ES中提供了 FROM/SIZE 分页，但这种分页有性能瓶颈。

Scroll会以间隔时间滚屏的方式返回全部的查询数据，可以作为数据量很大的情况下，分页的一个替代方案

完整的示例如下：

public void scroll(){        RestHighLevelClient client = elasticClient.getRestHighLevelClient();        //初始化scroll        final Scroll scroll = new Scroll(TimeValue.timeValueMinutes(1L)); //设定滚动时间间隔        SearchRequest searchRequest = new SearchRequest();        searchRequest.scroll(scroll);        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();        searchSourceBuilder.query(matchAllQuery());        searchSourceBuilder.size(5); //设定每次返回多少条数据        searchRequest.source(searchSourceBuilder);        SearchResponse searchResponse = null;        try {            searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);        } catch (IOException e) {            e.printStackTrace();        }        String scrollId = searchResponse.getScrollId();        SearchHit[] searchHits = searchResponse.getHits().getHits();        System.out.println("-----首页-----");        for (SearchHit searchHit : searchHits) {            System.out.println(searchHit.getSourceAsString());        }        //遍历搜索命中的数据，直到没有数据        while (searchHits != null && searchHits.length > 0) {            SearchScrollRequest scrollRequest = new SearchScrollRequest(scrollId);            scrollRequest.scroll(scroll);            try {                searchResponse = client.scroll(scrollRequest, RequestOptions.DEFAULT);            } catch (IOException e) {                e.printStackTrace();            }            scrollId = searchResponse.getScrollId();            searchHits = searchResponse.getHits().getHits();            if (searchHits != null && searchHits.length > 0) {                System.out.println("-----下一页-----");                for (SearchHit searchHit : searchHits) {                    System.out.println(searchHit.getSourceAsString());                }            }        }        //清除滚屏        ClearScrollRequest clearScrollRequest = new ClearScrollRequest();        clearScrollRequest.addScrollId(scrollId);//也可以选择setScrollIds()将多个scrollId一起使用        ClearScrollResponse clearScrollResponse = null;        try {            clearScrollResponse = client.clearScroll(clearScrollRequest,RequestOptions.DEFAULT);        } catch (IOException e) {            e.printStackTrace();        }        boolean succeeded = clearScrollResponse.isSucceeded();        System.out.println("succeeded:" + succeeded);    }