Paginate the list collection and display the data on the page

Tools

Tool class code:

public class PageUtil {/*** start paging* @param list* @param pageNum page number* @param pageSize how many pieces of data per page* @return*/public static List startPage(List list, Integer pageNum,Integer pageSize) {if (list == null) {return null;}if (list.size() == 0) {return null;}Integer count = list.size(); // total number of recordsInteger pageCount = 0; // page countif (count % pageSize == 0) {pageCount = count / pageSize;} else {pageCount = count / pageSize + 1;}int fromIndex = 0; // start indexint toIndex = 0; // end indexif (pageNum > pageCount){return null;}if (pageNum != pageCount) {System.out.println("pageNum====>"+pageNum);fromIndex = (pageNum - 1) * pageSize;System.out.println("fromindex===>"+fromIndex);toIndex = fromIndex + pageSize;} else {System.out.println("from====>"+fromIndex);fromIndex = (pageNum - 1) * pageSize;toIndex = count;}List pageList = list.subList(fromIndex, toIndex);return pageList;}}

Usage in the project

Data set found from the database: noGroupList noGroup = studentsService.queryStudentNotInGroup(campusId, phone);Call the method of the tool class:List page = PageUtil.startPage(noGroup,pageNum,pageSize);Total number:Integer count = noGroup.size();Total page number:Integer totalPage = count % 10 == 0 ? count / 10 : count / 10 + 1;map.put("totalPage", totalPage);map.put("page", page);

It has been tested and works, I hope it can help you

**Modify it: if there is too much data, if (pageNum != pageCount) this line will be judged wrong, and the test will be!= Modified to!equals---------> if (!pageNum.equals(pageCount)) **

Modification: If the incoming page number is greater than the total page number, a null pointer exception will be reported, so add a judgment:
if (pageNum > pageCount){
return null;
}

Note: This paging tool class is only suitable for a small amount of data. For millions of data, the response time is very long.If there are millions of data, the query takes time, so the response is very slow, and a better method is still under consideration. If you have a better method, please provide it.