文章目录
前言
对于Java的InterceptException以及interrupt()等方法总会有疑惑，或者记不清，其实最好的解释就是方法的doc注释
一、interrupt()
咱们看看源码上，对于interrupt()方法的注释：
/**
* Interrupts this thread.
*
* <p> Unless the current thread is interrupting itself, which is
* always permitted, the {@link #checkAccess() checkAccess} method
* of this thread is invoked, which may cause a {@link
* SecurityException} to be thrown.
* 除非是当前线程的自我中断，当然这是允许的，否则会调用线程的checkAccess方法来判断调用方是否有权限做此次更改，
* 所以该方法可能会抛出SecurityException
*
* <p> If this thread is blocked in an invocation of the {@link
* Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
* Object#wait(long, int) wait(long, int)} methods of the {@link Object}
* class, or of the {@link #join()}, {@link #join(long)}, {@link
* #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
* methods of this class, then its interrupt status will be cleared and it
* will receive an {@link InterruptedException}.
* 如果此线程阻塞在Object的wait()、或者Thread的join()、sleep()方法上，那么该线程的中断状态将会被清空，
* 并且会得到InterruptedException
*
* <p> If this thread is blocked in an I/O operation upon an {@link
* java.nio.channels.InterruptibleChannel InterruptibleChannel}
* then the channel will be closed, the thread's interrupt
* status will be set, and the thread will receive a {@link
* java.nio.channels.ClosedByInterruptException}.
* 如果此线程阻塞在InterruptibleChannel的I/O操作上，那么这个InterruptibleChannel将会被关闭，同时
* 设置该线程的中断状态，并且会得到ClosedByInterruptException
*
* <p> If this thread is blocked in a {@link java.nio.channels.Selector}
* then the thread's interrupt status will be set and it will return
* immediately from the selection operation, possibly with a non-zero
* value, just as if the selector's {@link
* java.nio.channels.Selector#wakeup wakeup} method were invoked.
* 如果此线程阻塞在多路复用器上，设置该线程的中断状态，并且从多路复用器的select方法立马返回，也许会是一个非零值，
* 方法调用接口类似于调用了Selector#wakeup方法
*
* <p> If none of the previous conditions hold then this thread's interrupt
* status will be set. </p>
* 除了上面这些情况，那么就会设置下线程的中断状态
*
* <p> Interrupting a thread that is not alive need not have any effect.
* 如果一个线程的状态已经不是alive了，那么中断该线程不会有任何影响
*
* @throws SecurityException
* if the current thread cannot modify this thread
*
* @revised 6.0
* @spec JSR-51
*/
public void interrupt() {
if (this != Thread.currentThread())
checkAccess();
synchronized (blockerLock) {
Interruptible b = blocker;
if (b != null) {
interrupt0(); // Just to set the interrupt flag
b.interrupt(this);
return;
}
}
interrupt0();
}
所以根据上面的注释可以看到，如果线程被非自己调用了interrupt方法的话，主要是下面的情况：
1. 线程阻塞在Object#wait()、或者Thread#join()、Thread#sleep()方法上：清除中断状态，得到InterruptedException，当然得到的InterruptedException也会往上抛。所以Object#wait()、或者Thread#join()、Thread#sleep()都会抛出InterruptedException
2. 线程阻塞在InterruptibleChannel的I/O操作上：那么该通道就会被关闭，设置该线程的中断状态，同时抛出ClosedByInterruptException。举个例子，譬如你在调用FileChannel#transferTo时，当数据还没传输完成，对该线程调用了interrupt方法，那么该线程会抛出ClosedByInterruptException
3. 如果此线程阻塞在多路复用器Selector上：设置该线程的中断状态，并且从多路复用器的select方法立马返回，也许会是一个非零值，方法调用接口类似于调用了Selector#wakeup方法。就是说如果当Selector#select()方法在调用，但是还没返回时，对线程调用了interrupt方法，那么其效果类似于，设置了中断状态，并调用了Selector#wakeup
4. 其他情况：设置中断状态
所以判断一个线程是否被中断，其实可以看看线程是否抛出了InterruptedException或者抛出ClosedByInterruptException或者其中断状态被设置了。
二、interrupted()和isInterrupted()
1.interrupted()
/**
* Tests whether the current thread has been interrupted. The
* <i>interrupted status</i> of the thread is cleared by this method. In
* other words, if this method were to be called twice in succession, the
* second call would return false (unless the current thread were
* interrupted again, after the first call had cleared its interrupted
* status and before the second call had examined it).
* 判断当前线程是否被中断：该方法会清除中断状态
*
* <p>A thread interruption ignored because a thread was not alive
* at the time of the interrupt will be reflected by this method
* returning false.
*
* @return <code>true</code> if the current thread has been interrupted;
* <code>false</code> otherwise.
* @see #isInterrupted()
* @revised 6.0
*/
public static boolean interrupted() {
return currentThread().isInterrupted(true);
}
可以看到interrupted()方法是Thread类的静态方法，方法注释写了，该方法在判断线程是否被中断的同时，会清除掉中断状态
2. isInterrupted()
/**
* Tests whether this thread has been interrupted. The <i>interrupted
* status</i> of the thread is unaffected by this method.
* 判断当前线程是否被中断：中断状态不会被清除
*
* <p>A thread interruption ignored because a thread was not alive
* at the time of the interrupt will be reflected by this method
* returning false.
*
* @return <code>true</code> if this thread has been interrupted;
* <code>false</code> otherwise.
* @see #interrupted()
* @revised 6.0
*/
public boolean isInterrupted() {
return isInterrupted(false);
}
可以看到isInterrupted()方法是Thread类的成员方法，方法注释写了，该方法在判断线程是否被中断的同时，不会对中断状态进行任何影响。
3. isInterrupted(boolean ClearInterrupted)
/**
* Tests if some Thread has been interrupted. The interrupted state
* is reset or not based on the value of ClearInterrupted that is
* passed.
*/
private native boolean isInterrupted(boolean ClearInterrupted);
代码如下（示例）：
其实可以看到不管是interrupted方法还是isInterrupted()方法，调用的其实是Thread类里private的isInterrupted(boolean ClearInterrupted)方法，入参就是是否清楚中断状态，因为是native方法，就不再继续深入。
总结
- 如何判断一个线程是否被中断：
2. 可以看线程是否抛出了InterruptedException
3. 可以看线程是否抛出ClosedByInterruptException
4. 可以判断线程的中断状态是否被设置了
- 通过interrupted和isInterrupted来读取中断状态判断线程是否被中断了区别
6. interrupted会清除中断状态，isInterrupted不会清除中断状态；所以对于同一次的interrupt，interrupted只有第一次调用会返回true，而isInterrupted会一直返回true
7. 其实两个方法底层实现是调用了同一个方法，只不过传入的参数ClearInterrupted（是否清除中断状态），一个传的是true，一个传的是false
多读源码注释，看不懂的英语，借助翻译软件即可~