一、重要参数
corePollSize：核心线程数。在创建了线程池后，线程中没有任何线程，等到有任务到来时才创建线程去执行任务。
maximumPoolSize：最大线程数。表明线程中最多能够创建的线程数量。
keepAliveTime：空闲的线程保留的时间。
TimeUnit：空闲线程的保留时间单位。
BlockingQueue：阻塞队列，存储等待执行的任务。参数有ArrayBlockingQueue、LinkedBlockingQueue、SynchronousQueue可选。
ThreadFactory：线程工厂，用来创建线程
RejectedExecutionHandler：队列已满，而且任务量大于最大线程的异常处理策略。
ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。
ThreadPoolExecutor.DiscardPolicy：也是丢弃任务，但是不抛出异常。
ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面的任务，然后重新尝试执行任务（重复此过程）
ThreadPoolExecutor.CallerRunsPolicy：由调用线程处理该任务
二、四类构造函数
1、 ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue)
2、ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler)
3、 ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory)
4、 ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler)
三、实现线程池的四种策略
1、newCachedThreadPool
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.
MAX_VALUE,
60L, TimeUnit.
SECONDS,
new SynchronousQueue<Runnable>());
}
2、newFixedThreadPool
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.
MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
3、newSingleThreadExecutor
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
( new ThreadPoolExecutor(1, 1,
0L, TimeUnit.
MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
4、newScheduledThreadPool
public static ScheduledExecutorService newScheduledThreadPool (int corePoolSize) {
return new ScheduledThreadPoolExecutor(corePoolSize);
}
public ScheduledThreadPoolExecutor( int corePoolSize) {
super(corePoolSize, Integer.
MAX_VALUE, 0, TimeUnit.
NANOSECONDS,
new DelayedWorkQueue());
}