Servlet实现后台分页查询

相信大家在搭建后台的时候，经常会使用到分页功能，当然，目前有不少框架（如esayUI）都自带分页的实现，为了更好的理解分页原理，近期本人自己摸索了关于分页查询的一些心得。

归根结底，分页的核心还是在封装PageBean，并通过一定的算法对其进行判断，赋值

public class PageBean<T> implements Serializable{
    /**
     *
     */
    private static final long serialVersionUID = 1L;
    private int currentPage; //当前第几页 ，请求传过来
     private int pageCount;  // 每页显示多少条数据
     private int totalCount; //总记录数，查询数据获得

     private int totalPage;  //总页数， 通过  totalCount 和 pageCount计算获得

     private int startIndex; //开始索引，与pageCount 组成 limit 条件

     private List<T> pageData;

     //分页显示的页数，如 1,2,3,4
     private int start;
     private int end;

     public PageBean(int currentPage,int pageCount,int totalCount){
         this.currentPage=currentPage;
         this.pageCount=pageCount;
         this.totalCount=totalCount;

         if(totalCount % pageCount==0){
             this.totalPage = totalCount/ pageCount;
         }else{
             this.totalPage= totalCount/pageCount+1;
         }

         this.startIndex = (currentPage-1)*pageCount;

         this.start=1;
         this.end=5;

         if(pageCount<=5){
             this.end= this.totalPage;
         }else{

             this.start=currentPage-2;
             this.end = currentPage+2;

             if(start<=0){
                 this.start=1;
                 this.end=5;
             }
             if(this.end > this.totalPage){
                 this.end=totalPage;
                 this.start=end-4;
             }
         }
     }

    public int getCurrentPage() {
        return currentPage;
    }

    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }

    public int getPageCount() {
        return pageCount;
    }

    public void setPageCount(int pageCount) {
        this.pageCount = pageCount;
    }

    public int getTotalCount() {
        return totalCount;
    }

    public void setTotalCount(int totalCount) {
        this.totalCount = totalCount;
    }

    public int getTotalPage() {
        return totalPage;
    }

    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }

    public int getStartIndex() {
        return startIndex;
    }

    public void setStartIndex(int startIndex) {
        this.startIndex = startIndex;
    }

    public List<T> getPageData() {
        return pageData;
    }

    public void setPageData(List<T> pageData) {
        this.pageData = pageData;
    }

    public int getStart() {
        return start;
    }

    public void setStart(int start) {
        this.start = start;
    }

    public int getEnd() {
        return end;
    }

    public void setEnd(int end) {
        this.end = end;
    }

    public static long getSerialversionuid() {
        return serialVersionUID;
    }

}

Controller层

         int currentPage = Integer.valueOf(request.getParameter("currentPage"));

         int pageCount=7;

         BlogTypeService blogType = new BlogTypeServiceImpl();

         PageBean<BlogType> page = blogType.page(currentPage, pageCount);
         request.setAttribute("page", page);
         request.getRequestDispatcher("/jsp/blogType.jsp").forward(request, response);

service层

public PageBean<BlogType> page(int currentPage,int pageCount) {
        int totalCount=blogType.getTotal();

        PageBean<BlogType> pageBean = new PageBean<>(currentPage, pageCount, totalCount);
        int startIndex = pageBean.getStartIndex();
        pageBean.setPageData(blogType.page(startIndex, pageCount));
        return pageBean;
    }

dao层

public List<BlogType> page(int currentPage,int pageCount){
        String sql = "select * from t_blogtype limit ?,?";
        PageBean<BlogType> pageBean =null;
        Connection conn =null;
        PreparedStatement ps =null;
        ResultSet rs =null;
        BlogType blogType =null;
        try {
            conn =DBDao.connection();
            ps=conn.prepareStatement(sql);
            ps.setInt(1, currentPage);
            ps.setInt(2, pageCount);
            rs=ps.executeQuery();
            List<BlogType> list =new ArrayList<BlogType>();
            while(rs.next()){
                blogType = new BlogType();
                blogType.setId(rs.getInt("id"));
                blogType.setTypeName(rs.getString("typeName"));
                blogType.setOrderNum(pageCount);
                list.add(blogType);
            }
            return list;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    public int getTotal() {
        String sql ="select count(id) from t_blogtype";
        Connection conn =null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        int count=0;
        try{
            conn= DBDao.connection();
            ps=conn.prepareStatement(sql);
            rs=ps.executeQuery();
            rs.next();
            count=rs.getInt(1);

        }catch(Exception e){
            e.printStackTrace();
        }
        return count;  

    }

　　因为本文主要在说分页查询，所以关于 数据库的连接就一并放到dao里了！

　　（其实本人是不知道将数据库的连接放在哪里。。。。嘻嘻）

jsp

 <body>
     共有${page.totalCount }个分类,共有${page.pageCount }页，当前为第${page.currentPage }页，每页显示${page.pageCount }条
     <table align="center" width="100%">
         <thead>
             <th>选择</th>
             <th>序号</th>
             <th>博客类别</th>
             <th>博客排序</th>
             <th>操作</th>
         </thead>
         <tbody align="center" border="1">
             <c:forEach items="${page.pageData }" var="page">
                 <tr>
                 <td><input  type="checkbox" name="id"/></td>
                 <td>${page.id }</td>
                 <td>${page.typeName }</td>
                 <td>${page.orderNum }</td>
                 <td><a>修改</a>|<a>删除</a></td>
                 <td></td>
             </tr>
             </c:forEach>
         </tbody>

     </table>
     <!-- 分页 -->
     <div style="text-align:center;">
         <a href="${pageContext.request.contextPath }/blogType?currentPage=1">首页</a>
         <!-- 如果当前页为第一页，就没有上一页这个标签 -->
         <c:if test="${page.currentPage==1 }">
             <c:forEach begin="${page.start }" end="${page.end }" step="1" var="i">
                 <c:if test="${page.currentPage == i}">
                         ${i}
                 </c:if>
                 <c:if test="${page.currentPage != i}">
                         <a href="${pageContext.request.contextPath}/blogType?currentPage=${i}">${i}</a>
                  </c:if>
             </c:forEach>
             <a href="${pageContext.request.contextPath }/blogType?currentPage=${page.currentPage+1}">下一页</a>
         </c:if>
         <!-- 如果不是首页也不是尾页，就与上一页和下一页 -->
         <c:if test="${page.currentPage>1 && page.currentPage<page.totalPage }">
             <a href="${pageContext.request.contextPath }/blogType?currentPage=${page.currentPage-1}">上一页</a>
             <c:forEach begin="${page.start }" end="${page.end }" step="1" var="i">
                 <c:if test="${page.currentPage == i}">
                         ${i}
                 </c:if>
                 <c:if test="${page.currentPage != i}">
                         <a href="${pageContext.request.contextPath}/blogType?currentPage=${i}">${i}</a>
                  </c:if>
             </c:forEach>
             <a href="${pageContext.request.contextPath }/blogType?currentPage=${page.currentPage+1}">下一页</a>
         </c:if>
         <!-- 如果是最后一页，则没有下一页 -->
         <c:if test="${page.currentPage==page.totalPage }">
             <a href="${pageContext.request.contextPath }/blogType?currentPage=${page.currentPage-1}">上一页</a>
             <c:forEach begin="${page.start }" end="${page.end }" step="1" var="i">
                 <c:if test="${page.currentPage == i}">
                         ${i}
                 </c:if>
                 <c:if test="${page.currentPage != i}">
                         <a href="${pageContext.request.contextPath}/blogType?currentPage=${i}">${i}</a>
                  </c:if>
             </c:forEach>

         </c:if>
         <a href="${pageContext.request.contextPath }/blogType?currentPage=${page.totalPage}">尾页</a>
     </div>

 </body>