Android 架构师之路11 设计模式之命令模式

Android 架构师之路 目录

1、命令模式概念

1.1 介绍

命令模式（Command Pattern）是一种数据驱动的设计模式，它属于行为型模式。请求以命令的形式包裹在对象中，并传给调用对象。调用对象寻找可以处理该命令的合适的对象，并把该命令传给相应的对象，该对象执行命令。

1.2 定义

将一个请求封装为一个对象，从而使你可用不同的请求对客户进行参数化，对请求排队或记录请求日志。以及支持可撤销的操作。

1.3 使用场景

• 系统需要将请求调用者和请求接收者解耦，使得调用者和接收者不直接交互。
• 系统需要在不同的时间指定请求、将请求排队（如：线程池+工作队列）和执行请求。
• 系统需要支持命令的撤销(Undo)操作和恢复(Redo)操作。
• 系统需要将一组操作组合在一起，即支持宏命令。

2、命令模式UML类图

命令模式UML类图

• Command（抽象命令类）：抽象出命令对象，可以根据不同的命令类型。写出不同的实现类

• ConcreteCommand（具体命令类）：实现了抽象命令对象的具体实现

• Invoker（调用者/请求者）：请求的发送者，它通过命令对象来执行请求。一个调用者并不需要在设计时确定其接收者，因此它只与抽象命令来之间存在关联。在程序运行时，将调用命令对象的execute() ，间接调用接收者的相关操作。

• Receiver（接收者）：接收者执行与请求相关的操作，真正执行命令的对象。具体实现对请求的业务处理。未抽象前，实际执行操作内容的对象。

• Client（客户端）：在客户类中需要创建调用者对象，具体命令类对象，在创建具体命令对象时指定对应的接收者。发送者和接收者之间没有之间关系,都通过命令对象来调用。

3、命令模式代码实现

俄罗斯方块游戏
向下方块、向右方块、向左方块...,每一个方向都是一个命令

Command：

public interface ICommand extends Serializable {
    void execute();
}

ConcreteCommand：

public class LeftCommand implements ICommand {
    private Receiver receiver;
    public LeftCommand(Receiver receiver) {
        this.receiver = receiver;
    }
    @Override
    public void execute() {
        /**
         * 执行之前干一些事情
         *  例如 存档
         */
        this.receiver.onLeft();
    }
}


public class RightCommand implements ICommand {
    private Receiver receiver;
    public RightCommand(Receiver receiver) {
        this.receiver = receiver;
    }
    @Override
    public void execute() {
        this.receiver.onRight();
    }

}



public class BottomCommand implements ICommand {
    private Receiver receiver;
    public BottomCommand(Receiver receiver) {
        this.receiver = receiver;
    }
    @Override
    public void execute() {
        this.receiver.onBottom();
    }
}


public class TransfromCommand implements ICommand {
    private Receiver receiver;

    public TransfromCommand(Receiver receiver) {
        this.receiver = receiver;
    }

    @Override
    public void execute() {
        this.receiver.onTransformation();
    }


}

Invoker：

public class Invoker {
    private ICommand leftCommand;
    private ICommand rightCommand;
    private ICommand bottomCommand;
    private ICommand transfromCommand;
    private List<ICommand> commandList = new ArrayList<>();

    public Invoker() {
    }

    public Invoker(ICommand leftCommand, ICommand rightCommand, ICommand bottomCommand, ICommand transfromCommand) {
        this.leftCommand = leftCommand;
        this.rightCommand = rightCommand;
        this.bottomCommand = bottomCommand;
        this.transfromCommand = transfromCommand;
    }

    public void toLeft() {
        this.leftCommand.execute();
        commandList.add(leftCommand);
    }

    public void toRight() {
        this.rightCommand.execute();
        commandList.add(rightCommand);
    }

    public void toBottom() {
        this.bottomCommand.execute();
        commandList.add(bottomCommand);
    }

    public void toTransfrom() {
        this.transfromCommand.execute();
        commandList.add(transfromCommand);
    }

    /**
     * 回退
     */
    public void fallback() {
        if (commandList.size() > 0) {
            commandList.remove(commandList.size() - 1);
        }
    }

    /**
     * 存档
     */
    public void saveArchive() {
        Utils.serializable("gameOperation", commandList);
    }

    /**
     * 读档
     */
    public void loadArchive() {
        List<ICommand> list = Utils.deserialize("gameOperation");
        this.commandList.clear();
        this.commandList.addAll(list);
        for (ICommand command : list) {
            command.execute();
        }
    }
}

Receiver：

public class Receiver implements Serializable {

    public void onLeft() {
        System.out.println("向左");
    }

    public void onRight() {
        System.out.println("向右");
    }

    public void onBottom() {
        System.out.println("向下");
    }

    public void onTransformation() {
        System.out.println("变形");
    }
}

存档、读档工具类：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.List;


public class Utils {
    /**
     * 序列化订单对象
     */
    public static void serializable(String name,
                                    List<ICommand> commandList) {
        // 序列化对象的流
        ObjectOutputStream outputStream = null;
        try {
            outputStream = new ObjectOutputStream(new FileOutputStream(
                    new File("C:\\Users\\Administrator\\Desktop\\" + name + ".txt")));
            outputStream.writeObject(commandList);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (outputStream != null) {
                try {
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static List<ICommand> deserialize(String name) {
        ObjectInputStream objectInputStream = null;
        try {
            objectInputStream = new ObjectInputStream(new FileInputStream(
                    new File("C:\\Users\\Administrator\\Desktop\\"
                            + name + ".txt")));
            Object readObject = objectInputStream.readObject();
            return (List<ICommand>) readObject;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

Client ：

public class Client {

    /**
     * @param args
     */
    public static void main(String[] args) {
        /**
         * 接收者
         */
        Receiver receiver = new Receiver();

        // 命令对象
        ICommand leftCommand = new LeftCommand(receiver);
        ICommand rightCommand = new RightCommand(receiver);
        ICommand bottomCommand = new BottomCommand(receiver);
        ICommand transfromCommand = new TransfromCommand(receiver);

        //请求者
        Invoker invoker = new Invoker(leftCommand, rightCommand, bottomCommand, transfromCommand);
        invoker.toLeft();
        invoker.toRight();
        invoker.toBottom();
        invoker.toTransfrom();

        //序列化存档
        System.out.println("----存档----");
        invoker.saveArchive();

        invoker.toBottom();


        System.out.println("----读档----");
        //读档
        invoker.loadArchive();
    }
}

结果输出：

向左
向右
向下
变形
----存档----
向下
----读档----
向左
向右
向下
变形

4、命令模式Android中使用

IHttpCommand相当于命令接口Command：

/**
 * 网络请求命令接口
 *
 * 以前采用Map集合传入， 现在面向接口编程
 * Created by Xionghu on 2017/7/4.
 * Desc:
 */

public interface IHttpCommand<T extends IRequestParam> {
    public enum RequestType {
        Default(0), Get(1), Post(2), Delete(3);
        private int type;

        private RequestType(int type) {
            this.type = type;
        }

        public int getType() {
            return type;
        }
    }

    public String execute(Context context, String url, RequestType requestType,
                          T requestParam);
}

SystemHttpCommand 相当于具体命令实现ConcreteCommand：.

OKHttpCommand 省略

public class SystemHttpCommand extends AbsHttpCommand<SystemRequestParam> {
    @Override
    public String executePost(Context context, String url, SystemRequestParam requestParam) {
        //发送请求
        try {
            return HttpUtils.post(url, requestParam.getRequestParam());
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public String executeGet(Context context, String url, SystemRequestParam requestParam) {
        try {
            return HttpUtils.get(url,requestParam.getRequestParam());
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

HttpUtils 相当于接收者Receiver：

public class HttpUtils {

    public static String get(String urlStr, Map<String, Object> paramMap)
            throws Exception {
        // 拼接参数
        StringBuilder params = new StringBuilder(urlStr + "?");
        int i = 0;
        for (String key : paramMap.keySet()) {
            Object value = paramMap.get(key);
            params.append(key);
            params.append("=");
            params.append(value);
            if (i < paramMap.size() - 1) {
                params.append("&");
            }
            i++;
        }
        return get(params.toString());
    }

    public static String get(String urlStr) {
        String result = null;
        try {
            URL url = new URL(urlStr);
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();
            connection.setReadTimeout(5000);
            connection.setRequestMethod("GET");
            connection.setDoInput(true);
            if (connection.getResponseCode() == 200) {
                InputStream inStream = connection.getInputStream();
                result = new String(StreamTool.readInputStream(inStream));
                return result;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

    public static String post(String urlStr, String username, String password)
            throws Exception {
        Map<String, Object> paramMap = new HashMap<String, Object>();
        paramMap.put("username", username);
        paramMap.put("password", password);
        return post(urlStr, paramMap);
    }

    public static String post(String urlStr, Map<String, Object> paramMap)
            throws Exception {
        StringBuffer sb = null;
        // 拼接参数
        StringBuilder params = new StringBuilder();
        int i = 0;
        for (String key : paramMap.keySet()) {
            Object value = paramMap.get(key);
            params.append(key);
            params.append("=");
            params.append(value);
            if (i < paramMap.size() - 1) {
                params.append("&");
            }
            i++;
        }
        // 创建请求地址
        URL url = new URL(urlStr);
        // 打开连接
        HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
        // 设置参数
        httpConn.setDoOutput(true); // 需要输出
        httpConn.setDoInput(true); // 需要输入
        httpConn.setUseCaches(false); // 不允许缓存
        httpConn.setRequestMethod("POST"); // 设置POST方式连接
        // 设置请求属性
        httpConn.setRequestProperty("Charset", "UTF-8");
        // 连接,也可以不用明文connect，使用下面的httpConn.getOutputStream()会自动connect
        httpConn.connect();
        // 建立输入流，向指向的URL传入参数
        DataOutputStream dos = new DataOutputStream(httpConn.getOutputStream());
        dos.writeBytes(params.toString());
        dos.flush();
        dos.close();
        // 获得响应状态
        int resultCode = httpConn.getResponseCode();
        sb = new StringBuffer();
        if (HttpURLConnection.HTTP_OK == resultCode) {
            // 解析服务器返回的数据
            String readLine = new String();
            BufferedReader responseReader = new BufferedReader(
                    new InputStreamReader(httpConn.getInputStream(), "UTF-8"));
            while ((readLine = responseReader.readLine()) != null) {
                sb.append(readLine).append("\n");
            }
            responseReader.close();
            return sb.toString();
        }
        return null;
    }

    public interface OnHttpResultListener {
        public void onResult(String result);
    }
}

HttpTask 相当于请求者Invoker

public class HttpTask extends AsyncTask<String, Void, String> {

    private HttpTask.Builder.Params p;

    protected HttpTask(HttpTask.Builder.Params p) {
        this.p = p;
    }

    @SuppressWarnings("unchecked")
    @Override
    protected String doInBackground(String... params) {
        try {
            // 执行命令
            return this.p.httpCommand.execute(this.p.context, this.p.url,
                    this.p.requestType, this.p.requestParam);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        if (this.p.onHttpResultListener != null) {
            this.p.onHttpResultListener.onResult(result);
        }
    }

    public void builder() {
        execute();
    }

    // 采用Builder设计模式
    public static class Builder {

        private Params p;

        public Builder(Context context, String url,
                       HttpUtils.OnHttpResultListener onHttpResultListener) {
            this.p = new Params(context, url, onHttpResultListener);
        }

        public Builder setRequestType(IHttpCommand.RequestType requestType) {
            this.p.requestType = requestType;
            return this;
        }

        public Builder setRequestParam(IRequestParam requestParam) {
            this.p.requestParam = requestParam;
            return this;
        }

        public Builder setHttpCommand(IHttpCommand httpCommand) {
            this.p.httpCommand = httpCommand;
            return this;
        }

        public HttpTask build() {
            return new HttpTask(p);
        }

        public static class Params {
            public Context context;
            public IHttpCommand.RequestType requestType;
            public String url;
            public IRequestParam requestParam;
            public HttpUtils.OnHttpResultListener onHttpResultListener;
            public IHttpCommand httpCommand;

            public Params(Context context, String url,
                          HttpUtils.OnHttpResultListener onHttpResultListener) {
                this.context = context;
                this.url = url;
                this.requestType = IHttpCommand.RequestType.Get;
                this.httpCommand = new SystemHttpCommand();
                this.requestParam = new SystemRequestParam();
                this.onHttpResultListener = onHttpResultListener;
            }
        }

    }

}

Client ：

        //请求者
        HttpTask.Builder builder = new HttpTask.Builder(this, "", new HttpUtils.OnHttpResultListener() {
            @Override
            public void onResult(String result) {

            }
        });

        IRequestParam requestParam = new SystemRequestParam();
        requestParam.put("","");
        builder.setRequestParam(requestParam)
               .setRequestType(IHttpCommand.RequestType.Post)
               .build()
               .builder();

      //请求者
        HttpTask.Builder builder = new HttpTask.Builder(this, "", new HttpUtils.OnHttpResultListener() {
            @Override
            public void onResult(String result) {

            }
        });
        IRequestParam requestParam = new OKHttpRequestParam();
        requestParam.put("","");
        builder.setRequestParam(requestParam)
                .setHttpCommand(new OKHttpCommand())
                .setRequestType(IHttpCommand.RequestType.Post).build().builder();

整个网络请求架构采用了命令模式
使我们得程序扩展性更加好，耦合降低了（比如 添加setHttpCommand 设置okhttp请求很方便）

5、模式总结

5.1 优点

• 解除了请求者与实现者之间的耦合，降低了系统的耦合度。

• 对请求排队或记录请求日志，支持撤销操作。

• 可以容易地设计一个组合命令。

• 新命令可以容易地加入到系统中。

5.2 缺点

• 因为针对每一个命令都需要设计一个具体命令类，使用命令模式可能会导致系统有过多的具体命令类。