回想当年刚开始做Java开发的时候，如何停止线程运行可是难倒了一批人，停止线程的方法众说纷纭：
1. 调用Thread.stop() :
Thread thread = new Thread(){
@Override
public void run() {
for (int i=0; i < 999 && !isCanceled; i++) {
System.out.println("哈哈，我还没死...");
}
}
};
thread.start();
// kill you now
thread.stop();
点评: 不用多说，直接拉出去斩了
2. 线程外面定义boolean变量标识为是否已经取消，线程里每个循环地方加判断，变量变成了取消则停止循环:
private volatile boolean isCanceled = false;
new Thread(){
@Override
public void run() {
for (int i=0; i < 999 && !isCanceled; i++) {
System.out.println("哈哈，我还没死...");
}
}
}.start();
// kill thread
isCanceled = true;
点评： 太片面，线程里Thread.sleep(999999)取消不了的
3. 通过调用interrupt() ：
Thread thread = new Thread(){
@Override
public void run() {
sleep(99999);
System.out.println("刚睡醒，我还没死！！！");
}
};
thread.start();
// kill you now
thread.interrupt();
点评：也是太片面，for循环取消不了
4. 以上方案意思是有那么一点了，只是零零碎碎，如何将两个方案结合是今天的第一个话题。
在Thread内提供了一个方法叫interrupted()， 其返回值即告知是否线程被interrupt()执行过，简单说：无需自己定义boolean变量，可以用它代替，如果线程能被interrupt()而停止正好，如果是内部循环操作可以用它作为循环停止的条件：
Thread thread = new Thread(){
@Override
public void run() {
for (int i=0; i < 999 && !Thread.interrupted(); i++) {
System.out.println("哈哈，我还没死...");
}
}
};
其实，还有一种情况是停止不了的，类似socket/http通信这种不能被interrputted的情况，当然也有巧妙的办法：重载Thread的interrput()方法：
// 重载interrupt 通过关闭socket起到关闭线程的作用
@Override
public void interrupt() {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
今天的第二个话题是，使用单个线程的情况在项目中极少，很多情况使用线程池托管的，那么线程池里如何停止某个task呢？
JDK5提供了ExecuteService，并通过Executors提供了多个候选的线程池选择方案，ExecutorService提交task有两种方式：execute()和submit(), 我们这里对submit()比较感兴趣，因为其中submit()会返回Feature，不管submit的是 Runnable还是Callable都会有Feature返回：
public interface ExecutorService extends Executor {
/**
* Submits a value-returning task for execution and returns a
* Future representing the pending results of the task. The
* Future's {@code get} method will return the task's result upon
* successful completion.
*
* <p>
* If you would like to immediately block waiting
* for a task, you can use constructions of the form
* {@code result = exec.submit(aCallable).get();}
*
* <p>Note: The {@link Executors} class includes a set of methods
* that can convert some other common closure-like objects,
* for example, {@link java.security.PrivilegedAction} to
* {@link Callable} form so they can be submitted.
*
* @param task the task to submit
* @param <T> the type of the task's result
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
<T> Future<T> submit(Callable<T> task);
/**
* Submits a Runnable task for execution and returns a Future
* representing that task. The Future's {@code get} method will
* return {@code null} upon <em>successful</em> completion.
*
* @param task the task to submit
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
Future<?> submit(Runnable task);
/**
* Submits a Runnable task for execution and returns a Future
* representing that task. The Future's {@code get} method will
* return the given result upon successful completion.
*
* @param task the task to submit
* @param result the result to return
* @param <T> the type of the result
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
<T> Future<T> submit(Runnable task, T result);
}
Feature对象提供了一系列API，如：
- cancel(boolean mayInterruptIfRunning) ；
- isCanceled()；
- get()；
- get(long timeout, TimeUnit unit)；
- isDone()
看到第一个API，很是让人兴奋，难倒这真的可以一步到位？但很不好意思，依然不行，其实跟第一个话题的原理一摸一样，如果内部有阻塞线程的操作会因此而退出，如： wait(), join(), sleep() 等，但是遇到IO阻塞操作，比如进行socket通信，仅仅通过调用cancel(true)是不行的，不过可以重载interrupt() 关闭socket即可, 遇到大量循环也要通过Thread.interrupted()作为循环结束的条件：
class Task extends Thread{
private Socket socket;
public Task(){
// init socket
}
// 重载interrupt 通过关闭socket起到关闭线程的作用
@Override
public void interrupt() {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void func () {
ExecutorService timer = Executors.newCachedThreadPool();
Future<?> future = timer.submit(new Task());
future.cancel(true);
}
好了，夜深了...回忆到此结束
