分页操作

1、一般先封装一个用来显示分页的vo类

public class PageBean<T> {
    
    //当前页
    private int currentPage;
    //当前页显示的条数
    private int currentCount;
    //总条数
    private int totalCount;
    //总页数
    private int totalPage;
    //每页显示的数据
    private List<T> productList = new ArrayList<T>();
    
    
    public int getCurrentPage() {
        return currentPage;
    }
    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }
    public int getCurrentCount() {
        return currentCount;
    }
    public void setCurrentCount(int currentCount) {
        this.currentCount = currentCount;
    }
    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 List<T> getProductList() {
        return productList;
    }
    public void setProductList(List<T> productList) {
        this.productList = productList;
    }

}

Jsp

<!--分页 -->
    <div style=" 380px; margin: 0 auto; margin-top: 50px;">
        <ul class="pagination" style="text-align: center; margin-top: 10px;">
            <!-- 上一页 -->
            <!-- 判断当前页是否是第一页 -->
            <c:if test="${pageBean.currentPage==1 }">
                <li class="disabled">
                    <a href="javascript:void(0);" aria-label="Previous">
                        <span aria-hidden="true">&laquo;</span>
                    </a>
                </li>
            </c:if>
            <c:if test="${pageBean.currentPage!=1 }">
                <li>
                    <a href="${pageContext.request.contextPath }/productList?currentPage=${pageBean.currentPage-1}" aria-label="Previous">
                        <span aria-hidden="true">&laquo;</span>
                    </a>
                </li>
            </c:if>    

            <!-- 开始分页 -->
            <c:forEach begin="1" end="${pageBean.totalPage }" var="page">
                <!-- 判断当前页 -->
                <c:if test="${pageBean.currentPage==page }">
                    <li class="active"><a href="javascript:void(0);">${page}</a></li>
                </c:if>
                <c:if test="${pageBean.currentPage!=page }">
                    <li><a href="${pageContext.request.contextPath }/productList?currentPage=${page}">${page}</a></li>
                </c:if>
            
            </c:forEach>
            
            <!-- 判断当前页是否是最后一页 -->
            <c:if test="${pageBean.currentPage==pageBean.totalPage }">
                <li class="disabled">
                    <a href="javascript:void(0);" aria-label="Next"> 
                        <span aria-hidden="true">&raquo;</span>
                    </a>
                </li>
            </c:if>
            <c:if test="${pageBean.currentPage!=pageBean.totalPage }">
                <li>
                    <a href="${pageContext.request.contextPath }/productList?currentPage=${pageBean.currentPage+1}" aria-label="Next"> 
                        <span aria-hidden="true">&raquo;</span>
                    </a>
                </li>
            </c:if>
        <!-- 当点击下一页或者通过数字锁定页数的时候要传到后台你想跳的页码 -->
        </ul>
    </div>
 <!-- 分页结束 -->

Servlet

//获得你想跳的页码 如果第一次访问列表，则currentPageStr为空，默认第一页
String currentPageStr = request.getParameter("currentPage");
if(currentPageStr==null) currentPageStr="1";
int currentPage = Integer.parseInt(currentPageStr);
//默认每页显示12条
int currentCount = 12;

PageBean<Product> pageBean = null;
try {
    pageBean = service.findPageBean(currentPage,currentCount);
} catch (SQLException e) {
    e.printStackTrace();
}

request.setAttribute("pageBean", pageBean);

request.getRequestDispatcher("/product_list.jsp").forward(request, response);

Service

//分页操作
public PageBean findPageBean(int currentPage,int currentCount) throws SQLException  {

    ProductDao dao = new ProductDao();
    
    //目的：就是想办法封装一个PageBean 并返回
    PageBean pageBean = new PageBean();
    //1、当前页 currentPage;
    pageBean.setCurrentPage(currentPage);
    //2、当前页显示的条数 currentCount;
    pageBean.setCurrentCount(currentCount);
    //3、总条数 totalCount;
    int totalCount = dao.getTotalCount();
    pageBean.setTotalCount(totalCount);
    //4、总页数 totalPage;
    /*
     * 总条数        当前页显示的条数    总页数
     * 10                 4             3
     * 11                 4             3
     * 12                 4             3
     * 13                 4             4
     * 
     * 公式：总页数=Math.ceil(总条数/当前显示的条数)
     * 
     */
    int totalPage = (int) Math.ceil(1.0*totalCount/currentCount);
    pageBean.setTotalPage(totalPage);
    //5、每页显示的数据private List<T> productList = new ArrayList<T>();
    /*
     * 页数与limit起始索引的关系
     * 例如 每页显示4条
     * 页数        起始索引        每页显示条数
     * 1              0               4
     * 2              4               4
     * 3              8               4
     * 4              12              4
     * 
     * 索引index = (当前页数-1)*每页显示的条数
     * 
     */
    int index = (currentPage-1)*currentCount;
    
    List<Product> productList = dao.findProductListForPageBean(index,currentCount);
    pageBean.setProductList(productList);
    
    return pageBean;
}

Dao

//获得全部的商品条数
public int getTotalCount() throws SQLException {
    QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
    String sql = "select count(*) from product";
    Long query = (Long) runner.query(sql, new ScalarHandler());
    return query.intValue();
}

//获得分页的商品数据
public List<Product> findProductListForPageBean(int index,int currentCount) throws SQLException {
    QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
    String sql = "select * from product limit ?,?";
    return runner.query(sql, new BeanListHandler<Product>(Product.class), index,currentCount);
}

另一种封装PageBean的方法

public class PageBean {

    private Integer currentPage;
    private Integer pageSize;
    private Integer totalCount;
    private Integer totalPage;
    private List list;
    
    public PageBean(Integer currentPage, Integer pageSize, Integer totalCount) {
        
        this.currentPage = currentPage;
        this.pageSize = pageSize;
        this.totalCount = totalCount;
        
        if(this.currentPage == null){
            this.currentPage = 1;
        }
        
        if(this.pageSize == null){
            this.pageSize = 3;
        }
        
        this.totalPage = (this.totalCount+this.pageSize-1)/this.pageSize;
        
        if(this.currentPage < 1){
            this.currentPage = 1;
        }
        
        if(this.currentPage > this.totalPage){
            this.currentPage = this.totalPage;
        }
    }
    
    public int getStart(){
        return (this.currentPage-1)*this.pageSize;
    }
    
    public Integer getCurrentPage() {
        return currentPage;
    }
    public void setCurrentPage(Integer currentPage) {
        this.currentPage = currentPage;
    }
    public Integer getPageSize() {
        return pageSize;
    }
    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }
    public Integer getTotalCount() {
        return totalCount;
    }
    public void setTotalCount(Integer totalCount) {
        this.totalCount = totalCount;
    }
    public Integer getTotalPage() {
        return totalPage;
    }
    public void setTotalPage(Integer totalPage) {
        this.totalPage = totalPage;
    }
    public List getList() {
        return list;
    }
    public void setList(List list) {
        this.list = list;
    }
    
}