java 高级查询

一.概述

       对于java中,前端对于多条件的查询,往往参数过多,如果后端在接收参数的时候不进行封装,会使得代码重复率高,代码累赘,进行一定的封装和抽取,会大大提高代码的简洁和可维护性.

二.高级查询的封装示例

   1.数据库建表

DROP TABLE IF EXISTS `product`;
CREATE TABLE `product` (
  `id` bigint(11) NOT NULL AUTO_INCREMENT,
  `productName` varchar(50) DEFAULT NULL,
  `dir_id` bigint(11) DEFAULT NULL,
  `salePrice` decimal(10,2) DEFAULT NULL,
  `supplier` varchar(50) DEFAULT NULL,
  `brand` varchar(50) DEFAULT NULL,
  `cutoff` double(2,2) DEFAULT NULL,
  `costPrice` decimal(10,2) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `dir_id` (`dir_id`),
  CONSTRAINT `product_ibfk_1` FOREIGN KEY (`dir_id`) REFERENCES `productdir` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=21 DEFAULT CHARSET=utf8;

DROP TABLE IF EXISTS `productdir`;
CREATE TABLE `productdir` (
  `id` bigint(11) NOT NULL AUTO_INCREMENT,
  `dirName` varchar(30) DEFAULT NULL,
  `parent_id` bigint(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

 2.javaBean

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Product {
	private Long id; // 商品编号
	private String productName; // 商品名称
	private Long dir_id; //商品分类
	private BigDecimal salePrice; // 售价
	private String supplier; // 供应商
	private String brand; // 商标
	private Double cutoff; // 折价
	private BigDecimal costPrice; // 成本价
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public class ProductDir {
	private Long id; //商品分类编号
	private String dirName; //分类名称
	private Long parent_id; // 分类的父分类
}

 3.封装查询对象

//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<>();
	
	// 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));
	}

}

@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
							+ "%");
		}
	}

}

@Data
public class ProductDirQueryObject extends QueryObject {
	private String name;

	// 获取查询的条件和参数,自定义的查询方法
	protected void customizedQuery() {
		if (StringUtil.hasLength(name)) {
			super.addQuery(" dirName LIKE ?", "%" + name + "%");
		}
	}


}

4.Serverlet

@WebServlet("/product")
public class ProductServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	// 商品的dao对象
	private IProductDAO productDao;
	// 商品分类dao对象
	private IProductDirDAO productDirDao;
    @Override
	public void init() throws ServletException {
		productDao = new ProductDAOImpl();
		productDirDao = new ProductDirDAOImpl();
	}

   protected void list1(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		ProductQueryObject qo = getProductQueryObject(req);
		
		List<Product> list = productDao.query(qo);
		List<ProductDir> dirList = productDirDao.list();
		req.setAttribute("list", list);
		req.setAttribute("dirList", dirList);
		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);
		}
		
		return qo;
	}
}

5.前端页面

<%@ 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>
	<a href="${pageContext.request.contextPath}/product?cmd=edit">添加货品</a>
	<!-- 高级查询  开始-->
	<form action="/product" method="post">
		<input name="currentPage" id="currentPage" value="" type="hidden" />
		商品的名称:<input name="productName" value="${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>
		
		</table>
				
	</form>

</body>
</html>