线程遇到未解决的异样就完结了
这个好了解，当线程呈现未捕捉异样的时候就执行不上来了，留给它的就是垃圾回收了。
线程池中线程频繁呈现未捕捉异样
当线程池中线程频繁呈现未捕捉的异样，那线程的复用率就大大降低了，须要一直地创立新线程。
做个试验：
public class ThreadExecutor { private ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 1, 60, TimeUnit.SECONDS, new ArrayBlockingQueue<>(200), new ThreadFactoryBuilder().setNameFormat("customThread %d").build()); @Test public void test() { IntStream.rangeClosed(1, 5).forEach(i -> { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } threadPoolExecutor.execute(() -> { int j = 1/0; });}); }}新建一个只有一个线程的线程池，每隔0.1s提交一个工作，工作中是一个1/0的计算。
Exception in thread "customThread 0" java.lang.ArithmeticException: / by zero at thread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)Exception in thread "customThread 1" java.lang.ArithmeticException: / by zero at thread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)Exception in thread "customThread 2" java.lang.ArithmeticException: / by zero at thread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)Exception in thread "customThread 3" java.lang.ArithmeticException: / by zero at thread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)Exception in thread "customThread 4" java.lang.ArithmeticException: / by zero at thread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)Exception in thread "customThread 5" java.lang.ArithmeticException: / by zero at thread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)可见每次执行的线程都不一样，之前的线程都没有复用。起因是因为呈现了未捕捉的异样。
咱们把异样捕捉试试：
public class ThreadExecutor { private ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 1, 60, TimeUnit.SECONDS, new ArrayBlockingQueue<>(200), new ThreadFactoryBuilder().setNameFormat("customThread %d").build()); @Test public void test() { IntStream.rangeClosed(1, 5).forEach(i -> { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } threadPoolExecutor.execute(() -> { try { int j = 1 / 0; } catch (Exception e) { System.out.println(Thread.currentThread().getName() +" "+ e.getMessage()); } }); }); }}customThread 0 / by zerocustomThread 0 / by zerocustomThread 0 / by zerocustomThread 0 / by zerocustomThread 0 / by zero可见当异样捕捉了，线程就能够复用了。
问题来了，咱们的代码中异样不可能全副捕捉
如果要捕捉那些没被业务代码捕捉的异样，能够设置Thread类的uncaughtExceptionHandler属性。这时应用ThreadFactoryBuilder会比拟不便，ThreadFactoryBuilder是guava提供的ThreadFactory生成器。
new ThreadFactoryBuilder().setNameFormat("customThread %d").setUncaughtExceptionHandler((t, e) -> System.out.println(t.getName() + "产生异样" + e.getCause())).build()批改之后：
public class ThreadExecutor { private static ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 1, 60, TimeUnit.SECONDS, new ArrayBlockingQueue<>(200), new ThreadFactoryBuilder() .setNameFormat("customThread %d") .setUncaughtExceptionHandler((t, e) -> System.out.println("UncaughtExceptionHandler捕捉到：" + t.getName() + "产生异样" + e.getMessage())) .build()); @Test public void test() { IntStream.rangeClosed(1, 5).forEach(i -> { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } threadPoolExecutor.execute(() -> { System.out.println("线程" + Thread.currentThread().getName() + "执行"); int j = 1 / 0; }); }); }}线程customThread 0执行UncaughtExceptionHandler捕捉到：customThread 0产生异样/ by zero线程customThread 1执行UncaughtExceptionHandler捕捉到：customThread 1产生异样/ by zero线程customThread 2执行UncaughtExceptionHandler捕捉到：customThread 2产生异样/ by zero线程customThread 3执行UncaughtExceptionHandler捕捉到：customThread 3产生异样/ by zero线程customThread 4执行UncaughtExceptionHandler捕捉到：customThread 4产生异样/ by zero可见，后果并不是咱们设想的那样，线程池中原有的线程没有复用！所以通过UncaughtExceptionHandler想将异样吞掉使线程复用这招貌似行不通。它只是做了一层异样的保底解决。
将excute改成submit试试
public class ThreadExecutor { private static ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 1, 60, TimeUnit.SECONDS, new ArrayBlockingQueue<>(200), new ThreadFactoryBuilder() .setNameFormat("customThread %d") .setUncaughtExceptionHandler((t, e) -> System.out.println("UncaughtExceptionHandler捕捉到：" + t.getName() + "产生异样" + e.getMessage())) .build()); @Test public void test() { IntStream.rangeClosed(1, 5).forEach(i -> { try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } Future<?> future = threadPoolExecutor.submit(() -> { System.out.println("线程" + Thread.currentThread().getName() + "执行"); int j = 1 / 0; }); try { future.get(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } }); }}线程customThread 0执行java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero线程customThread 0执行java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero线程customThread 0执行java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero线程customThread 0执行java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero线程customThread 0执行java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero通过submit提交线程能够屏蔽线程中产生的异样，达到线程复用。当get()执行后果时异样才会抛出。
起因是通过submit提交的线程，当产生异样时，会将异样保留，待future.get();时才会抛出。
这是Futuretask的局部run()办法，看setException：
public void run() { try { Callable<V> c = callable; if (c != null && state == NEW) { V result; boolean ran; try { result = c.call(); ran = true; } catch (Throwable ex) { result = null; ran = false; setException(ex); } if (ran) set(result); } } }protected void setException(Throwable t) { if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) { outcome = t; UNSAFE.putOrderedInt(this, stateOffset, EXCEPTIONAL); // final state finishCompletion(); }}将异样存在outcome对象中，没有抛出，再看get办法：
public V get() throws InterruptedException, ExecutionException { int s = state; if (s <= COMPLETING) s = awaitDone(false, 0L); return report(s);}private V report(int s) throws ExecutionException { Object x = outcome; if (s == NORMAL) return (V)x; if (s >= CANCELLED) throw new CancellationException(); throw new ExecutionException((Throwable)x);}当outcome是异样时才抛出。
总结
1、线程池中线程中异样尽量手动捕捉
2、通过设置ThreadFactory的UncaughtExceptionHandler能够对未捕捉的异样做保底解决，通过execute提交工作，线程仍然会中断，而通过submit提交工作，能够获取线程执行后果，线程异样会在get执行后果时抛出。
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