java 个人札记

Executor

Executor

用于提交任务，Executor将线程的创建与执行机制进行解偶

public interface Executor {    void execute(Runnable command);}

我们定义一个任务，然后自己创建线程去执行任务，这样线程的创建就与任务执行产生了耦和。

public class ExecutorTest {    public static void main(String[] args) {        Thread thread = new Thread(new MyRunnable());        thread.start();    }    static class MyRunnable implements Runnable {        @Override        public void run() {            System.out.println("执行我的任务");        }    }}输出：执行我的任务

使用Executor，我们只需要创建任务，然后由Executor代替我们去创建线程去执行任务。

public class ExecutorTest {    public static void main(String[] args) {        new TaskExecutor().execute(new MyRunnable());    }    static class MyRunnable implements Runnable {        @Override        public void run() {            System.out.println("执行我的任务");        }    }    static class TaskExecutor implements Executor{        @Override        public void execute(Runnable command) {            new Thread(command).start();        }    }}输出：执行我的任务

但是Executor并不严格要求任务执行是异步的（大多数情况是异步执行），Executor可以在当前线程立即执行任务，比如：

public class DirectExecutor implements Executor {    public void execute(Runnable r) {      r.run();    } }

ThreadFactory

而Executor通常也不是自己去创建线程，而是通过线程工厂来进行创建线程，比如ThreadPerTaskExecutor组合了一个线程工厂，把线程的创建交给线程工厂

public final class ThreadPerTaskExecutor implements Executor {    private final ThreadFactory threadFactory;    public ThreadPerTaskExecutor(ThreadFactory threadFactory) {        if (threadFactory == null) {            throw new NullPointerException("threadFactory");        } else {            this.threadFactory = threadFactory;        }    }    public void execute(Runnable command) {        this.threadFactory.newThread(command).start();    }}

通过ThreadFactory创建线程，ThreadFactory不仅仅是创建线程，还会设置线程组、线程的名字、线程的优先级等等

static class DefaultThreadFactory implements ThreadFactory {        private static final AtomicInteger poolNumber = new AtomicInteger(1);        private final ThreadGroup group;        private final AtomicInteger threadNumber = new AtomicInteger(1);        private final String namePrefix;        DefaultThreadFactory() {            SecurityManager s = System.getSecurityManager();            group = (s != null) ? s.getThreadGroup() :                                  Thread.currentThread().getThreadGroup();            namePrefix = "pool-" +                          poolNumber.getAndIncrement() +                         "-thread-";        }        public Thread newThread(Runnable r) {            Thread t = new Thread(group, r,                                  namePrefix + threadNumber.getAndIncrement(),                                  0);            if (t.isDaemon())                t.setDaemon(false);            if (t.getPriority() != Thread.NORM_PRIORITY)                t.setPriority(Thread.NORM_PRIORITY);            return t;        }    }