Java設計模式——觀察者模式的靈活應用

靈感來源於一個豬隊友給個人題目java

 

 看到這個,我抓住的關鍵字是:任何子任務失敗,要通知全部子任務執行取消邏輯。dom

 這不就是消息廣播嗎?觀察者模式!ide

幹活

首先是收聽者測試

package com.example.broadcast;

/**
 * 每一個節點便是廣播者,也是收聽者
 */
public interface Listener {

    /**
     * 設置調度中心
     */
    void setCenter(DispatchCenter center);

    /**
     * 主動通知其它收聽者
     */
    void notice(String msg);

    /**
     * 本身收到通知的處理邏輯
     * @param msg
     */
    void whenReceived(String msg);

    /**
     * 收聽者標誌:惟一
     * @return
     */
    String identify();

}

而後是調度中心this

package com.example.broadcast;

/**
 * 調度中心
 */
public interface DispatchCenter {

    /**
     * 廣播
     * @param own 廣播的時候,要排除本身
     * @param msg 廣播消息
     */
    void broadcast(String own, String msg);

    /**
     * 添加收聽者
     * @param listener
     */
    void addListener(Listener listener);

}

調度中心實現spa

package com.example.broadcast;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;


public class DispatchCenterImpl implements DispatchCenter {

    private static final Map<String, Listener> MAP = new ConcurrentHashMap<>();

    @Override
    public void broadcast(String own, String msg) {
        MAP.forEach((k,v) -> {
            // 不用給本身發通知
            if (!k.equals(own)){
                v.whenReceived(msg);
            }
        });
    }

    @Override
    public void addListener(Listener listener) {
        listener.setCenter(this);
        MAP.put(listener.identify(), listener);
    }
}

剩下三個收聽者線程

package com.example.broadcast;

import java.util.UUID;

public class ListenerA implements Listener {

    private DispatchCenter center;
    private String identify;

    public ListenerA() {
        identify = UUID.randomUUID().toString();
    }

    @Override
    public void setCenter(DispatchCenter center) {
        this.center = center;
    }

    @Override
    public void notice(String msg) {
        center.broadcast(identify, msg);
    }

    @Override
    public void whenReceived(String msg) {
        System.out.println(this.getClass().getName() + "收到消息:" + msg);
    }

    @Override
    public String identify() {
        return identify;
    }
}

B和C除了類名不同,其餘都同樣,再也不贅述。目錄以下3d

 

測試

package com.example.broadcast;


import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {


    public static void main(String[] args) {
        DispatchCenter center = new DispatchCenterImpl();
        ListenerA listenerA = new ListenerA();
        ListenerB listenerB = new ListenerB();
        ListenerC listenerC = new ListenerC();
        center.addListener(listenerA);
        center.addListener(listenerB);
        center.addListener(listenerC);

        ExecutorService executorService = Executors.newFixedThreadPool(3);

        // A觸發1條事件
        executorService.submit(() -> {
            int i = 1;
            while (i > 0){
                listenerA.notice(listenerA.getClass().getName() + "說:我有" + new Random().nextInt(1000000) + "元");
                i--;
            }
        });
        // B觸發2條事件
        executorService.submit(() -> {
            int i = 2;
            while (i > 0){
                listenerB.notice(listenerB.getClass().getName() + "說:我有" + new Random().nextInt(1000000) + "元");
                i--;
            }
        });
        // C觸發3條事件
        executorService.submit(() -> {
            int i = 3;
            while (i > 0){
                listenerC.notice(listenerC.getClass().getName() + "說:我有" + new Random().nextInt(1000000) + "元");
                i--;
            }
        });

        executorService.shutdown();

    }


}

輸出:code

 

 流程圖

 

 當其中的B節點,發生了錯誤,除了把本身處理好以外blog

1. 向調度中心發送廣播請求,並攜帶須要的消息

2. 調度中心遍歷收聽者,挨個通知(執行)每個收聽者接受消息的邏輯

 

關於中止任務

由於題目要求,【快速取消】全部子任務

關於線程中止的方法也有不少:

1. 優雅退出run方法

2. 暴力stop

3. run方法拋出異常

 

若是說要求,A異常了,B和C收到消息以後,線程當即中止,不能有一點遲疑,說實話我還沒想到該怎麼作。由於你要知道,實際上的任務的run方法內部,不太多是個while循環,人家可能就是個順序執行,因此中止標誌位的方式,並不適用。

而其它的方法,我也沒想到很好的。我只能寫個按照標誌位中止的「玩具」

修改三個收聽者代碼和測試類

package com.example.broadcast;

import lombok.SneakyThrows;

import java.util.Random;
import java.util.UUID;

public class ListenerA implements Listener,Runnable {

    private DispatchCenter center;
    private String identify;

    public ListenerA() {
        identify = UUID.randomUUID().toString();
    }

    @Override
    public void setCenter(DispatchCenter center) {
        this.center = center;
    }

    @Override
    public void notice(String msg) {
        center.broadcast(identify, msg);
    }

    @Override
    public void whenReceived(String msg) {
        System.out.println(this.getClass().getName() + "收到消息:" + msg);
    }

    @Override
    public String identify() {
        return identify;
    }

    @SneakyThrows
    @Override
    public void run() {
        // 5秒以後,模擬發生異常
        Thread.sleep(5000);
        notice(this.getClass().getName() + "說:我有" + new Random().nextInt(1000000) + "元");
        System.out.println(this.getClass().getName() + "程序異常,並已經傳播了消息...");
    }
}
package com.example.broadcast;

import lombok.SneakyThrows;

import java.util.UUID;

public class ListenerB implements Listener,Runnable {

    private DispatchCenter center;
    private String identify;
    private volatile Boolean stopFlag = false;

    public ListenerB() {
        identify = UUID.randomUUID().toString();
    }

    @Override
    public void setCenter(DispatchCenter center) {
        this.center = center;
    }

    @Override
    public void notice(String msg) {
        center.broadcast(identify, msg);
    }

    @Override
    public void whenReceived(String msg) {
        System.out.println(this.getClass().getName() + "_" + Thread.currentThread().getName() + "收到消息:" + msg);
        // 中止當前線程
        stopFlag = true;
    }

    @Override
    public String identify() {
        return identify;
    }

    @SneakyThrows
    @Override
    public void run() {
        while (!stopFlag){
            Thread.sleep(1000);
            System.out.println(this.getClass().getName() + "_" + Thread.currentThread().getName() + "__B在執行任務");
        }
        System.out.println(this.getClass().getName() + "_" + Thread.currentThread().getName() + "__B Dead");
    }
}
package com.example.broadcast;

import lombok.SneakyThrows;

import java.util.UUID;

public class ListenerC implements Listener,Runnable {

    private DispatchCenter center;
    private String identify;
    private volatile Boolean stopFlag = false;

    public ListenerC() {
        identify = UUID.randomUUID().toString();
    }

    @Override
    public void setCenter(DispatchCenter center) {
        this.center = center;
    }

    @Override
    public void notice(String msg) {
        center.broadcast(identify, msg);
    }

    @Override
    public void whenReceived(String msg) {
        System.out.println(this.getClass().getName() + "_" + Thread.currentThread().getName() + "收到消息:" + msg);
        // 中止當前線程
        stopFlag = true;
    }

    @Override
    public String identify() {
        return identify;
    }

    @SneakyThrows
    @Override
    public void run() {
        while (!stopFlag){
            Thread.sleep(1000);
            System.out.println(this.getClass().getName() + "_" + Thread.currentThread().getName() + "__C在執行任務");
        }
        System.out.println(this.getClass().getName() + "_" + Thread.currentThread().getName() + "__C Dead");
    }
}

測試

package com.example.broadcast;


import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Main {


    public static void main(String[] args) {
        DispatchCenter center = new DispatchCenterImpl();
        ListenerA listenerA = new ListenerA();
        ListenerB listenerB = new ListenerB();
        ListenerC listenerC = new ListenerC();
        center.addListener(listenerA);
        center.addListener(listenerB);
        center.addListener(listenerC);

        ExecutorService executorService = Executors.newFixedThreadPool(3);

        // A
        executorService.submit(listenerA);
        // B
        executorService.submit(listenerB);
        // C
        executorService.submit(listenerC);

        executorService.shutdown();

    }


}

 

 

這個是這麼多年第一個發到首頁的,就是想問下你們怎樣解決這種狀況下的線程中止問題

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