@Override
    public void pushWhenNoDuplicate(Request request, Task task) {
        if (request.getPriority() == 0) {
            noPriorityQueue.add(request);
        } else if (request.getPriority() > 0) {
            priorityQueuePlus.put(request);
        } else {
            priorityQueueMinus.put(request);
        }
    }
Priority scheduler. Request with higher priority will poll earlier. <br>

@author code4crafter@gmail.com <br>
@since 0.2.1
webmagic-core/src/main/java/us/codecraft/webmagic/scheduler/PriorityScheduler.java