我已经知道怎么做了事件调度线程 http://docs.oracle.com/javase/tutorial/uiswing/concurrency/index.html作品。如果事件调度线程中存在如下所示的短事件和长事件，则应用程序无法响应。
为了提高 Swing 的响应能力，事件调度线程应该只用于短事件。而长事件应该在 SwingWorkers 上执行。
想象一下有很多短事件。
The events should be executed in Event Dispatch thread and you have a special event which you want to be executed before other events existing in Event Dispatch Thread queue. But, events will be enqueued to the end of the queue by default and even InvokeLater do the same.
那么，有什么解决方案可以将事件排队到事件调度线程的开头吗？
虽然更换了EventQueue是一种正确的方法，由于内置，所以并不是真正必要的EventQueue已经支持优先级了。唯一的问题是它只支持内部 API 使用，所以我们只需要了解它是如何工作的；
//from EventQueue.java...
private static final int LOW_PRIORITY = 0;
private static final int NORM_PRIORITY = 1;
private static final int HIGH_PRIORITY = 2;
private static final int ULTIMATE_PRIORITY = 3;
private static final int NUM_PRIORITIES = ULTIMATE_PRIORITY + 1;
/*
* We maintain one Queue for each priority that the EventQueue supports.
* That is, the EventQueue object is actually implemented as
* NUM_PRIORITIES queues and all Events on a particular internal Queue
* have identical priority. Events are pulled off the EventQueue starting
* with the Queue of highest priority. We progress in decreasing order
* across all Queues.
*/
private Queue[] queues = new Queue[NUM_PRIORITIES];
//...skipped some parts...
/**
* Causes <code>runnable</code> to have its <code>run</code>
* method called in the {@link #isDispatchThread dispatch thread} of
* {@link Toolkit#getSystemEventQueue the system EventQueue}.
* This will happen after all pending events are processed.
*
* @param runnable the <code>Runnable</code> whose <code>run</code>
* method should be executed
* asynchronously in the
* {@link #isDispatchThread event dispatch thread}
* of {@link Toolkit#getSystemEventQueue the system EventQueue}
* @see #invokeAndWait
* @see Toolkit#getSystemEventQueue
* @see #isDispatchThread
* @since 1.2
*/
public static void invokeLater(Runnable runnable) {
Toolkit.getEventQueue().postEvent(
new InvocationEvent(Toolkit.getDefaultToolkit(), runnable));
}
/**
* Posts a 1.1-style event to the <code>EventQueue</code>.
* If there is an existing event on the queue with the same ID
* and event source, the source <code>Component</code>'s
* <code>coalesceEvents</code> method will be called.
*
* @param theEvent an instance of <code>java.awt.AWTEvent</code>,
* or a subclass of it
* @throws NullPointerException if <code>theEvent</code> is <code>null</code>
*/
public void postEvent(AWTEvent theEvent) {
SunToolkit.flushPendingEvents(appContext);
postEventPrivate(theEvent);
}
/**
* Posts a 1.1-style event to the <code>EventQueue</code>.
* If there is an existing event on the queue with the same ID
* and event source, the source <code>Component</code>'s
* <code>coalesceEvents</code> method will be called.
*
* @param theEvent an instance of <code>java.awt.AWTEvent</code>,
* or a subclass of it
*/
private final void postEventPrivate(AWTEvent theEvent) {
theEvent.isPosted = true;
pushPopLock.lock();
try {
if (nextQueue != null) {
// Forward the event to the top of EventQueue stack
nextQueue.postEventPrivate(theEvent);
return;
}
if (dispatchThread == null) {
if (theEvent.getSource() == AWTAutoShutdown.getInstance()) {
return;
} else {
initDispatchThread();
}
}
postEvent(theEvent, getPriority(theEvent));
} finally {
pushPopLock.unlock();
}
}
private static int getPriority(AWTEvent theEvent) {
if (theEvent instanceof PeerEvent) {
PeerEvent peerEvent = (PeerEvent)theEvent;
if ((peerEvent.getFlags() & PeerEvent.ULTIMATE_PRIORITY_EVENT) != 0) {
return ULTIMATE_PRIORITY;
}
if ((peerEvent.getFlags() & PeerEvent.PRIORITY_EVENT) != 0) {
return HIGH_PRIORITY;
}
if ((peerEvent.getFlags() & PeerEvent.LOW_PRIORITY_EVENT) != 0) {
return LOW_PRIORITY;
}
}
int id = theEvent.getID();
if ((id >= PaintEvent.PAINT_FIRST) && (id <= PaintEvent.PAINT_LAST)) {
return LOW_PRIORITY;
}
return NORM_PRIORITY;
}
/**
* Posts the event to the internal Queue of specified priority,
* coalescing as appropriate.
*
* @param theEvent an instance of <code>java.awt.AWTEvent</code>,
* or a subclass of it
* @param priority the desired priority of the event
*/
private void postEvent(AWTEvent theEvent, int priority) {
if (coalesceEvent(theEvent, priority)) {
return;
}
EventQueueItem newItem = new EventQueueItem(theEvent);
cacheEQItem(newItem);
boolean notifyID = (theEvent.getID() == this.waitForID);
if (queues[priority].head == null) {
boolean shouldNotify = noEvents();
queues[priority].head = queues[priority].tail = newItem;
if (shouldNotify) {
if (theEvent.getSource() != AWTAutoShutdown.getInstance()) {
AWTAutoShutdown.getInstance().notifyThreadBusy(dispatchThread);
}
pushPopCond.signalAll();
} else if (notifyID) {
pushPopCond.signalAll();
}
} else {
// The event was not coalesced or has non-Component source.
// Insert it at the end of the appropriate Queue.
queues[priority].tail.next = newItem;
queues[priority].tail = newItem;
if (notifyID) {
pushPopCond.signalAll();
}
}
}
如你看到的EventQueue有 4 个不同的队列LOW, NORM, HIGH and ULTIMATE, SwingUtilities.invokeLater(Runnable) or EventQueue.invokeLater(Runnable)包裹你的Runnable进入一个InvocationEvent并打电话postEvent(AWTEvent)方法。此方法在线程和调用之间进行一些同步postEvent(AWTEvent, int)像这样postEvent(theEvent, getPriority(theEvent));现在有趣的部分是如何getPriority(AWTEvent)有效，基本上它给除了某些事件之外的每个事件提供正常的优先级PaintEvents and PeerEvents.
所以你需要做的就是包裹你的Runnable into a PeerEvent with ULTIMATE_PRIORTY代替InvocationEvent像这样;
Toolkit.getDefaultToolkit().getSystemEventQueue()
.postEvent(new PeerEvent(Toolkit.getDefaultToolkit(), () -> {
//execute your high priority task here!
System.out.println("I'm ultimate prioritized in EventQueue!");
}, PeerEvent.ULTIMATE_PRIORITY_EVENT));
您可以查看完整的源代码事件队列 http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b27/java/awt/EventQueue.java and 同行事件 http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b27/sun/awt/PeerEvent.java .