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java延迟队列，java高级面试笔试题

分类: 文章 • 2022-10-06 20:05:09


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java延迟队列，java高级面试笔试题

 

大多数用到定时执行的功能都是用任务调度来做的，单身当碰到类似订餐业务/购物等这种业务就不好处理了，比如购物的订单功能，在你的订单管理中有N个订单，当订单超过十分钟未支付的时候自动释放购物车中的商品，订单失效。这种高频率的延迟任务再用任务调度（定时）实现就得不偿失了。推荐用Java延迟队列来实现，DelayQueue是java.util.concurrent中提供的一个类DelayQueue是一个无界的BlockingQueue,用于放置实现了Delayed接口的对象，其中的对象只能在其到期时才能从队列中中取走。这种队列是有序的，即对头对象的延迟到期时间最长。注意：不能将null元素放置到这种队列中。

 

1、java延迟队列实现方式

 

import java.util.concurrent.Delayed;

import java.util.concurrent.TimeUnit;

import java.util.concurrent.atomic.AtomicLong;

//任务线程 实现delayed接口

public class DelayItem<T extends Runnable> implements Delayed {

//到期时间

private final long time;

//任务对象

private final T task;

//原子类

private static final AtomicLong atomic = new AtomicLong(0);

private final long n;

public DelayItem(long timeout, T t) {

    this.time = System.nanoTime() ＋ timeout;

    this.task = t;

    this.n = atomic.getAndIncrement();

}

//返回与此对象相关的剩余延迟时间，以给定的时间单位表示

public long getDelay(TimeUnit unit) {

    return unit.convert(this.time - System.nanoTime(),TimeUnit.NANOSECONDS);

}

public int compareTo(Delayed other) {

    if(other == this) {

    return 0;

    }

    if(other instanceof DelayItem) {

        DelayItem<?> x = (DelayItem<?>)other;

        long diff = tiem - x.time;

        if(diff < 0) {

            return -1;

        }else if(diff > 0) {

            return 1;

        }else if( n < x.n){

            return -1；

        }else {

            return 1;

        }

        long d = (getDelay(TimeUnit.NANOSECONDS) -           other.getDelay(TimeUnit.NANOSECONDS));

        return (d == 0) ? 0 : ((d < 0) ? -1 : 1);

    }

    public T getTask(){

        return this.task;

    }

    @Override

    public int hashCode(){

        return task.hashCode();

    }

    @Override

    public boolean equals(Object object){

        if(object instanceof DelayItem){

            return object.hashCode() == hashCode() ? true : false;

    }

    return false;

}

}

//管理延迟任务的类

import java.util.Map;

import java.util.concurrent.DelayQueue;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.TimeUnit;

import org.apache.log4j.Logger;

//延迟队列存放有效期对象

public class ItemQueueThread {

private static final Logger logger = Logger.getLogger(this.class);

private ItemQueueThread(){}

//延迟加载（线程安全）

private static class LazyHolder{

    private static ItemQueueThread itemQueueThread = new ItemQueueThread();

}

public static ItemQueueThread getInstance(){

    return LazyHolder.itemQueueThread;

}

//缓存线程池

ExecutorService executor = Executors.newCacheThreadPool();

//线程

private Thread daemonThead;

//初始化线程

public void init() {

    daemonThread = new Thread(() -> {

        try{

            execute();

        }cathc(InterruptedException e){

            e.printStackTrace();

            logger.info(e.getMessage());

        }

    });

    System.out.println("init......start");

    daemonThread.start();

}

private void execute() throws InterrupedException {

    while(true) {

        Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();

        System.out.println("线程数...." + map.size());

        System.out.println(System.currentTimeMills());

        System.out.println(item.size());

        System.out.println("线程状态----" + Thread.currentThread().getState());

        try{

            //从延迟队列中取值，如果没有对象过期责队列一直等待

            DelayItem<?> t1 = item.take();

            if(t1 != null){

                Runnable task = t1.getTask();

                    if(task == null){

                        continue;

                }

                executor.execute(task);

            }

        }catch(Exception e) {

            e.printStackTrace();

            logger.info(e.getMessage());

        }

    }

}

//创建空的延迟队列

private DelayQueue<DelayItem<?>> item = new DelayQueue<>();

//往队列中添加任务

public void put(long time, Runnable task, TimeUnit timeUnit){

    //转换成ns

    long nanoTime = TimeUnit.NANOSECONDS.convert(time,timeUnit);

    DelayItem<?> k = new DelayItem(nanoTime,task);

    item.put(k);_:

}

//结束任务

public boolean endTask(DelayItem<Runnable> task){

    return item.remove(task);

}

}

//把需要延迟的功能代码单独抽取出来作为一个类，继承Runnable实现run方法

public class DataDemo implements Runnable {

    int a = -1;

    public DataDemo(int i){

        this.a = i;

}

@Override

public void run(){

    System.out.println("超时，要撤销订单...." + a);

}

}

//test class

import java.util.Random;

import java.util.concurrent.TimeUnit;

public class DelayTest{

public static void main(String[] args){

    ItemQueueThread  ith = ItemQueueThread.getInstance();

    ith.init();

    Random r = new Random();

    for(int i = 0; i < 5; i++){

        int a = r.nextInt(20);

        System.out.println("预先知道等待时间：" + a);

        DataDemo dd = new DataDemo(a)；//创建一个任务对象

        ith.put(a,dd,TimeUnit.SECONDS);//将任务添加到队列中

    }

}

}

//注意ItemQueueThread的init方法，要在容器初始化的时候就要执行，或在第一次put延迟对象任务之前就要初始化完成，当设定的延迟时间到期时会执行任务对象中的run

}            



import java.util.concurrent.TimeUnit;

import java.util.concurrent.atomic.AtomicLong;

//任务线程 实现delayed接口

public class DelayItem<T extends Runnable> implements Delayed {

//到期时间

private final long time;

//任务对象

private final T task;

//原子类

private static final AtomicLong atomic = new AtomicLong(0);

private final long n;

public DelayItem(long timeout, T t) {

    this.time = System.nanoTime() ＋ timeout;

    this.task = t;

    this.n = atomic.getAndIncrement();

}

//返回与此对象相关的剩余延迟时间，以给定的时间单位表示

public long getDelay(TimeUnit unit) {

    return unit.convert(this.time - System.nanoTime(),TimeUnit.NANOSECONDS);

}

public int compareTo(Delayed other) {

    if(other == this) {

    return 0;

    }

    if(other instanceof DelayItem) {

        DelayItem<?> x = (DelayItem<?>)other;

        long diff = tiem - x.time;

        if(diff < 0) {

            return -1;

        }else if(diff > 0) {

            return 1;

        }else if( n < x.n){

            return -1；

        }else {

            return 1;

        }

        long d = (getDelay(TimeUnit.NANOSECONDS) -           other.getDelay(TimeUnit.NANOSECONDS));

        return (d == 0) ? 0 : ((d < 0) ? -1 : 1);

    }

    public T getTask(){

        return this.task;

    }

    @Override

    public int hashCode(){

        return task.hashCode();

    }

    @Override

    public boolean equals(Object object){

        if(object instanceof DelayItem){

            return object.hashCode() == hashCode() ? true : false;

    }

    return false;

}

}

//管理延迟任务的类

import java.util.Map;

import java.util.concurrent.DelayQueue;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.TimeUnit;

import org.apache.log4j.Logger;

//延迟队列存放有效期对象

public class ItemQueueThread {

private static final Logger logger = Logger.getLogger(this.class);

private ItemQueueThread(){}

//延迟加载（线程安全）

private static class LazyHolder{

    private static ItemQueueThread itemQueueThread = new ItemQueueThread();

}

public static ItemQueueThread getInstance(){

    return LazyHolder.itemQueueThread;

}

//缓存线程池

ExecutorService executor = Executors.newCacheThreadPool();

//线程

private Thread daemonThead;

//初始化线程

public void init() {

    daemonThread = new Thread(() -> {

        try{

            execute();

        }cathc(InterruptedException e){

            e.printStackTrace();

            logger.info(e.getMessage());

        }

    });

    System.out.println("init......start");

    daemonThread.start();

}

private void execute() throws InterrupedException {

    while(true) {

        Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();

        System.out.println("线程数...." + map.size());

        System.out.println(System.currentTimeMills());

        System.out.println(item.size());

        System.out.println("线程状态----" + Thread.currentThread().getState());

        try{

            //从延迟队列中取值，如果没有对象过期责队列一直等待

            DelayItem<?> t1 = item.take();

            if(t1 != null){

                Runnable task = t1.getTask();

                    if(task == null){

                        continue;

                }

                executor.execute(task);

            }

        }catch(Exception e) {

            e.printStackTrace();

            logger.info(e.getMessage());

        }

    }

}

//创建空的延迟队列

private DelayQueue<DelayItem<?>> item = new DelayQueue<>();

//往队列中添加任务

public void put(long time, Runnable task, TimeUnit timeUnit){

    //转换成ns

    long nanoTime = TimeUnit.NANOSECONDS.convert(time,timeUnit);

    DelayItem<?> k = new DelayItem(nanoTime,task);

    item.put(k);_:

}

//结束任务

public boolean endTask(DelayItem<Runnable> task){

    return item.remove(task);

}

}

//把需要延迟的功能代码单独抽取出来作为一个类，继承Runnable实现run方法

public class DataDemo implements Runnable {

    int a = -1;

    public DataDemo(int i){

        this.a = i;

}

@Override

public void run(){

    System.out.println("超时，要撤销订单...." + a);

}

}

//test class

import java.util.Random;

import java.util.concurrent.TimeUnit;

public class DelayTest{

public static void main(String[] args){

    ItemQueueThread  ith = ItemQueueThread.getInstance();

    ith.init();

    Random r = new Random();

    for(int i = 0; i < 5; i++){

        int a = r.nextInt(20);

        System.out.println("预先知道等待时间：" + a);

        DataDemo dd = new DataDemo(a)；//创建一个任务对象

        ith.put(a,dd,TimeUnit.SECONDS);//将任务添加到队列中

    }

}

}

//注意ItemQueueThread的init方法，要在容器初始化的时候就要执行，或在第一次put延迟对象任务之前就要初始化完成，当设定的延迟时间到期时会执行任务对象中的run

}

 

2、定时任务实现方式

引入quartz包

 

import org.quartz.Job;

import org.quartz.JobBuilder;

import org.quartz.JobDetail;

import org.quartz.JobExecutionContext;

import org.quartz.JobExecutionException;

import org.quartz.Scheduler;

import org.quartz.SchedulerException;

import org.quartz.SimpleScheduleBuilder;

import org.quartz.Trigger;

import org.quartz.TriggerBuilder;

import org.quartz.impl.StdSchedulerFactory;

public class DeplayQuartzImpl implements Job{

    @Override

    public void execute(JobExecutionContext context) throws JobExecutionException {

        //doing somethings 
        System.out.println("going scan database...");

    }

    

    public static void main(String[] args) throws SchedulerException {

        

        //create task

        JobDetail jobDetail = JobBuilder.newJob(DeplayQuartzImpl.class).withIdentity("job_1", "group_1").build();

        

        //create trigger

        Trigger trigger = TriggerBuilder.newTrigger()

                            .withIdentity("trigger_1", "group_trigger")

                            .withSchedule(SimpleScheduleBuilder.simpleSchedule()

                            .withIntervalInSeconds(3).repeatForever())

                            .build();

        Scheduler scheduler = new StdSchedulerFactory().getScheduler();

        

        //put task into trigger

        scheduler.scheduleJob(jobDetail, trigger);

        scheduler.start();

    }

}

 

实现java的Delayed接口简介版

 

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.DelayQueue;

import java.util.concurrent.Delayed;

import java.util.concurrent.TimeUnit;

public class JdkDelayImpl implements Delayed{

    private String orderId;

    private long timeout;

    

    

    public JdkDelayImpl(String orderId, long timeout) {

        this.orderId = orderId;

        this.timeout = timeout + System.nanoTime();

    }

    @Override

    public int compareTo(Delayed delayed) {

        if(delayed == this)

            return 0;

        JdkDelayImpl t = (JdkDelayImpl) delayed;

        long d = (getDelay(TimeUnit.NANOSECONDS) - t.getDelay(TimeUnit.NANOSECONDS));

        return (d == 0) ? 0 : ((d < 0) ? -1 : 1);

    }

    @Override

    public long getDelay(TimeUnit unit) {

        return unit.convert(timeout - System.nanoTime(), TimeUnit.NANOSECONDS );

    }

    

    void print() {

        System.out.println(orderId + " order will being delete...");

    }

    

    

    public static void main(String[] args) {

        List<String> list = new ArrayList<String>();

        list.add("001");

        list.add("002");

        list.add("003");

        list.add("004");

        list.add("005");

        

        DelayQueue<JdkDelayImpl> queue = new DelayQueue<JdkDelayImpl>();

        long start = System.currentTimeMillis();

        for(int i = 0; i < 5; i++) {

            queue.put(new JdkDelayImpl(list.get(i), 

                    TimeUnit.NANOSECONDS.convert(3, TimeUnit.SECONDS)));

            try {

                queue.take().print();

                System.out.println("after: " + (System.currentTimeMillis() - start)

                        + " milliSeconds");

                

            } catch (Exception e) {

            }

        }

    }

}

 

3、基于netty方式，添加netty包

 

import java.util.concurrent.TimeUnit;

import io.netty.util.HashedWheelTimer;

import io.netty.util.Timeout;

import io.netty.util.Timer;

import io.netty.util.TimerTask;

public class NettyDeplayImpl {

    static class MyTimeTask implements TimerTask {

        boolean flag;

        

        public MyTimeTask(boolean flag) {

            this.flag = flag;

        }

        @Override

        public void run(Timeout arg0) throws Exception {

            System.out.println("going to delete order...");

            this.flag = false;

        }

    }

    

    public static void main(String[] args) {

        MyTimeTask timeTask = new MyTimeTask(true);

        Timer timer = new HashedWheelTimer();

        timer.newTimeout(timeTask, 5, TimeUnit.SECONDS);

        int i = 1;

        while(timeTask.flag) {

            try {

                Thread.sleep(1000);

            } catch (Exception e) {

            }

            System.err.println(i + " seconds gone");

            i++;

        }

    }

}

 

 


转载：https://www.cnblogs.com/codechange/p/8367208.html
java延迟队列，java高级面试笔试题
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