【命令设计模式详解】C/Java/JS/Go/Python/TS不同语言实现
简介
命令模式（Command Pattern）是一种数据驱动的设计模式，也是一种行为型设计模式。这种模式的请求以命令的形式包裹在对象中，并传给调用对象。调用对象再寻找合适的对象，并把该命令传给相应的处理者。即把请求或操作封装成单个对象，并使其可以被参数化和延迟执行，这种方式将命令和执行者进行了有效解耦。
如果你需要通过操作来参数化对象，可使用命令模式。如果你想要将操作放入队列中、操作的执行或者远程执行操作， 可使用命令模式。如果你想要实现操作回滚功能，可使用命令模式。
作用
- 将不同命令按照抽象命令封装成不同的对象，将这些命令放到调用者里。
- 客户通过调用者执行命令再去调用接受者的动作，顺序为：客户调用方->调用者->命令对象->接受者。
- 同其他对象一样，命令也可以实现序列化，从而方便地写入文件或数据库中，实现延迟执行。
实现步骤
- 创建一个抽象命令接口，实现基本的命令方法。
- 创建多个具体命令类，实现抽象命令接口，以来命令接收者。
- 创建命令接收者，也就是具体业务类，接受命令并执行动作。
- 创建命令调用者，这是一个聚合命令的类，添加命令和执行命令。
UML
Java代码
基础命令接口
//Command.java 命令抽象接口 public interfaceCommand {voidexecute();
}
具体命令类，可以多个命令
//BuyCommand.java 购买命令，操作receiver，实现了抽象命令类 public class BuyCommand implementsCommand {privateStockReceiver stockReceiver;publicBuyCommand(StockReceiver stockReceiver) {this.stockReceiver =stockReceiver;
}//命令类调用执行者的实际动作 public voidexecute() {
System.out.println(this.getClass().getName() + "::execute() ");this.stockReceiver.buy();
}
}//SellCommand.java 出售命令，操作receiver，实现了抽象命令类 public class SellCommand implementsCommand {privateStockReceiver stockReceiver;publicSellCommand(StockReceiver stockReceiver) {this.stockReceiver =stockReceiver;
}//命令类调用执行者的实际动作 public voidexecute() {
System.out.println(this.getClass().getName() + "::execute() ");
stockReceiver.sell();
}
}
命令调用类
//CommandInvoker.java 命令调用类，通过关联命令来执行命令的调用 public classCommandInvoker {private List<Command> commandList = new ArrayList<Command>();//储存命令 public voidtakeOrder(Command command) {
System.out.println(this.getClass().getName() + "::takeOrder() " +command.getClass().getName());
commandList.add(command);
}//统一执行 public voidexecuteOrders() {
System.out.println(this.getClass().getName() + "::executeOrders() ");for(Command command : commandList) {
command.execute();
}
commandList.clear();
}
}
命令接收执行类
//StockReceiver.java 命令模式真正的执行类，不直接对外，通过command来调用 public classStockReceiver {privateString name;private intnum;public StockReceiver(String name, intnum) {this.name =name;this.num =num;
}public voidbuy() {
System.out.println(this.getClass().getName() + "::buy() [name=" + this.name + " num=" + this.num + "]");
}public voidsell() {
System.out.println(this.getClass().getName() + "::sell() [name=" + this.name + " num=" + this.num + "]");
}public voidsetName(String name) {this.setName(name);
}publicString getName() {return this.name;
}public void setNum(intnum) {this.num =num;
}public intgetNum() {return this.num;
}
}
测试调用
/** 命令模式是客户端通过一个命令执行者invoker，去执行某个命令command。
* 而命令则调用了业务类receiver的具体动作，从而完成真正的执行。
* 这种方式将命令和执行者进行了有效解耦。*/ //先声明一个被操作对象，也就是接收者 StockReceiver stock1 = new StockReceiver("Apple", 200);//再声明具体的命令 BuyCommand buyCommand = newBuyCommand(stock1);
SellCommand sellCommand= newSellCommand(stock1);//最后声明调用者，由调用者来执行具体命令 CommandInvoker invoker = newCommandInvoker();
invoker.takeOrder(buyCommand);
invoker.takeOrder(sellCommand);
invoker.executeOrders();//再执行一只股票 StockReceiver stock2 = new StockReceiver("Google", 100);
BuyCommand buyCommand2= newBuyCommand(stock2);
invoker.takeOrder(buyCommand2);
invoker.executeOrders();
Go代码
基础命令接口
//Command.go 命令抽象接口 type Command interface{
GetName()stringSetStockReceiver(stockReceiver*StockReceiver)
Execute()
}
具体命令类，可以多个命令
//BuyCommand.go 购买命令，操作receiver，实现了抽象命令类 type BuyCommand struct{
Namestring `default:"BuyCommand"`
stockReceiver*StockReceiver
}func (c *BuyCommand) GetName() string{returnc.Name
}func (c *BuyCommand) SetStockReceiver(stockReceiver *StockReceiver) {
c.stockReceiver=stockReceiver
}//命令类调用执行者来自行真正的动作 func (c *BuyCommand) Execute() {
fmt.Println("BuyCommand::Execute()")
c.stockReceiver.Buy()
}//SellCommand.go 出售命令，操作receiver，实现了抽象命令类 type SellCommand struct{
Namestring `default:"BuyCommand"`
stockReceiver*StockReceiver
}func (s *SellCommand) GetName() string{returns.Name
}func (s *SellCommand) SetStockReceiver(stockReceiver *StockReceiver) {
s.stockReceiver=stockReceiver
}//命令类调用执行者来自行真正的动作 func (s *SellCommand) Execute() {
fmt.Println("SellCommand::Execute()")
s.stockReceiver.Sell()
}
命令调用类
//CommandInvoker.go 命令调用类，通过关联命令来执行命令的调用 type CommandInvoker struct{
NamestringcommandList []Command
}func (c *CommandInvoker) GetName() string{returnc.Name
}//储存命令 func (c *CommandInvoker) TakeOrder(command Command) {
fmt.Println("CommandInvoker::TakeOrder()" +command.GetName())
c.commandList= append(c.commandList, command)
}//统一执行 func (c *CommandInvoker) ExecuteOrders() {
fmt.Println("CommandInvoker::ExecuteOrders()")for _, command := rangec.commandList {
command.Execute()
}//命令执行后清除 c.commandList = c.commandList[:0]
}
命令接收执行类
//StockReceiver.go 命令模式真正的执行类，不直接对外，通过command来调用 type StockReceiver struct{
NamestringNumint}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) + "]")
}
测试调用
//main包下的main入口方法 funcmain() {
fmt.Println("test start:")/** 命令模式是客户端通过一个命令执行者invoker，去执行某个命令command
* 而命令则调用了业务类receiver的具体动作，从而完成真正的执行
* 这种方式将命令和执行者进行了有效解耦。*/ //先声明一个被操作对象，也就是接收者 var stock1 = &src.StockReceiver{
Name:"Apple",
Num:200,
}//再声明具体的命令 var buyCommand = &src.BuyCommand{
Name:"buyCommand",
}
buyCommand.SetStockReceiver(stock1)var sellCommand = &src.SellCommand{
Name:"sellCommand",
}
sellCommand.SetStockReceiver(stock1)//最后声明调用者，由调用者来执行具体命令 var invoker = &src.CommandInvoker{
Name:"invoker",
}
invoker.TakeOrder(buyCommand)
invoker.TakeOrder(sellCommand)
invoker.ExecuteOrders()//再执行一只股票 var stock2 = &src.StockReceiver{
Name:"Google",
Num:100,
}var buyCommand2 = &src.BuyCommand{
Name:"buyCommand2",
}
buyCommand2.SetStockReceiver(stock2)
invoker.TakeOrder(buyCommand2)
invoker.ExecuteOrders()
}
C语言代码
基础对象定义
//func.h文件，基础命令结构体head #include <stdio.h>#include<stdlib.h>#include<stdbool.h>#include<string.h> //基础命令结构体 typedef structCommand
{char name[50];struct StockReceiver *stock_receiver;void (*set_stock_receiver)(struct Command *command, struct StockReceiver *);void (*execute)(struct Command *);
} Command;//接受者对象 typedef structStockReceiver
{char name[50];intnum;void (*buy)(struct StockReceiver *);void (*sell)(struct StockReceiver *);
} StockReceiver;
StockReceiver*stock_receiver_constructor(char *name, intnum);//继承命令结构体 typedef structBuyCommand
{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);//继承命令结构体 typedef structSellCommand
{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);//命令执行者 typedef structCommandInvoker
{char name[50];void (*take_order)(struct CommandInvoker *invoker, Command *command);void (*execute_orders)(struct CommandInvoker *invoker);//数组命令列表，记录待执行的命令对象 struct Command **command_list;//数组长度记录 intcommand_list_size;//若是柔性数组，则放在结构体最后，可以动态追加内容//struct Command *command_list[]; } CommandInvoker;
CommandInvoker*command_invoker_constructor(char *name);
具体命令类，可以多个命令
//buy_command.c 购买命令，操作receiver，实现了抽象命令类 #include "func.h" //购买命令，操作receiver，实现了抽象命令类 void set_buy_stock_receiver(BuyCommand *command, StockReceiver *receiver)
{
command->stock_receiver =receiver;
}//命令类调用执行者来自行真正的动作 void buy_command_execute(Command *command)
{
printf("\r\n BuyCommand::execute() [command->name=%s]", command->name);
command->stock_receiver->buy(command->stock_receiver);
}//创建Buy命令对象 BuyCommand *buy_command_constructor(char *name)
{
Command*command = (Command *)malloc(sizeof(Command));
strncpy(command->name, name, 50);
command->execute = &buy_command_execute;//转为BuyCommand BuyCommand *buy_command = (BuyCommand *)command;
buy_command->set_stock_receiver = &set_buy_stock_receiver;returnbuy_command;
}//sell_command.c 出售命令，操作receiver，实现了抽象命令类 #include "func.h" //出售命令，操作receiver，实现了抽象命令类 void set_sell_stock_receiver(SellCommand *command, StockReceiver *receiver) {
command->stock_receiver =receiver;
}//命令类调用执行者来自行真正的动作 void sell_command_execute(Command *command) {
printf("\r\n SellCommand::execute() [command->name=%s]", command->name);
command->stock_receiver->sell(command->stock_receiver);
}//创建Sell命令对象 SellCommand *sell_command_constructor(char *name)
{
Command*command = (Command *)malloc(sizeof(Command));
strncpy(command->name, name, 50);
command->execute = &sell_command_execute;//转为SellCommand SellCommand *buy_command = (SellCommand *)command;
buy_command->set_stock_receiver = &set_sell_stock_receiver;returnbuy_command;
}
命令调用类
//command_invoker.c 命令调用类，通过关联命令来执行命令的调用 #include "func.h" /*命令调用类，通过关联命令来实行命令的调用
在命令模式中，Invoker（调用者）是一个可选的组件，
它负责将Command对象传递给Receiver，
并调用Command对象的execute方法来执行命令。
Invoker在实现命令模式时可以有多种实现方式。*/ void print_command_list(Command **list, intcommand_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);
}
}//把命令存储到调用者的命令列表 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);//列表长度增加1位 int new_command_list_size = invoker->command_list_size + 1;/*如果采取柔性数组，则无需申请新空间和复制内容*/ //把原列表命令暂存下来 Command **old_command_list = invoker->command_list;//给命令列表申请新空间 invoker->command_list = (Command **)calloc(new_command_list_size, sizeof(Command *));//复制原有命令到命令列表，如果采取柔性数组则无需复制 for (int i = 0; i < invoker->command_list_size; i++)
{
invoker->command_list[i] =old_command_list[i];
}free(old_command_list);//把新的命令添加列表最后 invoker->command_list[new_command_list_size - 1] =command;
invoker->command_list_size =new_command_list_size;//打印当前有多少命令//print_command_list(invoker->command_list, invoker->command_list_size); }//统一执行全部命令 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;
}//命令执行完后清除命令列表 invoker->command_list_size = 0;
invoker->command_list = (Command **)calloc(0, sizeof(Command *));
}//初始化CommandInvoker命令对象 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;returninvoker;
}
命令接收执行类
//stock_receiver.c 命令模式真正的执行类，不直接对外，通过command来调用 #include "func.h" /*命令模式真正的执行类，不直接对外，通过command来调用*/ 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);
}//创建StockReceiver命令对象 StockReceiver *stock_receiver_constructor(char *name, intnum)
{
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;returnreceiver;
}
测试调用
#include "../src/func.h" int main(void)
{
printf("test start:\r\n");/** 命令模式是一种行为设计模式，它将请求或操作封装成单个对象，并使其可以被参数化和延迟执行。
* 在命令模式中，客户端通过一个命令执行者invoker，去执行某个命令command
* 而命令则调用了业务类receiver的具体动作，从而完成真正的执行
* 这种方式将命令和执行者进行了有效解耦。*/ //先声明一个被操作对象，也就是接收者 StockReceiver *stocker_receiver1 = stock_receiver_constructor("Apple", 200);//再声明具体的命令 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);//最后声明调用者，由调用者来执行具体命令 CommandInvoker *invoker = command_invoker_constructor("invoker");
invoker->take_order(invoker, (Command *)buy_command);
invoker->take_order(invoker, (Command *)sell_command);
invoker->execute_orders(invoker);//再执行一只股票，声明新的接受者 StockReceiver *stock_receiver2 = stock_receiver_constructor("Google", 100);
BuyCommand*buy_command2 = buy_command_constructor("buy_command2");//这次只有buy命令 buy_command2->set_stock_receiver(buy_command2, stock_receiver2);//还用原来的invoker，或者新建invoker invoker->take_order(invoker, (Command *)buy_command2);
invoker->execute_orders(invoker);return 0;
}
更多语言版本
不同语言实现设计模式源码：
https://github.com/microwind/design-pattern