protected void sleep(int time) {
        try {
            Thread.sleep(time);
        } catch (InterruptedException e) {
            logger.error("Thread interrupted when sleep",e);
            Thread.currentThread().interrupt();
        }
    }
Process specific urls without url discovering.

@param urls urls to process
webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java