JAVAWEB学习笔记21

Posted 2020-09-20 杨铭宇

今天主要学习了数据库的多条件查询、attr和prop的区别和分页的实现

一、实现多条件查询

public List<Product> findProductListByCondition(Condition condition) throws SQLException {
    QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
    //定义一个存储实际参数的容器
    List<String> list = new ArrayList<String>();
    String sql = "select * from product where 1=1";
    if(condition.getPname()!=null&&!condition.getPname().trim().equals("")){
        sql+=" and pname like ? ";
        list.add("%"+condition.getPname().trim()+"%");
    }
    if(condition.getIsHot()!=null&&!condition.getIsHot().trim().equals("")){
        sql+=" and is_hot=? ";
        list.add(condition.getIsHot().trim());
    }
    if(condition.getCid()!=null&&!condition.getCid().trim().equals("")){
        sql+=" and cid=? ";
        list.add(condition.getCid().trim());
    }
    
    List<Product> productList = runner.query(sql, new BeanListHandler<Product>(Product.class) , list.toArray());
    
    return productList;
}

 

二、jquery中attr和prop的区别

 

在高版本的jquery引入prop方法后，什么时候该用prop？什么时候用attr？它们两个之间有什么区别？这些问题就出现了。

 

关于它们两个的区别，网上的答案很多。这里谈谈我的心得，我的心得很简单：

 

• 对于html元素本身就带有的固有属性，在处理时，使用prop方法。
• 对于HTML元素我们自己自定义的DOM属性，在处理时，使用attr方法。

 

attr和prop的区别我是通过这个了解到的：http://www.cnblogs.com/Showshare/p/different-between-attr-and-prop.html

 

三、分页的实现：

1、创建一个PageBean用于存储分页的数据

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;
    }
    
}

2、WEB层代码

 

public class ProductListServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        ProductService service = new ProductService();
        
        //模拟当前是第一页
        String currentPageStr = request.getParameter("currentPage");
        if(currentPageStr==null) currentPageStr="1";
        int currentPage = Integer.parseInt(currentPageStr);
        //认为每页显示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);
        
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

 

 

 

3、Service层代码

 

public class ProductService {

    public List<Product> findAllProduct() throws SQLException {
        ProductDao dao = new ProductDao();
        return dao.findAllProduct();
    }

    //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private int currentPage;
        pageBean.setCurrentPage(currentPage);
        //2、当前页显示的条数private int currentCount;
        pageBean.setCurrentCount(currentCount);
        //3、总条数private int totalCount;
        int totalCount = dao.getTotalCount();
        pageBean.setTotalCount(totalCount);
        //4、总页数private int 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        其实索引        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;
    }

}

 

 

 

4、DAO层代码

 

public class ProductDao {

    public List<Product> findAllProduct() throws SQLException {
        return new QueryRunner(DataSourceUtils.getDataSource()).query("select * from product", new BeanListHandler<Product>(Product.class));
    }

    //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);
    }

}

 

 

 

5、JSP页面代码

 

<div class="row" style="width: 1210px; margin: 0 auto;">
        <div class="col-md-12">
            <ol class="breadcrumb">
                <li><a href="#">首页</a></li>
            </ol>
        </div>
        
        <c:forEach items="${pageBean.productList }" var="product">
            <div class="col-md-2" style="height:250px">
                <a href="product_info.htm"> 
                    <img src="${pageContext.request.contextPath }/${product.pimage}" width="170" height="170" style="display: inline-block;">
                </a>
                <p>
                    <a href="product_info.html" style=\'color: green\'>${product.pname }</a>
                </p>
                <p>
                    <font color="#FF0000">商城价：&yen;${product.shop_price }</font>
                </p>
            </div>
        </c:forEach>

    </div>

    <!--分页 -->
    <div style="width: 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>    
            
            
            
        
            <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>
        
        </ul>
    </div>
    <!-- 分页结束 -->