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);
}