//创建单一线程
 ExecutorService executorService= Executors.newSingleThreadExecutor();
 //创建可伸缩线程
 ExecutorService executorService1=Executors.newCachedThreadPool();
 //指定创建3个线程
 ExecutorService executorService2=Executors.newFixedThreadPool(3);

一般不会用newCachedThreadPool太耗费内存，而newSingleThreadExecutor和newFixedThreadPool

容易积累大量的oom异常

用工具类创建线程池_hh