@Override
                        public int compare(Map.Entry<String, MultiPageModel> o1, Map.Entry<String, MultiPageModel> o2) {
                            try {
                                int i1 = Integer.parseInt(o1.getKey());
                                int i2 = Integer.parseInt(o2.getKey());
                                return i1 - i2;
                            } catch (NumberFormatException e) {
                                return o1.getKey().compareTo(o2.getKey());
                            }
                        }
A pipeline combines the result in more than one page together.<br>
Used for news and articles containing more than one web page. <br>
MultiPagePipeline will store parts of object and output them when all parts are extracted.<br>

@author code4crafter@gmail.com <br>
@since 0.2.0
webmagic-extension/src/main/java/us/codecraft/webmagic/pipeline/MultiPagePipeline.java