在大数量查询处理时，为了避免出现OOM，可以采用cursor查询

1、dao层

import org.apache.ibatis.cursor.Cursor; //导包

//接口
Cursor<ROIReport> queryROIReportsCursor(ROIReportQuery params);

<select id="queryROIReportsCursor" resultType="com.xxx.ROIReport">
xxxxxxxxx对应自己的查询语句
</select>

service层

//service接口
Cursor<ROIReport> queryROIReportsCursor(ROIReportQuery params);

//serviceImpl
@Override
public Cursor<ROIReport> queryROIReportsCursor(ROIReportQuery params) {
	return salesMarketsMapper.queryROIReportsCursor(params);
}

controller层

//记得加上事务，不然游标在查询完就会关闭，报错
@ResponseBody
	@PostMapping("roiReportExport")
	@Transactional(readOnly = true)
	public void roiReportCursor(@RequestBody @Valid ROIReportParams params) throws ParseException {
		ROIReportQuery roiReportQuery = roiReportParams.toROIReportQuery();

		try (Cursor<ROIReport> roiReports = salesMarketsReportService.queryROIReportsCursor(roiReportQuery)) {
			Iterator<ROIReport> iterator = roiReports.iterator();
			while (iterator.hasNext()) {
				ROIReport next = iterator.next();
				System.out.println(next.getMarketName());
				System.out.println(next.getId());
				//xxxx自己业务逻辑
			}
		} catch (Exception e) {
			System.out.println(e);
		}
	}

使用cursor一定要加上事务，不然会报错：java.lang.IllegalStateException: A Cursor is already closed.