创建线程池的三种方法自定义线程池拒绝策略( 二 )

public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize,long keepAliveTime, TimeUnit unit,BlockingQueue<Runnable> workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler) {if (corePoolSize < 0 ||maximumPoolSize <= 0 ||maximumPoolSize < corePoolSize ||keepAliveTime < 0)throw new IllegalArgumentException();if (workQueue == null || threadFactory == null || handler == null)throw new NullPointerException();this.acc = System.getSecurityManager() == null ?null :AccessController.getContext();this.corePoolSize = corePoolSize;this.maximumPoolSize = maximumPoolSize;this.workQueue = workQueue;this.keepAliveTime = unit.toNanos(keepAliveTime);this.threadFactory = threadFactory;this.handler = handler;}关于此构造方法中各参数的含义和作用，各位可以移步《高并发之——不得不说的线程池与ThreadPoolExecutor类浅析》进行查阅。
大家可以自行调用ThreadPoolExecutor类的构造方法来创建线程池。例如，我们可以使用如下形式创建线程池。
new ThreadPoolExecutor(0, Integer.MAX_VALUE,60L, TimeUnit.SECONDS,new SynchronousQueue<Runnable>());使用ForkJoinPool类创建线程池在Java8的Executors工具类中，新增了如下创建线程池的方式。
public static ExecutorService newWorkStealingPool(int parallelism) {return new ForkJoinPool(parallelism, ForkJoinPool.defaultForkJoinWorkerThreadFactory, null, true);}public static ExecutorService newWorkStealingPool() {return new ForkJoinPool(Runtime.getRuntime().availableProcessors(), ForkJoinPool.defaultForkJoinWorkerThreadFactory, null, true);}从源代码可以可以，本质上调用的是ForkJoinPool类的构造方法类创建线程池，而从代码结构上来看ForkJoinPool类继承自AbstractExecutorService抽象类。接下来，我们看下ForkJoinPool类的构造方法。
public ForkJoinPool() {this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()), defaultForkJoinWorkerThreadFactory, null, false);} public ForkJoinPool(int parallelism) {this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);}public ForkJoinPool(int parallelism,ForkJoinWorkerThreadFactory factory,UncaughtExceptionHandler handler,boolean asyncMode) {this(checkParallelism(parallelism), checkFactory(factory), handler, asyncMode ? FIFO_QUEUE : LIFO_QUEUE, "ForkJoinPool-" + nextPoolId() + "-worker-");checkPermission();}private ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory, UncaughtExceptionHandler handler, int mode, String workerNamePrefix) {this.workerNamePrefix = workerNamePrefix;this.factory = factory;this.ueh = handler;this.config = (parallelism & SMASK) | mode;long np = (long)(-parallelism); // offset ctl countsthis.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);}通过查看源代码得知，ForkJoinPool的构造方法，最终调用的是如下私有构造方法。
private ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory, UncaughtExceptionHandler handler, int mode, String workerNamePrefix) {this.workerNamePrefix = workerNamePrefix;this.factory = factory;this.ueh = handler;this.config = (parallelism & SMASK) | mode;long np = (long)(-parallelism); // offset ctl countsthis.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);}其中，各参数的含义如下所示。
parallelism：并发级别。factory：创建线程的工厂类对象。handler：当线程池中的线程抛出未捕获的异常时，统一使用UncaughtExceptionHandler对象处理。mode：取值为FIFO_QUEUE或者LIFO_QUEUE 。workerNamePrefix：执行任务的线程名称的前缀。当然，私有构造方法虽然是参数最多的一个方法，但是其不会直接对外方法，我们可以使用如下方式创建线程池。
new ForkJoinPool();new ForkJoinPool(Runtime.getRuntime().availableProcessors());new ForkJoinPool(Runtime.getRuntime().availableProcessors(),ForkJoinPool.defaultForkJoinWorkerThreadFactory,null, true);使用ScheduledThreadPoolExecutor类创建线程池在Executors工具类中存在如下方法类创建线程池。

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创建线程池的三种方法 自定义线程池拒绝策略( 二 )

创建线程池的三种方法自定义线程池拒绝策略( 二 )