ElasticSearch High Level REST API【3】Scroll 滚屏

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);
    }