【命令設計模式詳解】C/Java/JS/Go/Python/TS不同語言實現

刀法如飛發表於2023-03-30

簡介

命令模式(Command Pattern)是一種資料驅動的設計模式,也是一種行為型設計模式。這種模式的請求以命令的形式包裹在物件中,並傳給呼叫物件。呼叫物件再尋找合適的物件,並把該命令傳給相應的處理者。即把請求或操作封裝成單個物件,並使其可以被引數化和延遲執行,這種方式將命令和執行者進行了有效解耦。

如果你需要透過操作來引數化物件,可使用命令模式。如果你想要將操作放入佇列中、操作的執行或者遠端執行操作, 可使用命令模式。如果你想要實現操作回滾功能,可使用命令模式。

作用

  1. 將不同命令按照抽象命令封裝成不同的物件,將這些命令放到呼叫者裡。
  2. 客戶透過呼叫者執行命令再去呼叫接受者的動作,順序為:客戶呼叫方->呼叫者->命令物件->接受者。
  3. 同其他物件一樣,命令也可以實現序列化,從而方便地寫入檔案或資料庫中,實現延遲執行。

實現步驟

  1. 建立一個抽象命令介面,實現基本的命令方法。
  2. 建立多個具體命令類,實現抽象命令介面,以來命令接收者。
  3. 建立命令接收者,也就是具體業務類,接受命令並執行動作。
  4. 建立命令呼叫者,這是一個聚合命令的類,新增命令和執行命令。

UML

 

Java程式碼

基礎命令介面

// Command.java 命令抽象介面
public interface Command {
   void execute();
}

 

具體命令類,可以多個命令

// BuyCommand.java 購買命令,操作receiver,實現了抽象命令類
public class BuyCommand implements Command {
  private StockReceiver stockReceiver;

  public BuyCommand(StockReceiver stockReceiver) {
    this.stockReceiver = stockReceiver;
  }

  // 命令類呼叫執行者的實際動作
  public void execute() {
    System.out.println(this.getClass().getName() + "::execute() ");
    this.stockReceiver.buy();
  }
}
// SellCommand.java 出售命令,操作receiver,實現了抽象命令類
public class SellCommand implements Command {
  private StockReceiver stockReceiver;

  public SellCommand(StockReceiver stockReceiver) {
    this.stockReceiver = stockReceiver;
  }

  // 命令類呼叫執行者的實際動作
  public void execute() {
    System.out.println(this.getClass().getName() + "::execute() ");
    stockReceiver.sell();
  }
}

 

命令呼叫類

// CommandInvoker.java 命令呼叫類,透過關聯命令來執行命令的呼叫
public class CommandInvoker {

    private List<Command> commandList = new ArrayList<Command>();

    // 儲存命令
    public void takeOrder(Command command) {
        System.out.println(this.getClass().getName() + "::takeOrder() " + command.getClass().getName());
        commandList.add(command);
    }

    // 統一執行
    public void executeOrders() {
        System.out.println(this.getClass().getName() + "::executeOrders() ");
        for (Command command : commandList) {
            command.execute();
        }
        commandList.clear();
    }
}

 

命令接收執行類

// StockReceiver.java 命令模式真正的執行類,不直接對外,透過command來呼叫
public class StockReceiver {

   private String name;
   private int num;

   public StockReceiver(String name, int num) {
      this.name = name;
      this.num = num;
   }

   public void buy() {
      System.out.println(this.getClass().getName() + "::buy() [name=" + this.name + " num=" + this.num + "]");
   }

   public void sell() {
      System.out.println(this.getClass().getName() + "::sell() [name=" + this.name + " num=" + this.num + "]");
   }

   public void setName(String name) {
      this.setName(name);
   }

   public String getName() {
      return this.name;
   }

   public void setNum(int num) {
      this.num = num;
   }

   public int getNum() {
      return this.num;
   }
}

 

測試呼叫

    /*
     * 命令模式是客戶端透過一個命令執行者invoker,去執行某個命令command。
     * 而命令則呼叫了業務類receiver的具體動作,從而完成真正的執行。
     * 這種方式將命令和執行者進行了有效解耦。
     */

    // 先宣告一個被操作物件,也就是接收者
    StockReceiver stock1 = new StockReceiver("Apple", 200);

    // 再宣告具體的命令
    BuyCommand buyCommand = new BuyCommand(stock1);
    SellCommand sellCommand = new SellCommand(stock1);

    // 最後宣告呼叫者,由呼叫者來執行具體命令
    CommandInvoker invoker = new CommandInvoker();
    invoker.takeOrder(buyCommand);
    invoker.takeOrder(sellCommand);
    invoker.executeOrders();

    // 再執行一隻股票
    StockReceiver stock2 = new StockReceiver("Google", 100);
    BuyCommand buyCommand2 = new BuyCommand(stock2);
    invoker.takeOrder(buyCommand2);
    invoker.executeOrders();

 

Go程式碼

基礎命令介面

// Command.go 命令抽象介面
type Command interface {
  GetName() string
  SetStockReceiver(stockReceiver *StockReceiver)
  Execute()
}

 

具體命令類,可以多個命令

// BuyCommand.go 購買命令,操作receiver,實現了抽象命令類
type BuyCommand struct {
  Name          string `default:"BuyCommand"`
  stockReceiver *StockReceiver
}

func (c *BuyCommand) GetName() string {
  return c.Name
}

func (c *BuyCommand) SetStockReceiver(stockReceiver *StockReceiver) {
  c.stockReceiver = stockReceiver
}

// 命令類呼叫執行者來自行真正的動作
func (c *BuyCommand) Execute() {
  fmt.Println("BuyCommand::Execute() ")
  c.stockReceiver.Buy()
}
// SellCommand.go 出售命令,操作receiver,實現了抽象命令類
type SellCommand struct {
  Name          string `default:"BuyCommand"`
  stockReceiver *StockReceiver
}

func (s *SellCommand) GetName() string {
  return s.Name
}

func (s *SellCommand) SetStockReceiver(stockReceiver *StockReceiver) {
  s.stockReceiver = stockReceiver
}

// 命令類呼叫執行者來自行真正的動作
func (s *SellCommand) Execute() {
  fmt.Println("SellCommand::Execute() ")
  s.stockReceiver.Sell()
}

 

命令呼叫類

// CommandInvoker.go 命令呼叫類,透過關聯命令來執行命令的呼叫
type CommandInvoker struct {
  Name        string
  commandList []Command
}

func (c *CommandInvoker) GetName() string {
  return c.Name
}

// 儲存命令
func (c *CommandInvoker) TakeOrder(command Command) {
  fmt.Println("CommandInvoker::TakeOrder() " + command.GetName())
  c.commandList = append(c.commandList, command)
}

// 統一執行
func (c *CommandInvoker) ExecuteOrders() {
  fmt.Println("CommandInvoker::ExecuteOrders() ")
  for _, command := range c.commandList {
    command.Execute()
  }
  // 命令執行後清除
  c.commandList = c.commandList[:0]
}

 

命令接收執行類

// StockReceiver.go 命令模式真正的執行類,不直接對外,透過command來呼叫
type StockReceiver struct {
  Name string
  Num  int
}

func (s *StockReceiver) Buy() {
  fmt.Println("StockReceiver::Buy() [Name=" +
    s.Name + " Num=" + strconv.Itoa(s.Num) + "]")
}

func (s *StockReceiver) Sell() {
  fmt.Println("StockReceiver::Sell() [Name=" +
    s.Name + " Num=" + strconv.Itoa(s.Num) + "]")
}

 

測試呼叫

// main包下的main入口方法
func main() {
  fmt.Println("test start:")
  /*
   * 命令模式是客戶端透過一個命令執行者invoker,去執行某個命令command
   * 而命令則呼叫了業務類receiver的具體動作,從而完成真正的執行
   * 這種方式將命令和執行者進行了有效解耦。
   */

  // 先宣告一個被操作物件,也就是接收者
  var stock1 = &src.StockReceiver{
    Name: "Apple",
    Num:  200,
  }

  // 再宣告具體的命令
  var buyCommand = &src.BuyCommand{
    Name: "buyCommand",
  }
  buyCommand.SetStockReceiver(stock1)
  var sellCommand = &src.SellCommand{
    Name: "sellCommand",
  }
  sellCommand.SetStockReceiver(stock1)

  // 最後宣告呼叫者,由呼叫者來執行具體命令
  var invoker = &src.CommandInvoker{
    Name: "invoker",
  }
  invoker.TakeOrder(buyCommand)
  invoker.TakeOrder(sellCommand)
  invoker.ExecuteOrders()

  // 再執行一隻股票
  var stock2 = &src.StockReceiver{
    Name: "Google",
    Num:  100,
  }
  var buyCommand2 = &src.BuyCommand{
    Name: "buyCommand2",
  }
  buyCommand2.SetStockReceiver(stock2)
  invoker.TakeOrder(buyCommand2)
  invoker.ExecuteOrders()
}

 

C語言程式碼

基礎物件定義

// func.h檔案,基礎命令結構體head
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>

// 基礎命令結構體
typedef struct Command
{
    char name[50];
    struct StockReceiver *stock_receiver;
    void (*set_stock_receiver)(struct Command *command, struct StockReceiver *);
    void (*execute)(struct Command *);
} Command;

// 接受者物件
typedef struct StockReceiver
{
    char name[50];
    int num;
    void (*buy)(struct StockReceiver *);
    void (*sell)(struct StockReceiver *);
} StockReceiver;
StockReceiver *stock_receiver_constructor(char *name, int num);

// 繼承命令結構體
typedef struct BuyCommand
{
    char name[50];
    struct StockReceiver *stock_receiver;
    void (*set_stock_receiver)(struct BuyCommand *command, struct StockReceiver *);
    void (*execute)(struct Command *);
} BuyCommand;
BuyCommand *buy_command_constructor(char *name);

// 繼承命令結構體
typedef struct SellCommand
{
    char name[50];
    struct StockReceiver *stock_receiver;
    void (*set_stock_receiver)(struct SellCommand *command, struct StockReceiver *);
    void (*execute)(struct Command *);
} SellCommand;
SellCommand *sell_command_constructor(char *name);

// 命令執行者
typedef struct CommandInvoker
{
    char name[50];
    void (*take_order)(struct CommandInvoker *invoker, Command *command);
    void (*execute_orders)(struct CommandInvoker *invoker);
    // 陣列命令列表,記錄待執行的命令物件
    struct Command **command_list;
    // 陣列長度記錄
    int command_list_size;
    // 若是柔性陣列,則放在結構體最後,可以動態追加內容
    // struct Command *command_list[];
} CommandInvoker;
CommandInvoker *command_invoker_constructor(char *name);

 

具體命令類,可以多個命令

// buy_command.c 購買命令,操作receiver,實現了抽象命令類
#include "func.h"

// 購買命令,操作receiver,實現了抽象命令類

void set_buy_stock_receiver(BuyCommand *command, StockReceiver *receiver)
{
  command->stock_receiver = receiver;
}

// 命令類呼叫執行者來自行真正的動作
void buy_command_execute(Command *command)
{
  printf("\r\n BuyCommand::execute() [command->name=%s]", command->name);
  command->stock_receiver->buy(command->stock_receiver);
}

// 建立Buy命令物件
BuyCommand *buy_command_constructor(char *name)
{
  Command *command = (Command *)malloc(sizeof(Command));
  strncpy(command->name, name, 50);
  command->execute = &buy_command_execute;
  // 轉為BuyCommand
  BuyCommand *buy_command = (BuyCommand *)command;
  buy_command->set_stock_receiver = &set_buy_stock_receiver;
  return buy_command;
}
// sell_command.c 出售命令,操作receiver,實現了抽象命令類
#include "func.h"

// 出售命令,操作receiver,實現了抽象命令類

void set_sell_stock_receiver(SellCommand *command, StockReceiver *receiver) {
  command->stock_receiver = receiver;
}

// 命令類呼叫執行者來自行真正的動作
void sell_command_execute(Command *command) {
  printf("\r\n SellCommand::execute() [command->name=%s]", command->name);
  command->stock_receiver->sell(command->stock_receiver);
}

// 建立Sell命令物件
SellCommand *sell_command_constructor(char *name)
{
  Command *command = (Command *)malloc(sizeof(Command));
  strncpy(command->name, name, 50);
  command->execute = &sell_command_execute;
  // 轉為SellCommand
  SellCommand *buy_command = (SellCommand *)command;
  buy_command->set_stock_receiver = &set_sell_stock_receiver;
  return buy_command;
}

 

命令呼叫類

// command_invoker.c 命令呼叫類,透過關聯命令來執行命令的呼叫
#include "func.h"

/*
命令呼叫類,透過關聯命令來實行命令的呼叫
在命令模式中,Invoker(呼叫者)是一個可選的元件,
它負責將Command物件傳遞給Receiver,
並呼叫Command物件的execute方法來執行命令。
Invoker在實現命令模式時可以有多種實現方式。
*/

void print_command_list(Command **list, int command_list_size)
{
  printf("\r\nThe current command_list:");
  for (int i = 0; i < command_list_size; i++)
  {
    printf("\r\n [i=%d, command->name=%s]", i, list[i]->name);
  }
}

// 把命令儲存到呼叫者的命令列表
void invoker_take_order(CommandInvoker *invoker, Command *command)
{
  printf("\r\n CommandInvoker::take_order() [invoker->name=%s, command->name=%s, invoker->command_list_size=%d]", invoker->name, command->name, invoker->command_list_size);

  // 列表長度增加1位
  int new_command_list_size = invoker->command_list_size + 1;

  /* 如果採取柔性陣列,則無需申請新空間和複製內容 */
  // 把原列表命令暫存下來
  Command **old_command_list = invoker->command_list;
  // 給命令列表申請新空間
  invoker->command_list = (Command **)calloc(new_command_list_size, sizeof(Command *));
  // 複製原有命令到命令列表,如果採取柔性陣列則無需複製
  for (int i = 0; i < invoker->command_list_size; i++)
  {
    invoker->command_list[i] = old_command_list[i];
  }
  free(old_command_list);

  // 把新的命令新增列表最後
  invoker->command_list[new_command_list_size - 1] = command;
  invoker->command_list_size = new_command_list_size;
  
  // 列印當前有多少命令
  // print_command_list(invoker->command_list, invoker->command_list_size);
}

// 統一執行全部命令
void invoker_execute_orders(CommandInvoker *invoker)
{
  printf("\r\n CommandInvoker::execute_orders() ");
  int command_list_size = invoker->command_list_size;
  Command **command_list = invoker->command_list;
  for (int i = 0; i < command_list_size; i++)
  {
    Command *command = command_list[i];
    command->execute(command);
    command_list[i] = NULL;
  }
  // 命令執行完後清除命令列表
  invoker->command_list_size = 0;
  invoker->command_list = (Command **)calloc(0, sizeof(Command *));
}

// 初始化CommandInvoker命令物件
CommandInvoker *command_invoker_constructor(char *name)
{
  printf("\r\n command_invoker_constructor() [name=%s]", name);
  CommandInvoker *invoker = (CommandInvoker *)malloc(sizeof(CommandInvoker));
  strncpy(invoker->name, name, 50);
  invoker->command_list_size = 0;
  invoker->take_order = &invoker_take_order;
  invoker->execute_orders = &invoker_execute_orders;
  return invoker;
}

 

命令接收執行類

// stock_receiver.c 命令模式真正的執行類,不直接對外,透過command來呼叫
#include "func.h"

/* 命令模式真正的執行類,不直接對外,透過command來呼叫 */

void stock_receiver_buy(StockReceiver *stock_receiver) {
  printf("\r\n StockReceiver::buy() [name=%s num=%d]", stock_receiver->name, stock_receiver->num);
}

void stock_receiver_sell(StockReceiver *stock_receiver) {
  printf("\r\n StockReceiver::sell() [name=%s num=%d]", stock_receiver->name, stock_receiver->num);
}

// 建立StockReceiver命令物件
StockReceiver *stock_receiver_constructor(char *name, int num)
{
  printf("\r\n stock_receiver_constructor() [name=%s, num=%d]", name, num);
  StockReceiver *receiver = (StockReceiver *)malloc(sizeof(StockReceiver));
  strncpy(receiver->name, name, 50);
  receiver->num = num;
  receiver->buy = &stock_receiver_buy;
  receiver->sell = &stock_receiver_sell;
  return receiver;
}

 

測試呼叫

#include "../src/func.h"

int main(void)
{
    printf("test start:\r\n");
    /*
     * 命令模式是一種行為設計模式,它將請求或操作封裝成單個物件,並使其可以被引數化和延遲執行。
     * 在命令模式中,客戶端透過一個命令執行者invoker,去執行某個命令command
     * 而命令則呼叫了業務類receiver的具體動作,從而完成真正的執行
     * 這種方式將命令和執行者進行了有效解耦。
     */

    // 先宣告一個被操作物件,也就是接收者
    StockReceiver *stocker_receiver1 = stock_receiver_constructor("Apple", 200);

    // 再宣告具體的命令
    BuyCommand *buy_command = buy_command_constructor("buy_command");
    buy_command->set_stock_receiver(buy_command, stocker_receiver1);

    SellCommand *sell_command = sell_command_constructor("sell_command");
    sell_command->set_stock_receiver(sell_command, stocker_receiver1);

    // 最後宣告呼叫者,由呼叫者來執行具體命令
    CommandInvoker *invoker = command_invoker_constructor("invoker");
    invoker->take_order(invoker, (Command *)buy_command);
    invoker->take_order(invoker, (Command *)sell_command);
    invoker->execute_orders(invoker);

    // 再執行一隻股票,宣告新的接受者
    StockReceiver *stock_receiver2 = stock_receiver_constructor("Google", 100);
    BuyCommand *buy_command2 = buy_command_constructor("buy_command2");
    // 這次只有buy命令
    buy_command2->set_stock_receiver(buy_command2, stock_receiver2);
    // 還用原來的invoker,或者新建invoker
    invoker->take_order(invoker, (Command *)buy_command2);
    invoker->execute_orders(invoker);

    return 0;
}

 

更多語言版本

不同語言實現設計模式原始碼:https://github.com/microwind/design-pattern

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