer.append("[slot ")
                    .append(i)
                    .append(" ]")
                    .append(this.onCommands[i].getClass().getName())
                    .append("    ")
                    .append(this.offCommands[i].getClass().getName())
                    .append("\n");
        }
        return buffer.toString();
    }
}

实现其他命令

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/**
 * 打开电灯的命令
 * @author Mr.zxb
 * @date 2020-08-16 20:43:31
 */
public class LightOnCommand implements Command {

    private Light light;

    public LightOnCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.on();
    }

    @Override
    public void undo() {
        light.off();
    }
}

/**
 * 关闭电灯的命令
 * @author Mr.zxb
 * @date 2020-08-16 20:43:31
 */
public class LightOffCommand implements Command {

    private Light light;

    public LightOffCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.off();
    }

    @Override
    public void undo() {
        light.on();
    }
}

/**
 * 音响类
 * @author Mr.zxb
 * @date 2020-08-16 21:09:29
 */
public class Stereo {
    
    private String name;
    
    public Stereo(String name) {
        this.name = name;
    }

    public void on() {
        System.out.printf("%s stereo is on\n", name);
    }

    public void off() {
        System.out.printf("%s stereo is off\n", name);
    }

    public void setCD() {
        System.out.printf("%s stereo is et for CD input\n", name);
    }

    public void setVolume(int volume) {
        System.out.printf("%s stereo volume se to 11\n", name);
    }
}

/**
 * 音响命令对象
 * @author Mr.zxb
 * @date 2020-08-16 21:09:13
 */
public class StereoOnWithCDCommand implements Command {

    private Stereo stereo;

    public StereoOnWithCDCommand(Stereo stereo) {
        this.stereo = stereo;
    }

    @Override
    public void execute() {
        stereo.on();
        stereo.setCD();
        stereo.setVolume(11);
    }

    @Override
    public void undo() {
        stereo.off();
    }
}

/**
 * 音响命令对象
 * @author Mr.zxb
 * @date 2020-08-16 21:09:13
 */
public class StereoOffWithCDCommand implements Command {

    private Stereo stereo;

    public StereoOffWithCDCommand(Stereo stereo) {
        this.stereo = stereo;
    }

    @Override
    public void execute() {
        stereo.off();
    }

    @Override
    public void undo() {
        stereo.on();
    }
}

测试我们的遥控器

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public class RemoteLoader {
    public static void main(String[] args) {
        RemoteControl remoteControl = new RemoteControl();

        // 将所有装置创建在合适的位置
        Light livingRoomLight = new Light("Living Room");
        Light kitchenLight = new Light("Kitchen");
        Stereo stereo = new Stereo("Living Room");

        // 创建所有电灯命令对象
        LightOnCommand livingRoomLightOn = new LightOnCommand(livingRoomLight);
        LightOnCommand kitchenLightLightOn = new LightOnCommand(kitchenLight);
        LightOffCommand livingRoomLightOff = new LightOffCommand(livingRoomLight);
        LightOffCommand kitchenLightLightOff = new LightOffCommand(kitchenLight);

        // 创建音响的开与关命令
        StereoOnWithCDCommand stereoOnWithCD = new StereoOnWithCDCommand(stereo);
        StereoOffWithCDCommand stereoOffWithCD = new StereoOffWithCDCommand(stereo);

        // 将各命令装置在指定的插槽
        remoteControl.setCommand(0, livingRoomLightOn, livingRoomLightOff);
        remoteControl.setCommand(1, kitchenLightLightOn, kitchenLightLightOff);
        remoteControl.setCommand(2, stereoOnWithCD, stereoOffWithCD);
        System.out.println(remoteControl);

        // 执行遥控器的按钮
        remoteControl.onButtonWasPushed(0);
        remoteControl.offButtonWasPushed(0);
        remoteControl.undoButtonWasPushed();

        remoteControl.onButtonWasPushed(1);
        remoteControl.offButtonWasPushed(1);
        remoteControl.undoButtonWasPushed();

        remoteControl.onButtonWasPushed(2);
        remoteControl.offButtonWasPushed(2);
        remoteControl.undoButtonWasPushed();
    }
}

使用宏命令

每个遥控器都应该具备“Party模式”

  • 先创建想要进入宏的命令集合：
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// 创建所有的装置，电灯、电视、音响和热水器
Light light = new Light("Living Room");
TV tv = new TV("Living Room");
Stereo stereo = new Stereo("Living Room");
Hottub hottub = new Hottub();
// 创建所有的On来控制它们
LightOnCommand lightOn = new LightOnCommand(light);
StereoOnCommand sterenOn = new StereoOnCommand(stereo);
TVOnCommand tvOn = new TVOnCommand(tv);
HottubOnCommand hottubOn = new HottubOnCommand(hottub);

// 创建所有的off来控制它们
LightOffCommand lightOff = new LightOffCommand(light);
StereoOffCommand sterenOff = new StereoOffCommand(stereo);
TVOffCommand tvOff = new TVOnCffmmand(tv);
HottubOffCommand hottubOff = new HottubOnCffmmand(hottub);
  • 接下来创建两个数组，其中记录开启命令，另一个记录关闭命令，并在数组内放入对应的命令
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/**
 * 宏命令，一组命令
 * @author Mr.zxb
 * @date 2020-08-16 21:45:21
*/
public class MacroCommand implements Command {

    private final Command[] commands;

    public MacroCommand(Command[] commands) {
        this.commands = commands;
    }

    @Override
    public void execute() {
        for (Command command : commands) {
            command.execute();
        }
    }

    @Override
    public void undo() {
        for (Command command : commands) {
            command.undo();
        }
    }
}
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// 数组用来记录开启命令，另一个数组用来记录关闭命令
Command[] partyOn = { lightOn, stereoOn, tvOn, hottubOn };
Command[] partyOff = { lightOff, sterenOff, tvOff, hottubOff };

// 创建对应的宏持有它们
MacroCommand partyOnMacro = new MacroCommand(partyOn);
MacroCommand partyOffMacro = new MacroCommand(partyOff);
  • 然后将宏命令指定给我们所希望的按钮：
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// 将宏命令指定给一个按钮
remoteControl.setCommand(4, partyOnMacro, partyOffMacro);
  • 最后，只需按下一些按钮，测试即可
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System.out.println(remoteControl);
System.out.println("--- Pushing Macro On ---");
remoteControl.onButtonWasPushed(4);
System.out.println("--- Pushing Macro Off ---");
remoteControl.offButtonWasPushed(4);

总结

  1. 命令模式将发出请求的对象和执行请求的对象解耦
  2. 在被解耦的两者之间是通过命令对象进行沟通的。命令对象封装了接收者和一个或一组动作
  3. 调用者通过命令对象的execute()发出请求，这会使得接收者的动作被调用
  4. 调用者可以接受命令当做参数，甚至在运行时动态地进行
  5. 命令可以支持撤销，做法是实现一个undo()方法来回到execute()被执行的状态
  6. 宏命令是命令的一种简单的延伸，允许调用多个命令。宏方法也可以支持撤销
  7. 实际操作时，很常见使用“聪明”命令对象，也就是直接实现了请求，而不是将工作委托给接收者
  8. 命令也可以用来实习日志和事务系统