java 分页查询

一.概述

      在上一篇高级查询中,已经对查询对象进行了封装,在本篇文章中,主要来分析分页的封装和分页和高级查询的合并.

     1. 真分页:

          物理分页:每次翻页都从数据库中查询              优点:不会造成内存溢出     缺点:翻页的速度比较慢

    2.假分页:

        逻辑分页:一次性将所有的数据查询出来,放在内存中             优点:分页的速度比较快    缺点:可能造成内存溢出

二.分页对象的封装

@Data
//分页的结果对象
public class PageResult {
	// 结果集数据
	private List listData;
	// 总条数
	private Integer totalCount;
	// 当前页
	private Integer currentPage;
	// 总页数
	private Integer totalPage;
	// 上一页
	private Integer prePage;
	// 下一页
	private Integer nextPage;
	// 页面大小
	private Integer pageSize;
	// 首页
	private Integer beginPage = 1;

	private PageIndex pageIndex;

	public PageResult() {
	}

	public PageResult(List listData, Integer totalCount, Integer currentPage,
			Integer pageSize) {
		this.listData = listData;
		this.totalCount = totalCount;
		this.currentPage = currentPage;
		this.pageSize = pageSize;
		// 计算的数据
		this.totalPage = this.totalCount % this.pageSize == 0 ? this.totalCount
				/ this.pageSize : this.totalCount / this.pageSize + 1;
		this.prePage = this.currentPage - 1 >= 1 ? this.currentPage - 1 : 1;
		this.nextPage = this.currentPage + 1 <= this.totalPage ? this.currentPage + 1
				: this.totalPage;
		// 创建PageIndex的对象
		this.pageIndex = PageIndex.getPageIndex(5, currentPage, totalPage);
	}

	
}


// 分页算法对象
@Data
public class PageIndex {
	private Integer beginIndex;
	private Integer endIndex;

	/**
	 * 首页 上页 [1] 2 3 4 5 6 7 8 9 10 下页 末页 当前第1/18页一共53条记录 每页5 条
	 * @param totalIndexCount	总索引数
	 * @param currentPage		当前页
	 * @param totalPage			总页数
	 * @return
	 */
	public static PageIndex getPageIndex(Integer totalIndexCount,
			Integer currentPage, Integer totalPage) {
		Integer startPageIndex = currentPage
				- (totalIndexCount % 2 == 0 ? totalIndexCount / 2 - 1
						: totalIndexCount / 2);
		Integer endPageIndex = currentPage + totalIndexCount / 2;
		if (startPageIndex < 1) {
			startPageIndex = 1;
			if (totalPage >= totalIndexCount)
				endPageIndex = totalIndexCount;
			else
				endPageIndex = totalPage;
		}
		if (endPageIndex > totalPage) {
			endPageIndex = totalPage;
			if ((endPageIndex - totalIndexCount) > 0)
				startPageIndex = endPageIndex - totalIndexCount + 1;
			else
				startPageIndex = 1;
		}
		return new PageIndex(startPageIndex, endPageIndex);
	}

	public PageIndex(Integer beginIndex, Integer endIndex) {
		this.beginIndex = beginIndex;
		this.endIndex = endIndex;
	}

	
}

三.查询对象的封装

@Data
public class ProductQueryObject extends QueryObject {
	private String productName;
	private BigDecimal minSalePrice;
	private BigDecimal maxSalePrice;
	// 商品分类的编号
	private Long dir_id;
	// 关键字 商品的名称/品牌/供应商
	private String keyword;
	

	// 获取查询的条件和参数,自定义的查询方法
	protected void customizedQuery() {
		if (StringUtil.hasLength(productName)) {
			super.addQuery(" productName LIKE ?", "%" + productName + "%");
		}
		if (minSalePrice != null) {
			super.addQuery(" salePrice >=?", minSalePrice);
		}
		if (maxSalePrice != null) {
			super.addQuery(" salePrice <=?", maxSalePrice);
		}
		if (dir_id != null && dir_id != -1L) {
			super.addQuery(" dir_id =?", dir_id);
		}
		if (StringUtil.hasLength(keyword)) {
			super.addQuery(
					" productName LIKE ? OR brand LIKE ? OR supplier LIKE ?",
					"%" + keyword + "%", "%" + keyword + "%", "%" + keyword
							+ "%");
		}
	}
	
}


//公用的查询对象
@Data
public class QueryObject {
	// 存放sql的条件
	private List<String> conditions = new ArrayList<>();
	// 存放sql中的参数的值
	private List<Object> params = new ArrayList<>();
	private Integer currentPage;;
	private Integer pageSize;
	// 拼接sql语句
	public String getQuery() {
		StringBuilder sb = new StringBuilder();
		customizedQuery();
		// 拼接sql
		for (int i = 0; i < conditions.size(); i++) {
			if (i == 0) {
				sb.append(" WHERE ");
			} else {
				sb.append(" AND ");
			}
			sb.append(conditions.get(i));
		}
		return sb.toString();
	}
	// 专门暴露给子类实现
	protected void customizedQuery() {
	}
	//将子类中的条件和参数传递给当前类中的对应的集合
	protected void addQuery(String condition, Object... params) {
		//当有多个条件的时候,应该在条件前后加上()
		if(params.length>1){
			this.conditions.add("("+condition+")");
		}else{
			this.conditions.add(condition);
		}
		this.params.addAll(Arrays.asList(params));
	}

}

四.serverlet封装

@WebServlet("/product")
public class ProductServlet extends HttpServlet {
    	protected void list(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		ProductQueryObject qo = getProductQueryObject(req);
		// 获取分页对象的数据
		PageResult page = productDao.pageQuery(qo);
		req.setAttribute("page", page);
		req.setAttribute("qo", qo);
		req.getRequestDispatcher("/WEB-INF/views/product/list.jsp").forward(
				req, resp);
	}

	// 封装查询对象
	private ProductQueryObject getProductQueryObject(HttpServletRequest req) {
		// 获取请求参数
		String productName = req.getParameter("productName");
		String minSalePrice = req.getParameter("minSalePrice");
		String maxSalePrice = req.getParameter("maxSalePrice");
		String dir_id = req.getParameter("dir_id");
		String keyword = req.getParameter("keyword");
		String currentPage = req.getParameter("currentPage");
		String pageSize = req.getParameter("pageSize");
		// 默认的页面
		Integer iCurrentPage = 1;
		// 默认的页面大小
		Integer iPageSize = 3;
		if (StringUtil.hasLength(currentPage)) {
			iCurrentPage = Integer.valueOf(currentPage);
		}
		if (StringUtil.hasLength(pageSize)) {
			iPageSize = Integer.valueOf(pageSize);
		}
		// 封装查询对象
		ProductQueryObject qo = new ProductQueryObject();
		qo.setProductName(productName);
		if (StringUtil.hasLength(minSalePrice)) {
			qo.setMinSalePrice(new BigDecimal(minSalePrice));
		}
		if (StringUtil.hasLength(maxSalePrice)) {
			qo.setMaxSalePrice(new BigDecimal(maxSalePrice));
		}
		if (StringUtil.hasLength(dir_id)) {
			qo.setDir_id(Long.valueOf(dir_id));
		}
		if (StringUtil.hasLength(keyword)) {
			qo.setKeyword(keyword);
		}
		qo.setCurrentPage(iCurrentPage);
		qo.setPageSize(iPageSize);
		return qo;
	}
}

五.dao查询的封装

public class BaseDAO {

	public PageResult query(QueryObject qo,String tableName,Class clz) {
		// 获取商品的结果集
		String sql = "SELECT * FROM "+tableName+" " + qo.getQuery() + " limit ?,?";
		// 获取高级查询的参数
		List<Object> params = qo.getParams();
		Integer beginIndex = (qo.getCurrentPage() - 1) * qo.getPageSize();
		// 重新创建一个新的集合,用来存放高级查询的数据和分页的数据
		List<Object> newParams = new ArrayList<>();
		newParams.addAll(params);
		newParams.add(beginIndex);
		newParams.add(qo.getPageSize());
		List listData = JdbcTemplate.query(sql,
				new BeanListHandler(clz),
				newParams.toArray());
		// 获取总条数
		Integer totalCount = JdbcTemplate.query(
				"Select count(*) FROM "+tableName+" "+ qo.getQuery(),
				new IResultSetHandler<Long>() {

					@Override
					public Long handle(ResultSet rs) {
						try {
							if (rs.next()) {
								return rs.getLong(1);
							}
						} catch (SQLException e) {
							e.printStackTrace();
						}
						return 0L;
					}
				}, qo.getParams().toArray()).intValue();

		PageResult result = new PageResult(listData, totalCount,
				qo.getCurrentPage(), qo.getPageSize());
		return result;
	}
}

// 商品类的规范
public interface IProductDAO {
    /**
	 * 高级查询+分页
	 * @param qo 高级查询的数据和分页的数据
	 * @return 返回分页之后的结果
	 */
	PageResult pageQuery(ProductQueryObject qo);
}

public class ProductDAOImpl extends BaseDAO implements IProductDAO {
    @Override
	public PageResult pageQuery(ProductQueryObject qo) {
		return super.query(qo,"product",Product.class);
	}
}

六.前端的页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>货品显示列表</title>

<!-- 新 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet"
	href="/bootstrap/bootstrap.min.css">

<!-- 可选的Bootstrap主题文件（一般不用引入） -->
<link rel="stylesheet"
	href="/bootstrap/bootstrap-theme.min.css">

<!-- jQuery文件。务必在bootstrap.min.js 之前引入 -->
<script src="/bootstrap/jquery.min.js"></script>

<!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
<script src="/bootstrap/bootstrap.min.js"></script>
<script type="text/javascript">
	function go(currentPage) {
		//将当前页的数据设置给currentPage隐藏域
		document.getElementById("currentPage").value = currentPage;
		//提交表单
		document.forms[0].submit();
	}
</script>
</head>
<body>
<marquee direction="right" >

	<a href="${pageContext.request.contextPath}/product?cmd=edit">添加货品</a>
</marquee>
	<!-- 高级查询  开始-->
	<form action="${pageContext.request.contextPath}/product" method="post">
		<input name="currentPage" id="currentPage" value="" type="hidden" />
		商品的名称:<input name="productName" value="${qo.productName}" /> 商品零售价:<input
			type="number" name="minSalePrice" value="${qo.minSalePrice}" /> -<input
			type="number" name="maxSalePrice" value="${qo.maxSalePrice}" />
		商品分类:<select name="dir_id">
			<option value='-1'>..请选择...</option>
			<c:forEach items="${dirList}" var="dir">
				<option value='${dir.id}'
					${qo.dir_id==dir.id?'selected=selected':''}>${dir.dirName}</option>
			</c:forEach>
		</select> 关键字:<input name="keyword" placeholder="名称/品牌/供应商"
			value="${qo.keyword}" /> <input type="submit" value="查询" /> <input
			type="reset" value="重置" />
	</form>
	<!-- 高级查询 结束-->
	<form action="${pageContext.request.contextPath}/product" method="post" id="form2">
		<table border="1" cellpadding="0" cellspacing="0" width="90%">
			<tr>
				<th>货品编号</th>
				<th>货品名称</th>
				<th>货品品牌</th>
				<th>货品分类</th>
				<th>供&nbsp;应&nbsp;商</th>
				<th>零&nbsp;售&nbsp;价</th>
				<th>成&nbsp;本&nbsp;价</th>
				<th>折&emsp;&emsp;扣</th>
				<th>操&emsp;&emsp;作</th>
			</tr>
			<c:if test="${empty page.listData}">
				<tr>
					<td colspan="9" style="text-align: center; color: red;">亲,没有查询到您需要的数据~~~</td>
				</tr>
			</c:if>
			<c:forEach items="${page.listData}" var="pro" varStatus="vs">
				<tr>
					<td>${pro.id}</td>
					<td>${pro.productName}</td>
					<td>${pro.brand}</td>
					<td>${pro.dir_id}</td>
					<td>${pro.supplier}</td>
					<td>${pro.salePrice}</td>
					<td>${pro.costPrice}</td>
					<td>${pro.cutoff}</td>
					<td><a href="/product?cmd=edit&id=${pro.id}">编辑</a> | <a
						href="${pageContext.request.contextPath}/product?cmd=delete&id=${pro.id}">删除</a>
					</td>
				</tr>
			</c:forEach>
			<tr>
				<td colspan="9" >
					<a href="${pageContext.request.contextPath}/product?currentPage=1" >首页</a>
					<a href="javascript:go(${page.prePage })" >上一页</a>
					<c:forEach begin="${page.pageIndex.beginIndex }" end="${page.pageIndex.endIndex }" var="index" >
						<c:if test="${page.currentPage == index }">
							${index }
						</c:if>
						<c:if test="${page.currentPage != index }">
							<a href="${pageContext.request.contextPath}/product?currentPage=${index }">${index }</a>
						</c:if>
					</c:forEach>
					
					<a href="javascript:go(${page.nextPage })" >下一页</a>
					<a href="${pageContext.request.contextPath}/product?currentPage=${page.totalPage }" >尾页</a>
					总条数:${ page.totalCount}
					当前页:${ page.currentPage}/${ page.totalPage}
					<input type="number" name="currentPage" style="width:50px" min="1" max="${page.totalPage}" value="${ page.currentPage}" />
					<input type="submit" value="go" />
					每页显示<select name="pageSize" onchange="document.getElementById('form2').submit()" >
								<option ${page.pageSize==5?'selected=selected':'' } >5</option>
								<option ${page.pageSize==10?'selected=selected':'' }>10</option>
								<option ${page.pageSize==15?'selected=selected':'' }>15</option>
						 </select>条
				</td>
			</tr>
		</table>		
	</form>
</body>
</html>