Java项目中基于Hibernate分页总结

1,First of all,  we should have a wrapper class for page,this class can calculate the startRow by the number of result,pageSize,and currentPage.

public class Pager extends BaseBO {
    private static final int DEFAULT_PAGE_SIZE = 10;
    private int totalRows;
    private int pageSize = 10;
    private int currentPage;
    private int totalPages;
    private int startRow;
     public Pager(int _totalRows, int _pageSize, int _currentPage) {
        init(_totalRows, _pageSize, _currentPage);
    }
     private void init(int _totalRows, int _pageSize, int _currentPage) {
        totalRows = _totalRows;
        pageSize = _pageSize;
        currentPage = _currentPage;

        if (totalRows < 0) {
            totalRows = 0;
        }

        if (pageSize < 1) {
            pageSize = DEFAULT_PAGE_SIZE;
        }
        totalPages = totalRows / pageSize;
        int mod = totalRows % pageSize;
        if (mod > 0) {
            totalPages++;
        }
        if (currentPage > totalPages) {
            currentPage = totalPages;
        }
        if (currentPage < 1) {
            currentPage = 1;
        }
        startRow = (currentPage - 1) * pageSize;
    }
}

then ,we should have a wrapper class for pageList:

public class PageList extends BaseBO {

    /** 分页信息 */
    private Pager pager;

    /** 页记录列表 */
    private List list;
   ................//omit the method of get and set
}

2，In  the DAO，we can see ：

public class YfsjIssueDAOImpl extends BaseHibernateDaoImpl｛
    public PageList findLogicB1(YfsjIssueModel condition){
          ..............//service code omitted
        return findPageListWithHql(countHql, qryHql,pageSize,currentPage);
    ｝
｝

from this code,we find that all the DAO  extend  from the Class of BaseHibernateDaoImpl .And the Class of BaseHibernateDaoImpl declare a method called findPageListWithHql  to control paging.
3,then let's learn this paging method declared in BaseHibernateDaoImpl :

abstract public class BaseHibernateDaoImpl extends HibernateDaoSupport implements BaseHibernateDao { /**
     * find the paging result
     *
     * @param countHql
     *            find the number of result by  HQL
     * @param qryHql
     *            find the  result by   HQL
     * @param pageSize
     *            the number of result  by each page
     * @param currentPage
     *            the page number
     * @return
     */
    protected PageList findPageListWithHql(String countHql, String qryHql, int pageSize, int currentPage) {
        return findPageListWithHql(countHql, qryHql, null, pageSize, currentPage);
    }
　　 protected PageList findPageListWithHql(String countHql, String qryHql, List paramList, int pageSize, int currentPage) {
         PageList list = null;
　　       int totalRows = getCount(countHql, paramList);           //get the number of result

          if (totalRows < 1) {
            return list;
         }
　　     
         list = new PageList();
         Pager pager = new Pager(totalRows, pageSize, currentPage);  //create a new instance of the page model
         list.setPager(pager);
         list.setList(this.findPageList(qryHql, paramList, pager.getStartRow(), pager.getPageSize()));
        return list;
    }

then,let's learn the method called getCount()  to get the number of result,  this method is very easy.

 protected int getCount(String hql, List paramList) {
        try {
            Query query = this.getSession().createQuery(hql);

            if (paramList != null && paramList.size() > 0) {
                for (int i = 0; i < paramList.size(); i++) {
                    query.setParameter(i, paramList.get(i));
                }
            }

            List list = query.list();
            return ((Integer) list.get(0)).intValue();
        } catch (HibernateException ex) {
            throw new RuntimeException(ex);
        }
    }
    

then ,let's see the last method  called findPageList that to  find the result :

 protected List findPageList(String hql, List paramList, int startRow, int pageSize) {
        try {
            Query query = this.getSession().createQuery(hql);

            if (paramList != null && paramList.size() > 0) {
                for (int i = 0; i < paramList.size(); i++) {
                    query.setParameter(i, paramList.get(i));
                }
            }

            query.setFirstResult(startRow);
            query.setMaxResults(pageSize);
            return query.list();
        } catch (HibernateException ex) {
            throw new RuntimeException(ex);
        }
    }