分頁設計與實現

一、首先寫出DAO層的獲取分頁數據方法

@SuppressWarnings("unchecked") @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED) public <T> QueryResult<T> getScrollData(Class<T> entityClass, int firstindex,int maxresult,String wherejpql,Object[] queryParams,LinkedHashMap<String,String> order) { QueryResult<T> qr=new QueryResult<T>(); String entityName=getEntityName(entityClass); Query query=em.createQuery("select o from "+entityName+" o "+(wherejpql==null ? "" :"where "+wherejpql)+buildOrderby(order)); setQueryParams(query, queryParams); if(firstindex!=-1 && maxresult!=-1){ query.setFirstResult(firstindex); query.setMaxResults(maxresult); } qr.setResultlist(query.getResultList()); query=em.createQuery("select count(o) from "+entityName+" o "+(wherejpql==null ? "" :"where "+wherejpql)); setQueryParams(query, queryParams); qr.setTotalrecord((Long)query.getSingleResult()); return qr; } @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED) public <T> QueryResult<T> getScrollData(Class<T> entityClass, int firstindex, int maxresult, LinkedHashMap<String, String> order) { return getScrollData(entityClass, firstindex, maxresult,null, null, order); } @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED) public <T> QueryResult<T> getScrollData(Class<T> entityClass, int firstindex, int maxresult, String wherejpql, Object[] queryParams) { return getScrollData(entityClass, firstindex, maxresult,wherejpql, queryParams, null); } @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED) public <T> QueryResult<T> getScrollData(Class<T> entityClass, int firstindex, int maxresult) { return getScrollData(entityClass, firstindex, maxresult,null, null, null); } @Transactional(readOnly=true,propagation=Propagation.NOT_SUPPORTED) public <T> QueryResult<T> getScrollData(Class<T> entityClass) { return getScrollData(entityClass,-1, -1); } /** * 組裝order by 語句 * @param order * @return example:order by o.key1 desc,o.key2 asc */ protected String buildOrderby(LinkedHashMap<String,String> order){ StringBuffer orderby=new StringBuffer(""); if(order!=null && order.size()>0){ orderby.append(" order by "); for(String key:order.keySet()){ orderby.append("o.").append(key).append(" ").append(order.get(key)).append(","); } orderby.deleteCharAt(orderby.length()-1); } return orderby.toString(); } /** * * @param query * @param queryParams */ protected void setQueryParams(Query query,Object[] queryParams){ if(queryParams!=null && queryParams.length>0){ for(int i=0;i<queryParams.length;i++){ query.setParameter(i+1,queryParams[i]); } } } /** * 獲取實體名稱 * @param <T> * @param entityClass 實體類 * @return */ protected <T> String getEntityName(Class<T> entityClass){ String entityName=entityClass.getSimpleName(); Entity entity=entityClass.getAnnotation(Entity.class); if(entity.name()!=null && entity.name().length()>0){ entityName=entity.name(); } return entityName; } }

二、寫控制層Action

public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { BuyerForm formbean=(BuyerForm)form; LinkedHashMap<String,String> order=new LinkedHashMap<String, String>(); order.put("regTime", "desc"); /** * 定義一個PageView對象，傳入每頁記錄數12，和當前第幾頁 * 得到開始記錄索引 */ PageView<Brand> pv=new PageView<Brand>(12,formbean.getPage()); /** * 調用業務層的查詢語句得到記錄。 */ QueryResult<Buyer> qr=buyerService.getScrollData(Buyer.class,pv.getFirstResult(), pv.getMaxresult(),order); /** * 調用PageView中一set方法,得到總記錄數和總記錄。 * 至此完成了頁面所需的一切數據的需要。 */ pv.setQueryResult(qr); request.setAttribute("pageView", pv); return mapping.findForward("list"); }

三、由此Action知道必須要定義一個類：PageView，此類用來封閉查詢到的分頁相關數據的信息。

      下面來看一下這個類的設計：

package cn.yang.bean; import java.util.List; import cn.yang.bean.product.ProductType; public class PageView<T>{ /*分頁數據*/ private List<T> records; /*頁碼開始索引和結束索引*/ private PageIndex pageIndex; /*總頁數*/ private long totalpage=1; /*每頁顯示的記錄數*/ private int maxresult=12; /*當前頁*/ private int currentpage=1; /*總記錄數*/ private long totalrecord; /*開始查詢第幾個記錄*/ private int firstResult; public int getFirstResult() { return firstResult; } public PageView(int maxresult, int currentpage) { this.maxresult = maxresult; this.currentpage = currentpage; this.firstResult=(currentpage-1)*maxresult; } public long getTotalrecord() { return totalrecord; } public void setQueryResult(QueryResult queryResult){ setTotalrecord(queryResult.getTotalrecord()); setRecords(queryResult.getResultlist()); } public void setTotalrecord(long totalrecord) { this.totalrecord = totalrecord; //System.out.println("*********"+this.totalrecord); } public List<T> getRecords() { return records; } public void setRecords(List<T> list) { this.records = list; this.totalpage=totalrecord%maxresult==0?totalrecord/maxresult:totalrecord/maxresult+1; if(totalpage==0) totalpage=1; this.pageIndex=WebTool.getPageIndex(maxresult, currentpage, totalpage); } public PageIndex getPageIndex() { return pageIndex; } public long getTotalpage() { return totalpage; } public int getMaxresult() { return maxresult; } public int getCurrentpage() { return currentpage; } }

通過此類就能獲得分頁頁面所需的所有數據；包括總頁碼、起始頁、結束頁、List集合的數據。

其中還有一個類WebTool，此類用以獲取起始頁與結束頁的頁碼，其代碼如下所示：

public class WebTool { public static PageIndex getPageIndex(int maxresult,int currentpage,long totalpage){ long startindex=0; long endindex=0; if(currentpage+maxresult/2<totalpage){ if(currentpage>maxresult/2){ startindex=maxresult%2==0 ? currentpage-maxresult/2+1 : currentpage-maxresult/2; endindex=currentpage+maxresult/2; }else{ startindex=1; endindex=maxresult<totalpage ? maxresult : totalpage; } }else{ startindex=totalpage-maxresult<0 ? 1 : totalpage-maxresult+1; endindex=totalpage; } return new PageIndex(startindex,endindex); } /* public static PageIndex getPageIndex(long viewPageCount,int currentPage,long totalpage){ long startindex=currentPage-(viewPageCount%2==0 ? viewPageCount/2-1 :viewPageCount/2); long endindex=currentPage+viewPageCount/2; if(startindex<1){ startindex=1; endindex=totalpage>viewPageCount ? viewPageCount :totalpage; } if(endindex>totalpage){ endindex=totalpage; startindex=totalpage-viewPageCount<0 ? 1 :totalpage-viewPageCount+1; } return new PageIndex(startindex,endindex); }*/ }

至此分頁所需數據已全部獲得，剩下的任務就是前端頁面的設計，在此不做介紹。