MyBatis简易教程

数据库

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MyBatis简易教程欢迎进入MyBatis简易教程。本教程旨在帮助您快速入门MyBatis，并掌握其基本用法。通过本教程，您将了解MyBatis的核心概念、配置方法以及如何在项目中集成和使用MyBatis进行数据库操作。 1. MyBatis简介 MyBatis是一款优秀的持久层框架，它通过消除几乎所有的JDBC代码和手动设置参数以及检索结果集的工作，让开发者专注于SQL本身。MyBatis支持自定义SQL、存储过程以及高级映射。它极大的简化了数据库操作，并与现有的Java代码完美集成。 2. 环境准备在开始使用MyBatis之前，您需要准备以下开发环境： JDK 8或以上版本 Maven或Gradle构建工具数据库（如MySQL、Oracle等）

package cn.edu.guet; import java.sql.Date; import java.text.SimpleDateFormat; import java.util.HashMap; import java.util.Map; /** * @Author liwei * @Date 2023/1/8 17:26 * @Version 1.0 */ public class Test { public static void main(String[] args) { String employee_id = null; String first_name = null; String last_name = "JACK"; String email = null; String phone_number = "18076"; String hire_date = null; SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); Date hireDate = null; if (hire_date != null) { hireDate = Date.valueOf(hire_date); } try { Map map = new HashMap(); int count = 1; String sql = "SELECT * FROM employees"; String whereClause = ""; StringBuffer sb = new StringBuffer(); sb.append(sql); StringBuffer where = new StringBuffer(); if (employee_id != null && !"".equals(employee_id)) { if (whereClause.equals("")) { where.append(" WHERE employee_id=?"); whereClause = where.toString(); } else { where.append(" AND employee_id=?"); whereClause = where.toString(); } map.put(count++, employee_id); } if (first_name != null && !"".equals(first_name)) { if (whereClause.equals("")) { where.append(" WHERE first_name LIKE ?"); whereClause = where.toString(); } else { where.append(" AND first_name LIKE ?"); whereClause = where.toString(); } map.put(count++, first_name); } if (last_name != null && !"".equals(last_name)) { if (whereClause.equals("")) { where.append(" WHERE last_name LIKE ?"); whereClause = where.toString(); } else { where.append(" AND last_name LIKE ?"); whereClause = where.toString(); } map.put(count++, last_name); } if (email != null && !"".equals(email)) { if (whereClause.equals("")) { where.append(" WHERE email LIKE ?"); whereClause = where.toString(); } else { where.append(" AND email LIKE ?"); whereClause = where.toString(); } map.put(count++, email); } if (phone_number != null && !"".equals(phone_number)) { if (whereClause.equals("")) { where.append(" WHERE phone_number LIKE ?"); whereClause = where.toString(); } else { where.append(" AND phone_number LIKE ?"); whereClause = where.toString(); } map.put(count++, phone_number); } if (hire_date != null && !"".equals(hire_date)) { if (whereClause.equals("")) { where.append(" WHERE hire_date=?"); whereClause = where.toString(); } else { where.append(" AND hire_date=?"); whereClause = where.toString(); } map.put(count++, hireDate); } sb.append(where.toString()); sql = sb.toString(); System.out.println("SQL语句是：" + sql); } catch (Exception e) { e.printStackTrace(); } } @Override public List searchBill(PlanDesignDTO planDesignDTO) throws SQLException { String sql = "SELECT * FROM PlanDesignInfo"; String whereClause = ""; StringBuffer sb = new StringBuffer(); sb.append(sql); StringBuffer where = new StringBuffer(); //把所有的值存储起来 Map map = new TreeMap(); int count = 1; if (!StringUtils.isBlank(planDesignDTO.getPlanDesignName())) { if (whereClause.equals("")) { where.append(" WHERE plan_design_name LIKE ?"); whereClause = where.toString(); } else { where.append(" AND plan_design_name LIKE ?"); whereClause = where.toString(); } map.put(count++, planDesignDTO.getPlanDesignName()); } if (planDesignDTO.getSpecId() != null) { if (whereClause.equals("")) { where.append(" WHERE spec_id=?"); whereClause = where.toString(); } else { where.append(" AND spec_id=?"); whereClause = where.toString(); } map.put(count++, planDesignDTO.getSpecId()); } if (!StringUtils.isBlank(planDesignDTO.getDesigner())) { if (whereClause.equals("")) { where.append(" WHERE designer LIKE ?"); whereClause = where.toString(); } else { where.append(" AND designer LIKE ?"); whereClause = where.toString(); } map.put(count++, planDesignDTO.getDesigner()); } if (CollectionUtil.isNotEmpty(planDesignDTO.getDesignTime())) { if (whereClause.equals("")) { where.append(" WHERE create_time between ? AND ?"); whereClause = where.toString(); } else { where.append(" AND create_time between ? AND ?"); whereClause = where.toString(); } map.put(count++, planDesignDTO.getDesignTime()); } sb.append(whereClause); sql = sb.toString(); Connection conn = DBConnection.getConn(); PreparedStatement pstmt = conn.prepareStatement(sql); /* 给占位符赋值 */ Set keySet = map.keySet(); Iterator iterator = keySet.stream().iterator(); while (iterator.hasNext()) { Integer key = iterator.next(); if (ClassUtils.isAssignable(map.get(key).getClass(), String.class)) { pstmt.setObject(key, "%" + map.get(key) + "%"); } else { pstmt.setObject(key, map.get(key)); } } ResultSet rs = pstmt.executeQuery(); while (rs.next()) { /* 把查询到的数据封装成PlanDesignInfo类，并且返回 */ System.out.println(rs.getString("plan_design_name")); } return null; } }