为什么我一天会收到几次CancelledKeyException？我应该做些什么吗？我的代码有错吗？Iteratorkeys=selector.selectedKeys().iterator();while(keys.hasNext()){SelectionKeykey=(SelectionKey)keys.next();keys.remove();try{if(key.isValid()){if(key.isReadable()){readHandler.handle((Connection)key.attachment());}if(key.isWritable()){writeH