【一】自定义线程池

(1)为什么使用线程池
每一个线程的启动和结束都是比较消耗时间和占用资源的。使用线程池的过程中创建固定数量的线程,不用创建多余新的线程,而是循环使用那些已经存在的线程。

(2)自定义线程池设计思路
1-准备一个任务容器
2-一次性启动10个消费者线程
3-刚开始任务容器是空的,所以线程都wait在上面
4-直到一个外部线程往这个任务容器中扔了一个“任务”,就会有一个消费者线程被唤醒
5-这个消费者线程取出“任务”,并且执行这个任务,执行完毕后,继续等待下一次任务的到来
6-如果短时间内,有较多的任务加入,name就会有多个线程被唤醒,去执行这些任务

public class ThreadPool {
  
    // 线程池大小
    int threadPoolSize;
  
    // 任务容器
    LinkedList<Runnable> tasks = new LinkedList<Runnable>();
  
    // 试图消费任务的线程
  
    public ThreadPool() {
        threadPoolSize = 10;
  
        // 启动10个任务消费者线程
        synchronized (tasks) {
            for (int i = 0; i < threadPoolSize; i++) {
                new TaskConsumeThread("任务消费者线程 " + i).start();
            }
        }
    }
  
    public void add(Runnable r) {
        synchronized (tasks) {
            tasks.add(r);
            // 唤醒等待的任务消费者线程
            tasks.notifyAll();
        }
    }
  
    class TaskConsumeThread extends Thread {
        public TaskConsumeThread(String name) {
            super(name);
        }
  
        Runnable task;
  
        public void run() {
            System.out.println("启动: " + this.getName());
            while (true) {
                synchronized (tasks) {
                    while (tasks.isEmpty()) {
                        try {
                            tasks.wait();
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                    task = tasks.removeLast();
                    // 允许添加任务的线程可以继续添加任务
                    tasks.notifyAll();
  
                }
                System.out.println(this.getName() + " 获取到任务,并执行");
                task.run();
            }
        }
    }
  
}
public class TestThread {
       
    public static void main(String[] args) {
        ThreadPool pool = new ThreadPool();
  
        for (int i = 0; i < 5; i++) {
            Runnable task = new Runnable() {
                @Override
                public void run() {
                    //System.out.println("执行任务");
                    //任务可能是打印一句话
                    //可能是访问文件
                    //可能是做排序
                }
            };
             
            pool.add(task);
             
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
  
    }
           
}

【二】java自带的线程池

(1)线程池使用实例–使用java线程池实现穷举法破解密码

主要方法类

public class PassWordThreadpool {

    //第一步:把穷举法生成密码并且进行匹配的方法写好
    //如果匹配到密码了就停止遍历
    private boolean found = false;

    public synchronized void generatePwd(char[] guessPwd,String pwd, List<String> pwdList) {
        generatePwd(guessPwd,0,pwd, pwdList);
    }

    public synchronized void generatePwd(char[] guessPwd,int index,String pwd, List<String> pwdList) {
        //遍历数值和字母来生成密码
        if(found){
            return;
        }
        for (short i='0';i<'z';i++) {
            if(!Character.isLetterOrDigit(i)){
                continue;
            }
            char c = (char) i;
            guessPwd[index] = c;
            if(index==pwd.length()-1){
                //把三个字母的数组拼接成字符串
                String guessResult = new String(guessPwd);
                pwdList.add(guessResult);
                if(guessResult.equals(pwd)){
                    System.out.println("密码找到了,是:"+guessResult);
                    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                    System.out.println("当前时间是:"+df.format(new Date()));
                    found = true;
                    return;
                }
            } else {
                generatePwd(guessPwd,index+1,pwd, pwdList);
            }
        }
    }
}

线程池使用

public class TestThreadpoolGuesspwd {
    public static void main(String[] args) throws InterruptedException {

        String pwd = randomPwd(3);
        System.out.println("生成的密码是:"+pwd);
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        System.out.println("当前时间是:"+df.format(new Date()));
        List<String> pwdList = new CopyOnWriteArrayList<>();
        PassWordThreadpool passWordThread = new PassWordThreadpool();

        // 创建线程池
        ThreadPoolExecutor threadPool= new ThreadPoolExecutor(10, 15, 60, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

        // 把任务提交到线程池
        threadPool.execute(() -> {
            char[] guessPwd = new char[pwd.length()];
            passWordThread.generatePwd(guessPwd,pwd, pwdList);
        });

    }

    public static String randomPwd(int length) {
        String pool = "";
        for (short i = '0'; i <= '9'; i++) {
            pool += (char) i;
        }
        for (short i = 'a'; i <= 'z'; i++) {
            pool += (char) i;
        }
        for (short i = 'A'; i <= 'Z'; i++) {
            pool += (char) i;
        }
        char cs[] = new char[length];
        for (int i = 0; i < cs.length; i++) {
            int index = (int) (Math.random() * pool.length());
            cs[i] = pool.charAt(index);
        }
        String result = new String(cs);
        return result;
    }
}

【三】如何优雅的等待线程池所有任务执行完

(1)案例一:主线程在子线程结束前先结束了

public class TestThreadpoolImport01 {

    private static ThreadPoolExecutor executor = new ThreadPoolExecutor(0,25,100L,
            TimeUnit.SECONDS,new LinkedBlockingQueue<>(),new ThreadPoolExecutor.CallerRunsPolicy());
    public static void main(String[] args) {
        Student student = null;
        List<Student> studentList = new ArrayList<>();
        int age = 0;
        int heigh = 0;
        //添加50万个数据
        for (int i=0;i<=500000;i++) {
            age = (int) Math.floor((Math.random() * 10) + 20);
            heigh = (int) Math.floor((Math.random() * 160) + 180);
            student = new Student("name"+i,age,heigh,"玩");
            studentList.add(student);
        }

        long start = System.currentTimeMillis();
        for (Student student1:studentList) {
            //模拟对数据信息进行二次处理
            executor.submit(()->student1.setName(student1.getName()+"这是后缀"));
        }
        long end = System.currentTimeMillis();
        System.out.println("添加数量:"+studentList.stream().filter(x->x.getName().contains("这是后缀")).count());
        System.out.println("花费时间:"+(end-start));


        //输出的数据是
        // 添加数量:371014
        // 花费时间:114
        //不是50w,这是由于线程池中的子线程任务没有执行完,而主线程已经开始执行业务代码,导致成功数量变少。

    }
}

以前在没有使用线程池之前,可以将所有线程放进线程数组,然后遍历数组,给每个线程对象调用join方法,现在来探索线程池的如何实现

(2)案例二:使用CountDownLatch

public class TestThreadpoolImport02 {

    private static ThreadPoolExecutor executor = new ThreadPoolExecutor(0,25,100L,
            TimeUnit.SECONDS,new LinkedBlockingQueue<>(),new ThreadPoolExecutor.CallerRunsPolicy());
    public static void main(String[] args) {
        Student student = null;
        List<Student> studentList = new ArrayList<>();
        int age = 0;
        int heigh = 0;
        //添加50万个数据
        for (int i=0;i<500000;i++) {
            age = (int) Math.floor((Math.random() * 10) + 20);
            heigh = (int) Math.floor((Math.random() * 160) + 180);
            student = new Student("name"+i,age,heigh,"玩");
            studentList.add(student);
        }

        long start = System.currentTimeMillis();

        //在线程池执行之前,给计数器指定数值(与要执行代码的次数一致)也就是students.size()
        CountDownLatch countDownLatch = new CountDownLatch(studentList.size());

        for (Student student1:studentList) {
            //模拟对数据信息进行二次处理
            executor.submit(()->{
                try {
                    student1.setName(student1.getName()+"这是后缀");
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    //每执行一次数值减少一
                    countDownLatch.countDown();
                    //也可以给await()设置超时时间,如果超过300s(也可以是时,分)则不再等待,直接执行下面代码。
                    //countDownLatch.await(300,TimeUnit.SECONDS);
                }
            });
        }
        try {
            //等待计数器归零
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        long end = System.currentTimeMillis();
        System.out.println("添加数量:"+studentList.stream().filter(x->x.getName().contains("这是后缀")).count());
        System.out.println("花费时间:"+(end-start));


        //输出的数据是
        // 添加数量:500000
        // 花费时间:334
        //是50w,主线程等待所有子线程执行结束后才结束

    }
}

这是一个计数器操作,在线程池执行之前,给计数器指定数值(与要执行代码的次数一致)也就是students.size(),在线程池执行代码体里面要加上countDownLatch.countDown();代表每执行一次数值减少一,最后在循环体外边写上countDownLatch.await();代表等待计数器归零。

也可以给await()设置超时时间。如果超过300s(也可以是时,分)则不再等待,直接执行下面代码。

countDownLatch.await(300,TimeUnit.SECONDS);

(3)使用Future.get()

public class TestThreadpoolImport03 {

    private static ThreadPoolExecutor executor = new ThreadPoolExecutor(0,25,100L,
            TimeUnit.SECONDS,new LinkedBlockingQueue<>(),new ThreadPoolExecutor.CallerRunsPolicy());
    public static void main(String[] args) {
        Student student = null;
        List<Student> studentList = new ArrayList<>();
        int age = 0;
        int heigh = 0;
        //添加50万个数据
        for (int i=0;i<500000;i++) {
            age = (int) Math.floor((Math.random() * 10) + 20);
            heigh = (int) Math.floor((Math.random() * 160) + 180);
            student = new Student("name"+i,age,heigh,"玩");
            studentList.add(student);
        }

        long start = System.currentTimeMillis();

        List<Future> futureList = new ArrayList<>();

        for (Student student1:studentList) {
            //使用submit提交会有一个返回值
            Future future = executor.submit(()->{
                try {
                    //模拟对数据信息进行二次处理
                    student1.setName(student1.getName()+"这是后缀");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
            futureList.add(future);
        }

        for (Future future:futureList) {
            try {
                //监听线程池子线程执行状态及执行结果。
                future.get();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }

        long end = System.currentTimeMillis();
        System.out.println("添加数量:"+studentList.stream().filter(x->x.getName().contains("这是后缀")).count());
        System.out.println("花费时间:"+(end-start));


        //输出的数据是
        // 添加数量:500000
        // 花费时间:334
        //是50w,主线程等待所有子线程执行结束后才结束

    }
}

使用submit提交线程,会返回一个Future的值,将每个返回值放进List,然后遍历调用get方法:future.get();

(4)使用shutdown方法
如果线程池是方法内部创建的,可以直接使用shutdown()也会等待线程池的执行结果。同时会关闭线程池资源。

public class TestThreadpoolImport04 {

    public static void main(String[] args) {
        ThreadPoolExecutor executor = new ThreadPoolExecutor(0,25,100L,
                TimeUnit.SECONDS,new LinkedBlockingQueue<>(),new ThreadPoolExecutor.CallerRunsPolicy());

        Student student = null;
        List<Student> studentList = new ArrayList<>();
        int age = 0;
        int heigh = 0;
        //添加50万个数据
        for (int i=0;i<500000;i++) {
            age = (int) Math.floor((Math.random() * 10) + 20);
            heigh = (int) Math.floor((Math.random() * 160) + 180);
            student = new Student("name"+i,age,heigh,"玩");
            studentList.add(student);
        }

        long start = System.currentTimeMillis();
        for (Student student1:studentList) {
            //模拟对数据信息进行二次处理
            executor.submit(()->student1.setName(student1.getName()+"这是后缀"));
        }
        executor.shutdown();
        try {
            executor.awaitTermination(300,TimeUnit.SECONDS);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        long end = System.currentTimeMillis();
        System.out.println("添加数量:"+studentList.stream().filter(x->x.getName().contains("这是后缀")).count());
        System.out.println("花费时间:"+(end-start));


        //输出的数据是
        // 添加数量:500000
        // 花费时间:281
        //不是50w,这是由于线程池中的子线程任务没有执行完,而主线程已经开始执行业务代码,导致成功数量变少。

    }
}

【四】如何优雅的关闭线程池

【五】案例一:用线程池异步查询订单和收货地址

(1)使用两个不同的线程分别查询订单和收货地址

/**
 * @ClassName: TestThreadSearch
 * @Author: AllenSun
 * @Date: 2022/3/21 下午10:57
 */
public class TestThreadSearch {

    public static void getOrder() {
        try {
            Thread.sleep(1000);
            System.out.println("获取订单信息");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void getAddress() {
        try {
            Thread.sleep(1000);
            System.out.println("获取地址信息");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        getOrder();
        getAddress();
        long end = System.currentTimeMillis();
        //花费时间:2007
        System.out.println("花费时间:"+(end-start));

    }
}

耗时结果为

获取订单信息
获取地址信息
花费时间:2008

Process finished with exit code 0

(2)使用线程池改造

/**
 * @ClassName: TestThreadSearch
 * @Author: AllenSun
 * @Date: 2022/3/21 下午10:57
 */
public class TestThreadPoolSearch {

    public static void getOrder() {
        try {
            Thread.sleep(1000);
            System.out.println("获取订单信息");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void getAddress() {
        try {
            Thread.sleep(1000);
            System.out.println("获取地址信息");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {

        ThreadPoolExecutor executor= new ThreadPoolExecutor(
                5,
                10,
                15,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<Runnable>()
        );

        long start = System.currentTimeMillis();
        //异步执行
        CompletableFuture<Void> addressFuture = CompletableFuture.runAsync(()->{
            getAddress();
        },executor);
        //异步执行
        CompletableFuture<Void> orderFuture = CompletableFuture.runAsync(()->{
            getOrder();
        },executor);

        //等待完成
        CompletableFuture.allOf(addressFuture,orderFuture).get();


        long end = System.currentTimeMillis();

        //花费时间:1053
        System.out.println("花费时间:"+(end-start));

        executor.shutdown();

    }
}

耗时结果为

获取地址信息
获取订单信息
花费时间:1127

Process finished with exit code 0

(3)使用线程池改造

/**
 * @ClassName: TestThreadSearch
 * @Author: AllenSun
 * @Date: 2022/3/21 下午10:57
 */
public class TestThreadPoolSearch2 {
    private static final CountDownLatch ctl = new CountDownLatch(2);
    
    public static void getOrder() {
        try {
            Thread.sleep(1000);
            System.out.println("获取订单信息");
            ctl.countDown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void getAddress() {
        try {
            Thread.sleep(1000);
            System.out.println("获取地址信息");
            ctl.countDown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {

        ThreadPoolExecutor executor= new ThreadPoolExecutor(
                5,
                10,
                15,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<Runnable>()
        );

        long start = System.currentTimeMillis();
        //异步执行
        executor.execute(() -> {
            getOrder();
        });
        executor.execute(() -> {
            getAddress();
        });

        //等待完成
        try {
            //等待计数器归零
            ctl.await(20, TimeUnit.SECONDS);//最多等待20秒,不管子线程完没完
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        

        long end = System.currentTimeMillis();

        //花费时间:1053
        System.out.println("花费时间:"+(end-start));

        executor.shutdown();

    }
}

耗时结果为

获取地址信息
获取订单信息
花费时间:1100

Process finished with exit code 0

【六】案例二:线程池模拟批量导入数据

public class TestThreadpoolImport02 {

    private static ThreadPoolExecutor executor = new ThreadPoolExecutor(0,25,100L,
            TimeUnit.SECONDS,new LinkedBlockingQueue<>(),new ThreadPoolExecutor.CallerRunsPolicy());
    public static void main(String[] args) {
        Student student = null;
        List<Student> studentList = new ArrayList<>();
        int age = 0;
        int heigh = 0;
        //添加50万个数据
        for (int i=0;i<500000;i++) {
            age = (int) Math.floor((Math.random() * 10) + 20);
            heigh = (int) Math.floor((Math.random() * 160) + 180);
            student = new Student("name"+i,age,heigh,"玩");
            studentList.add(student);
        }

        long start = System.currentTimeMillis();

        //在线程池执行之前,给计数器指定数值(与要执行代码的次数一致)也就是students.size()
        CountDownLatch countDownLatch = new CountDownLatch(studentList.size());

        for (Student student1:studentList) {
            //模拟对数据信息进行二次处理
            executor.submit(()->{
                try {
                    student1.setName(student1.getName()+"这是后缀");
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    //每执行一次数值减少一
                    countDownLatch.countDown();
                    //也可以给await()设置超时时间,如果超过300s(也可以是时,分)则不再等待,直接执行下面代码。
                    //countDownLatch.await(300,TimeUnit.SECONDS);
                }
            });
        }
        try {
            //等待计数器归零
            countDownLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        long end = System.currentTimeMillis();
        System.out.println("添加数量:"+studentList.stream().filter(x->x.getName().contains("这是后缀")).count());
        System.out.println("花费时间:"+(end-start));


        //输出的数据是
        // 添加数量:500000
        // 花费时间:334
        //是50w,主线程等待所有子线程执行结束后才结束

    }
}
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