balking设计模式

• 当现在不适合这个操作，或是没有必要进行这个操作时就直接放弃这个操作而回去。这个就是Balking模式。
• 例如王某在餐厅吃饭，当王某需要点餐时喊服务员需要点餐。当服务员A和B都注意到了王某点餐的示意，这时服务员B看到服务员A已经去响应了王某的点餐请求，所以服务员B就不会再过去响应王某的点餐请求。
• 相比guarded-suspension设计模式，这是一种更加消极的模式。服务不了直接离开了。
• 操作的数据类

public class BalkingData {
    private final String fileName;

    private String content;

    private boolean changed;

    public BalkingData(String fileName, String content) {
        this.fileName = fileName;
        this.content = content;
        this.changed = true;
    }

    public synchronized void change(String newContent) {
        this.content = newContent;
        this.changed = true;
    }

    public synchronized void save() throws IOException {
        if (!changed) {
            return;
        }

        doSave();
        this.changed = false;
    }

    private void doSave() throws IOException {
        System.out.println(Thread.currentThread().getName() + " calls do save,content=" + content);
        try (Writer writer = new FileWriter(fileName, true)) {
            writer.write(content);
            writer.write("\n");
            writer.flush();
        }
    }
}

• 顾客类

public class CustomerThread extends Thread {

    private final BalkingData balkingData;

    private final Random random = new Random(System.currentTimeMillis());

    public CustomerThread(BalkingData balkingData) {
        super("Customer");
        this.balkingData = balkingData;
    }

    @Override
    public void run() {
        try {
            balkingData.save();
            for (int i = 0; i < 20; i++) {
                balkingData.change("No." + i);
                Thread.sleep(random.nextInt(1000));
                //如果这里运行，说明有离得比较近的服务员能服务
                balkingData.save();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

• 服务员类

public class WaiterThread extends Thread {

    private final BalkingData balkingData;

    public WaiterThread(BalkingData balkingData) {
        super("Waiter");
        this.balkingData = balkingData;
    }

    @Override
    public void run() {
        for (int i = 0; i < 200; i++) {
            try {
                balkingData.save();
                Thread.sleep(1_000L);
            } catch (IOException e) {
                e.printStackTrace();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

• 调用类

public class BalkingClient {
    public static void main(String[] args) {
        BalkingData balkingData = new BalkingData("C:\\workspace\\fortest\\balking.txt", "===BEGIN====");
        new CustomerThread(balkingData).start();
        new WaiterThread(balkingData).start();
    }
}

• 结果

  
  Snipaste_2020-10-06_22-06-33.png