摘要：
1.介绍当线程池线程数大于最大线程数时，多余的任务，程序应该按照什么拒绝策略处理。
1.介绍
当线程池线程数大于最大线程数（maximumPoolSize）时，多余的任务，程序应该按照什么拒绝策略处理。
2.拒绝策略4个
AbortPolicy：丢弃任务，并抛出RejectedExecutionException异常（需要在调用线程处捕获异常，即执行submit线程处）
DiscardPolicy：丢弃任务，不抛出异常
DiscardOldestPolicy：丢弃等待队列最前面任务
CallerRunsPolicy：由调用线程处理该任务
3.示例
3.1.AbortPolicy捕获异常
public classRejectedAbortPolicy { static classMyRunnable implements Runnable { privateString jobName; MyRunnable(String jobName) { this.jobName =jobName; } @Override public voidrun() { try{ while (true) { Thread.currentThread(); Thread.sleep(1000); System.err.println("当前线程：" + Thread.currentThread().getName() + "当前任务：" +jobName); } } catch(InterruptedException e) { //TODO Auto-generated catch block e.printStackTrace(); } } } public static voidmain(String[] args) throws InterruptedException { ExecutorService es = new ThreadPoolExecutor(2, 2, 0, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(1), Executors.defaultThreadFactory(), newAbortPolicy()); es.submit(new MyRunnable("job-1")); es.submit(new MyRunnable("job-2")); es.submit(new MyRunnable("job-3")); Thread.sleep(5000); try{ Future<?> f = es.submit(new MyRunnable("job-4")); f.get();//这一句永远执行不到 } catch(Exception e) { System.err.println("job-4 submit Thread pool mistake"); } } }
3.2.DiscardOldestPolicy测试丢弃等待队列最前面任务
public classRejectedDiscardOldestPolicy { static classMyRunnable implements Runnable { privateString jobName; MyRunnable(String jobName) { this.jobName =jobName; } publicString getJobName(){ returnjobName; } @Override public voidrun() { try{ while (true) { Thread.currentThread(); Thread.sleep(1000); System.err.println("当前线程：" + Thread.currentThread().getName() + "当前任务：" +jobName); } } catch(InterruptedException e) { //TODO Auto-generated catch block e.printStackTrace(); } } } public static voidmain(String[] args) throws InterruptedException { BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<Runnable>(1); ExecutorService es = new ThreadPoolExecutor(2, 2, 0, TimeUnit.SECONDS, workQueue, Executors.defaultThreadFactory(), newThreadPoolExecutor.DiscardOldestPolicy()); es.execute(new MyRunnable("job-1")); es.execute(new MyRunnable("job-2")); es.execute(new MyRunnable("job-3")); Runnable firstRunnable =workQueue.poll(); System.err.println("submit job-3 检查队列当前 Runnable名称:" +((MyRunnable) firstRunnable).getJobName()); workQueue.add(firstRunnable); Thread.sleep(5000); es.execute(new MyRunnable("job-4")); Runnable SecondRunnable =workQueue.poll(); System.err.println("submit job-4 检查队列当前 Runnable名称应该为job-4，实际为:" +((MyRunnable) SecondRunnable).getJobName()); workQueue.add(SecondRunnable); } }
3.3.CallerRunsPolicy主线程处理这个任务
public classRejectedCallerRunsPolicy { static classMyRunnable implements Runnable { privateString jobName; MyRunnable(String jobName) { this.jobName =jobName; } publicString getJobName(){ returnjobName; } @Override public voidrun() { try{ while (true) { Thread.currentThread(); Thread.sleep(1000); System.err.println("当前线程：" + Thread.currentThread().getName() + "当前任务：" +jobName); } } catch(InterruptedException e) { //TODO Auto-generated catch block e.printStackTrace(); } } } public static voidmain(String[] args) throws InterruptedException { BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<Runnable>(1); ExecutorService es = new ThreadPoolExecutor(2, 2, 0, TimeUnit.SECONDS, workQueue, Executors.defaultThreadFactory(), newThreadPoolExecutor.CallerRunsPolicy()); es.execute(new MyRunnable("job-1")); es.execute(new MyRunnable("job-2")); es.execute(new MyRunnable("job-3")); Thread.sleep(5000); es.execute(new MyRunnable("job-4")); } }