Command概述

Command - 图1

UML概述

Command - 图2

玩具代码案例1 - 模拟Restful框架的设计

手写一个简易的Web Controller MVC

命令注解

RestfulAnnotation

  1. package online.javabook.gof.behavioral.patterns2.command2.restful.commands;
  3. import java.lang.annotation.ElementType;
  4. import java.lang.annotation.Retention;
  5. import java.lang.annotation.RetentionPolicy;
  6. import java.lang.annotation.Target;
  9. @Target(ElementType.METHOD)
  10. @Retention(RetentionPolicy.RUNTIME)
  11. public @interface RestfulAnnotation {
  13.     String path();
  15.     HttpMethod httpMethod();
  17. }
  20. public enum HttpMethod {
  21.     GET,
  22.     POST,
  23.     PUT,
  24.     DELETE
  25. }

命令的实现类

GroupController

  1. package online.javabook.gof.behavioral.patterns2.command2.restful.controller;
  3. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.HttpMethod;
  4. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.RestfulAnnotation;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  9. public class GroupController {
  11.     @RestfulAnnotation(path = "/api/groups", httpMethod = HttpMethod.POST)
  12.     public void createUser(HttpServletRequest request, HttpServletResponse response) {
  13.         System.out.println("create group");
  14.     }
  16.     @RestfulAnnotation(path = "/api/groups", httpMethod = HttpMethod.GET)
  17.     public void readUser(HttpServletRequest request, HttpServletResponse response) {
  18.         System.out.println("read group");
  19.     }
  21.     @RestfulAnnotation(path = "/api/groups", httpMethod = HttpMethod.PUT)
  22.     public void updateUser(HttpServletRequest request, HttpServletResponse response) {
  23.         System.out.println("update group");
  24.     }
  26.     @RestfulAnnotation(path = "/api/groups", httpMethod = HttpMethod.DELETE)
  27.     public void deleteUser(HttpServletRequest request, HttpServletResponse response) {
  28.         System.out.println("delete group");
  29.     }
  30. }

UserController

  1. package online.javabook.gof.behavioral.patterns2.command2.restful.controller;
  3. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.HttpMethod;
  4. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.RestfulAnnotation;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  9. public class UserController {
  11.     @RestfulAnnotation(path = "/api/users", httpMethod = HttpMethod.POST)
  12.     public void createUser(HttpServletRequest request, HttpServletResponse response) {
  13.         System.out.println("create user");
  14.     }
  16.     @RestfulAnnotation(path = "/api/users", httpMethod = HttpMethod.GET)
  17.     public void readUser(HttpServletRequest request, HttpServletResponse response) {
  18.         System.out.println("read user");
  19.     }
  21.     @RestfulAnnotation(path = "/api/users", httpMethod = HttpMethod.PUT)
  22.     public void updateUser(HttpServletRequest request, HttpServletResponse response) {
  23.         System.out.println("update user");
  24.     }
  26.     @RestfulAnnotation(path = "/api/users", httpMethod = HttpMethod.DELETE)
  27.     public void deleteUser(HttpServletRequest request, HttpServletResponse response) {
  28.         System.out.println("delete user");
  29.     }
  30. }

命令的注册器和执行器

RestfulRegister

  1. package online.javabook.gof.behavioral.patterns2.command2.restful.register;
  3. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.HttpMethod;
  4. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.RestfulInstance;
  5. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.RestfulAnnotation;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.lang.reflect.InvocationTargetException;
  10. import java.lang.reflect.Method;
  11. import java.util.HashMap;
  12. import java.util.Map;
  14. public class RestfulRegister {
  16.     private Map<String, RestfulInstance> restfulApiHashMap = new HashMap<>();
  18.     public void register(Class controllerClass) throws IllegalAccessException, InstantiationException {
  19.         Object controller = controllerClass.newInstance();
  20.         Method[] methods = controllerClass.getMethods();
  22.         for (Method method : methods) {
  23.             RestfulAnnotation annotation = method.getAnnotation(RestfulAnnotation.class);
  24.             if(annotation!= null) {
  25.                 String restfulApiPath = annotation.path() + ":" + annotation.httpMethod();
  26.                 RestfulInstance restfulApi = new RestfulInstance(controller, method);
  27.                 restfulApiHashMap.put(restfulApiPath, restfulApi);
  28.             }
  29.         }
  30.     }
  32.     private RestfulInstance discover(String path, HttpMethod httpMethod) {
  33.         String restfulApiPath = path + ":" + httpMethod;
  34.         return restfulApiHashMap.get(restfulApiPath);
  35.     }
  37.     public void doRestful(String path, HttpMethod httpMethod, HttpServletRequest request, HttpServletResponse response) throws InvocationTargetException, IllegalAccessException {
  38.         discover(path, httpMethod).execute(request, response);
  39.     }
  40. }

RestfulInstance

  1. package online.javabook.gof.behavioral.patterns2.command2.restful.commands;
  3. import javax.servlet.http.HttpServletRequest;
  4. import javax.servlet.http.HttpServletResponse;
  5. import java.lang.reflect.InvocationTargetException;
  6. import java.lang.reflect.Method;
  8. public class RestfulInstance {
  9.     private Object controller;
  10.     private Method method;
  12.     public RestfulInstance(Object controller, Method method) {
  13.         this.controller = controller;
  14.         this.method = method;
  15.     }
  17.     public void execute(HttpServletRequest request, HttpServletResponse response) throws InvocationTargetException, IllegalAccessException {
  18.         method.invoke(controller, request, response);
  19.     }
  20. }

命令执行者与命令

Main

  1. package online.javabook.gof.behavioral.patterns2.command2.restful.app;
  3. import online.javabook.gof.behavioral.patterns2.command2.restful.commands.HttpMethod;
  4. import online.javabook.gof.behavioral.patterns2.command2.restful.controller.GroupController;
  5. import online.javabook.gof.behavioral.patterns2.command2.restful.controller.UserController;
  6. import online.javabook.gof.behavioral.patterns2.command2.restful.register.RestfulRegister;
  7. import org.mockito.Mockito;
  9. import javax.servlet.http.HttpServletRequest;
  10. import javax.servlet.http.HttpServletResponse;
  11. import java.lang.reflect.InvocationTargetException;
  13. public class Main {
  14.     public static void main(String[] args) throws InstantiationException, IllegalAccessException, InvocationTargetException {
  15.         RestfulRegister restfulRegister = new RestfulRegister();
  16.         restfulRegister.register(UserController.class);
  17.         restfulRegister.register(GroupController.class);
  19.         HttpServletRequest  mockedRequest = Mockito.mock(HttpServletRequest.class);
  20.         HttpServletResponse  mockedResponse = Mockito.mock(HttpServletResponse.class);
  21.         restfulRegister.doRestful("/api/users", HttpMethod.POST, mockedRequest, mockedResponse);
  22.         restfulRegister.doRestful("/api/users", HttpMethod.GET, mockedRequest, mockedResponse);
  23.         restfulRegister.doRestful("/api/users", HttpMethod.PUT, mockedRequest, mockedResponse);
  24.         restfulRegister.doRestful("/api/users", HttpMethod.DELETE, mockedRequest, mockedResponse);
  26.         restfulRegister.doRestful("/api/groups", HttpMethod.POST, mockedRequest, mockedResponse);
  27.         restfulRegister.doRestful("/api/groups", HttpMethod.GET, mockedRequest, mockedResponse);
  28.         restfulRegister.doRestful("/api/groups", HttpMethod.PUT, mockedRequest, mockedResponse);
  29.         restfulRegister.doRestful("/api/groups", HttpMethod.DELETE, mockedRequest, mockedResponse);
  30.     }
  31. }

Console

  1. create user
  2. read user
  3. update user
  4. delete user
  5. create group
  6. read group
  7. update group
  8. delete group

玩具代码案例2 - 模拟客户端编辑器的命令菜单

事实上你会发现GOF中的大多数设计模式都和客户端应用有着非常大的渊源，可能是设计模式提出的时候还是客户端应用的黄金时期。命令模式通常会在命令接口中提供可供操作的上下文数据，比如这个案例中的Editor。

命令接口

ICommand

  1. package online.javabook.gof.behavioral.patterns2.command1.editor.commands;
  3. import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;
  5. public interface ICommand {
  7.     void execute(Editor editor);
  8. }

命令的实现类

CommandAnnotation

命令注解类型，我们在传统的命令模式中增加了注解来动态处理命令。设计模式之初Java应该还没有提供注解的支持。注解融入到设计模式之中也是非常方便的。

  1. package online.javabook.gof.behavioral.patterns2.command1.editor.commands;
  3. import java.lang.annotation.ElementType;
  4. import java.lang.annotation.Retention;
  5. import java.lang.annotation.RetentionPolicy;
  6. import java.lang.annotation.Target;
  8. @Target(ElementType.TYPE)
  9. @Retention(RetentionPolicy.RUNTIME)
  10. public @interface CommandAnnotation {
  11.     public String name();
  12. }

CopyCommand

  1. package online.javabook.gof.behavioral.patterns2.command1.editor.commands;
  3. import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;
  5. @CommandAnnotation(name="copy")
  6. public class CopyCommand implements ICommand {
  7.     @Override
  8.     public void execute(Editor editor) {
  9.         System.out.println("click copy button");
  10.     }
  11. }

CutCommand

  1. package online.javabook.gof.behavioral.patterns2.command1.editor.commands;
  3. import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;
  5. @CommandAnnotation(name="cut")
  6. public class CutCommand implements ICommand {
  7.     @Override
  8.     public void execute(Editor editor) {
  9.         System.out.println("click cut button");
  10.     }
  11. }

NewCommand

package online.javabook.gof.behavioral.patterns2.command1.editor.commands;

import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;

@CommandAnnotation(name="new")
public class NewCommand implements ICommand {
    @Override
    public void execute(Editor editor) {
        System.out.println("click new button");
    }
}

OpenCommand

package online.javabook.gof.behavioral.patterns2.command1.editor.commands;

import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;

@CommandAnnotation(name="open")
public class OpenCommand implements ICommand {
    @Override
    public void execute(Editor editor) {
        System.out.println("click open button");
    }
}

PasteCommand

package online.javabook.gof.behavioral.patterns2.command1.editor.commands;

import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;

@CommandAnnotation(name="paste")
public class PasteCommand implements ICommand {
    @Override
    public void execute(Editor editor) {
        System.out.println("click paste button");
    }
}

命令的执行器

Editor

这个案例中编辑器作为命令的容器，管理者和执行者。

package online.javabook.gof.behavioral.patterns2.command1.editor.context;

import online.javabook.gof.behavioral.patterns2.command1.editor.commands.CommandAnnotation;
import online.javabook.gof.behavioral.patterns2.command1.editor.commands.ICommand;

import java.util.HashMap;
import java.util.Map;

public class Editor {

    private Map<String, ICommand> commandRegister = new HashMap<>();

    public void registerCommand(Class<? extends ICommand> commandClass) throws IllegalAccessException, InstantiationException {
        CommandAnnotation commandAnnotation = commandClass.getAnnotation(CommandAnnotation.class);
        ICommand command = commandClass.newInstance();
        commandRegister.put(commandAnnotation.name(), command);
    }

    public ICommand discoverCommand(String commandName) {
        return commandRegister.get(commandName);
    }

    public void doCommand(String commandName) {
        discoverCommand(commandName).execute(this);
    }
}

命令执行者与命令

Main

package online.javabook.gof.behavioral.patterns2.command1.editor.app;

import online.javabook.gof.behavioral.patterns2.command1.editor.commands.*;
import online.javabook.gof.behavioral.patterns2.command1.editor.context.Editor;

public class Main {
    public static void main(String[] args) throws InstantiationException, IllegalAccessException {
        Editor editor = new Editor();
        editor.registerCommand(NewCommand.class);
        editor.registerCommand(OpenCommand.class);
        editor.registerCommand(CopyCommand.class);
        editor.registerCommand(CutCommand.class);
        editor.registerCommand(PasteCommand.class);

        editor.doCommand("new");
        editor.doCommand("open");
        editor.doCommand("copy");
        editor.doCommand("cut");
        editor.doCommand("paste");
    }
}

Console

click new button
click open button
click copy button
click cut button
click paste button