ssh整合开发中的分页方案（转）
? 分页显示一直是web开发中一大烦琐的难题，传统的网页设计只在一个JSP或者ASP页面中书写所有关于数据库操作的代码，那样做分页可能简单一点，但当把网站分层开发后，分页就比较困难了，下面是我做Spring+Hibernate+Struts2项目时设计的分页代码，与大家分享交流。
1、DAO层接口的设计，在MemberDao接口中定义了如下两个方法：
public?interface?MemberDao{
????????//省略了其他的代码????
????/**?????*?分页查询?????*?@param?hql?查询的条件?????*?@param?offset?开始记录?????*?@param?length?一次查询几条记录?????*?@return
?????*/????public?List?queryForPage(final?String?hql,final?int?offset,final?int?length);????????/**?????*?查询所有记录数?????*?@param?hql?查询的条件?????*?@return?总记录数?????*/????public?int?getAllRowCount(String?hql);
}?
2、DAO层实现类MemberDaoImpl对上面两个方法的实现如下：
public?class?MemberDaoImpl?extends?HibernateDaoSupport?implements?MemberDao?{???????//省略了其他的代码????????/**?????*?分页查询?????*?@param?hql?查询的条件?????*?@param?offset?开始记录?????*?@param?length?一次查询几条记录?????*?@return?????*/????public?List?queryForPage(final?String?hql,final?int?offset,final?int?length){????????List?list?=?getHibernateTemplate().executeFind(new?HibernateCallback(){????????????public?Object?doInHibernate(Session?session)?throws?HibernateException,SQLException{????????????????Query?query?=?session.createQuery(hql);????????????????query.setFirstResult(offset);????????????????query.setMaxResults(length);????????????????List?list?=?query.list();????????????????return?list;????????????}????????});????????return?list;????}????????????/**?????*?查询所有记录数?????*?@return?总记录数?????*/????public?int?getAllRowCount(String?hql){????????return?getHibernateTemplate().find(hql).size();????}}??????? 细心的读者会发现，这个类继承了HibernateDaoSupport类，HibernateDaoSupport是Spring提供的对Hibernate支持的类，getHibernateTemplate().executeFind(new HibernateCallback(){....})方法中的参数，我们使用了接口回调，在其参数内，我们能像原生的Hibernate一样调用query.setFirstResult(offset)和query.setMaxResults(length)来实现分页查询功能。
3、下面我们来新建一个保存分页信息的类PageBean,具体代码如下：
public?class?PageBean?{????????private?List?list;????????//要返回的某一页的记录列表????????private?int?allRow;?????????//总记录数????private?int?totalPage;????????//总页数????private?int?currentPage;????//当前页????private?int?pageSize;????????//每页记录数????????private?boolean?isFirstPage;????//是否为第一页????private?boolean?isLastPage;????????//是否为最后一页????private?boolean?hasPreviousPage;????//是否有前一页????private?boolean?hasNextPage;????????//是否有下一页????????????public?List?getList()?{????????return?list;????}????public?void?setList(List?list)?{????????this.list?=?list;????}????public?int?getAllRow()?{????????return?allRow;????}????public?void?setAllRow(int?allRow)?{????????this.allRow?=?allRow;????}????public?int?getTotalPage()?{????????return?totalPage;????}????public?void?setTotalPage(int?totalPage)?{????????this.totalPage?=?totalPage;????}????public?int?getCurrentPage()?{????????return?currentPage;????}????public?void?setCurrentPage(int?currentPage)?{????????this.currentPage?=?currentPage;????}????public?int?getPageSize()?{????????return?pageSize;????}????public?void?setPageSize(int?pageSize)?{????????this.pageSize?=?pageSize;????}????????/**?????*?初始化分页信息?????*/????public?void?init(){????????this.isFirstPage?=?isFirstPage();????????this.isLastPage?=?isLastPage();????????this.hasPreviousPage?=?isHasPreviousPage();????????this.hasNextPage?=?isHasNextPage();????}????????/**?????*?以下判断页的信息,只需getter方法(is方法)即可?????*?@return?????*/????????public?boolean?isFirstPage()?{????????return?currentPage?==?1;????//?如是当前页是第1页????}????public?boolean?isLastPage()?{????????return?currentPage?==?totalPage;????//如果当前页是最后一页????}????public?boolean?isHasPreviousPage()?{????????return?currentPage?!=?1;????????//只要当前页不是第1页????}????public?boolean?isHasNextPage()?{????????return?currentPage?!=?totalPage;????//只要当前页不是最后1页????}????????????/**?????*?计算总页数,静态方法,供外部直接通过类名调用?????*?@param?pageSize?每页记录数?????*?@param?allRow?总记录数?????*?@return?总页数?????*/????public?static?int?countTotalPage(final?int?pageSize,final?int?allRow){????????int?totalPage?=?allRow?%?pageSize?==?0???allRow/pageSize?:?allRow/pageSize+1;????????return?totalPage;????}????????/**?????*?计算当前页开始记录?????*?@param?pageSize?每页记录数?????*?@param?currentPage?当前第几页?????*?@return?当前页开始记录号?????*/????public?static?int?countOffset(final?int?pageSize,final?int?currentPage){????????final?int?offset?=?pageSize*(currentPage-1);????????return?offset;????}????????/**?????*?计算当前页,若为0或者请求的URL中没有"?page=",则用1代替?????*?@param?page?传入的参数(可能为空,即0,则返回1)?????*?@return?当前页?????*/????public?static?int?countCurrentPage(int?page){????????final?int?curPage?=?(page==0?1:page);????????return?curPage;????}}
4、Service层接口的设计：
public?interface?MemberService?{????//省略其他的代码????/**?????*?分页查询?????*?@param?currentPage?当前第几页?????*?@param?pageSize?每页大小?????*?@return?封闭了分页信息(包括记录集list)的Bean?????*/????public?PageBean?queryForPage(int?pageSize,int?currentPage);}
5、Service层实现类的部分内码如下：
public?class?MemberServiceImpl?implements?MemberService?{????//通过applicationContext.xml配置文件注入MemberDao的值????private?MemberDao?memberDao;????public?void?setMemberDao(MemberDao?memberDao)?{????????this.memberDao?=?memberDao;????}????????/**?????*?分页查询?????*?@param?currentPage?当前第几页?????*?@param?pageSize?每页大小?????*?@return?封闭了分页信息(包括记录集list)的Bean?????*/????public?PageBean?queryForPage(int?pageSize,int?page){????????final?String?hql?=?"from?Member";????????//查询语句????????int?allRow?=?memberDao.getAllRowCount(hql);????//总记录数????????int?totalPage?=?PageBean.countTotalPage(pageSize,?allRow);????//总页数????????final?int?offset?=?PageBean.countOffset(pageSize,?page);????//当前页开始记录????????final?int?length?=?pageSize;????//每页记录数????????final?int?currentPage?=?PageBean.countCurrentPage(page);????????List<Member>?list?=?memberDao.queryForPage(hql,offset,?length);????????//"一页"的记录????????????????//把分页信息保存到Bean中????????PageBean?pageBean?=?new?PageBean();????????pageBean.setPageSize(pageSize);????????????pageBean.setCurrentPage(currentPage);????????pageBean.setAllRow(allRow);????????pageBean.setTotalPage(totalPage);????????pageBean.setList(list);????????pageBean.init();????????return?pageBean;????}
6、在Struts2中调用queryForPageMemberService层的queryForPage（）方法即可return一个包含分页信息、符合条件的结果集list， 代码如下：
public?class?ListMember?extends?ActionSupport{????//通过applicationContext.xml配置文件注入memberService的值????private?MemberService?memberService;????public?void?setMemberService(MemberService?memberService)?{????????this.memberService?=?memberService;????}????????private?int?page;????//第几页????????private?PageBean?pageBean;????//包含分布信息的bean????????public?int?getPage()?{????????return?page;????}????public?void?setPage(int?page)?{????????//若URL中无此参数,会默认为第1页????????this.page?=?page;????}????public?PageBean?getPageBean()?{????????return?pageBean;????}????public?void?setPageBean(PageBean?pageBean)?{????????this.pageBean?=?pageBean;????}????@Override????public?String?execute()?throws?Exception?{????????//分页的pageBean,参数pageSize表示每页显示记录数,page为当前页????????this.pageBean?=?memberService.queryForPage(2,?page);????????return?SUCCESS;????}}
7、最后在listMember.jsp页面中，用到了Struts2标签：
<s:iterator?value="pageBean.list">????????????<s:property?value="title"/>????????????<a?href="getArticle.action?id=<s:property?value="id"/>">modify</a>????????????<a?href="deleteArticle.action?id=<s:property?value="id"/>"?onclick="return?askDel()"/>delete</a><br/>????????</s:iterator>????????共<s:property?value="pageBean.allRow"/>?条记录????????共<s:property?value="pageBean.totalPage"/>?页????????当前第<s:property?value="pageBean.currentPage"/>页<br/>????????????????<s:if?test="%{pageBean.currentPage?==?1}">????????????第一页?上一页????????</s:if>????????<s:else>????????????<a?href="listMyArticle.action?page=1">第一页</a>????????????<a?href="listMyArticle.action?page=<s:property?value="%{pageBean.currentPage-1}"/>">上一页</a>????????</s:else>????????<s:if?test="%{pageBean.currentPage?!=?pageBean.totalPage}">????????????<a?href="listMyArticle.action?page=<s:property?value="%{pageBean.currentPage+1}"/>">下一页</a>????????????<a?href="listMyArticle.action?page=<s:property?value="pageBean.totalPage"/>">最后一页</a>????????</s:if>????????<s:else>????????????下一页?最后一页????????</s:else>?到这里，Hibernate+Spring+Struts2整合开发中的分页问题就已经解决了，在我上述过程中，省略了许多Hibernate,Spring,Struts2的配置，那不是本文的重点，大家可以参考有关的书与资料，由于篇幅有限，在此就不一一列举。在以后的文章中，我也会详细地跟大家讲述SSH整合开发。
