MyBatis介绍：

​ mybatis 是一个优秀的基于 java 的持久层框架，它内部封装了 jdbc，使开发者只需要关注 sql 语句本身，而不需要花费精力去处理加载驱动、创建连接、创建 statement 等繁杂的过程。

​ mybatis 通过xml 或注解的方式将执行的各种statement 配置起来，并通过java 对象和statement 中sql的动态参数进行映射生成最终执行的 sql 语句，最后由 mybatis 框架执行 sql并将结果映射为 java 对象并返回。
采用 ORM ( Object relational mapping)思想解决了实体和数据库映射的问题，对jdbc 进行了封装，屏蔽了jdbc api 底层访问细节，使我们不用与 jdbc api打交道，就可以完成对数据库的持久化操作。

ORM ( Object relational mapping)：对象关系映射 javabean–关系型数据库MySQL

​ 通过ORM解决sql语句执行结果映射为java对象 【表中字段–javabean属性 自动完成映射 就要求查询返回的字段和javabean的属性一致。】

​ 官网: http://www.mybatis.org/mybatis-3/

接下来使用MyBatis实现CURD：

环境准备：

添加依赖
pom.xml配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.Mr_Xu</groupId><artifactId>dya34</artifactId><version>1.0-SNAPSHOT</version><!--JDK编译版本设置--><properties><project.build.sourcEncoding>UTF-8</project.build.sourcEncoding><maven.compiler.source>1.8</maven.compiler.source><maven.compiler.target>1.8</maven.compiler.target></properties><!--1. 添加依赖--><dependencies><!--单元测试--><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency><!--MyBatis坐标--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.4.6</version></dependency><!--mysql驱动--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.47</version></dependency><!--lombok 依赖--><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.18</version></dependency></dependencies>
</project>

mybatis核心文件配置：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--MyBatis的核心配置文件 configuration就是根标签-->
<configuration><typeAliases><!--方式一：单个设置--><typeAlias type="com.Mr_Xu.bean.User" alias="User"></typeAlias><!--方式二：批量设置 【推荐】--><!--<package name="com.itheima.bean"/>--></typeAliases><!--数据库环境配置--><environments default="development"><environment id="development"><!--MyBatis的事务管理 采用的是JDBC事务控制--><transactionManager type="JDBC"/><!--MyBatis连接池配置 使用MyBatis默认的POOLED--><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/dya34_mybatis"/><property name="username" value="root"/><property name="password" value="toor"/></dataSource></environment></environments><!--mappers就对应dao接口映射文件--><!--引入dao接口映射文件--><mappers><mapper resource="com/Mr_Xu/dao/UserDao.xml" /></mappers></configuration>

User实体类：

package com.Mr_Xu.bean;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.util.Date;/*** @Author: Mr.Xu* @description: user实体类* @Date: 2021/11/2  20:08*/
@AllArgsConstructor
@NoArgsConstructor
@Data
public class User {private Integer uid;private String username;private String sex;private Date birthday;private String address;
}

实体类接口：

package com.Mr_Xu.dao;import com.Mr_Xu.bean.User;import java.util.List;/*** @Author: Mr.Xu* @description: 实体类接口* @Date: 2021/11/2  20:11*/
public interface UserDao {//查询所有用户信息，封装到list集合中List<User> findAll();int addUser(User user);int deleteUser(Integer uid);int Update(User user);//根据姓氏查询用户列表 方式一：张%  #{}List<User> getUserListByName1(String username);//根据姓氏查询用户列表 方式二：${value}List<User> getUserListByName2(String username);
}

实体类映射文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--mapper是dao接口映射文件的根标签namespace属性表示当前这个映射文件和哪一个dao接口对应namespace属性值就写对应的dao接口的全限定类名
-->
<mapper namespace="com.Mr_Xu.dao.UserDao"><!--select：查询id:对应dao接口中的方法名resultType：结果类型，对应dao接口方法的返回值类型情况1：如果方法的返回值是list泛型集合，就写list的泛型类型  需要注意：写泛型类型的时候也需要使用全限定类名--><select id="findAll" resultType="user">SELECT * FROM user</select><!--`#{}`可以有效防止 sql 注入`#{}`可以接收简单类型值或 pojo 属性值--><select id="getUserListByName1" resultType="user">SELECT * FROM user WHERE username LIKE CONCAT(#{username},'%')</select><!--`${}`不能防止 sql 注入`${}`可以接收单个简单类型值或 pojo 属性值--><select id="getUserListByName2" resultType="com.Mr_Xu.bean.User">select * from user where username like '${value}%'</select><delete id="addUser" parameterType="user">insert into user value (null,#{username},#{sex},#{birthday},#{address})</delete><delete id="deleteUser" parameterType="user">delete from user where uid = #{uid}</delete><update id="Update" parameterType="User">update user set username=#{username},sex=#{sex},address=#{address} where uid=#{uid}</update></mapper>

使用测试方法实现基本CRUD：

package com.Mr_Xu;import com.Mr_Xu.bean.User;
import com.Mr_Xu.dao.UserDao;import com.Mr_Xu.utils.MyBatisUtils;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;import java.io.InputStream;
import java.util.Date;
import java.util.List;/*** @Author: Mr.Xu* @description:* @Date: 2021/11/2  21:48*/
public class mybatisTest {//添加@Testpublic void f2() throws Exception {//获得mybatis核心类对象InputStream is = Resources.getResourceAsStream("mybatis-config.xml");//加载核心配置文件SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);//获得sqlSession对象SqlSession SqlSession = sqlSessionFactory.openSession();UserDao dao = SqlSession.getMapper(UserDao.class);User user = new User();user.setUsername("张三");user.setSex("男");user.setBirthday(new Date());user.setAddress("深圳");dao.addUser(user);SqlSession.commit();//释放资源SqlSession.close();}//删除@Testpublic void f3() throws Exception {//获取mybatis核心对象InputStream is = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);SqlSession sqlSession = sqlSessionFactory.openSession();UserDao dao = sqlSession.getMapper(UserDao.class);dao.deleteUser(10   );sqlSession.commit();sqlSession.close();}//修改@Testpublic void f4() throws Exception {InputStream is = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);SqlSession sqlSession = sqlSessionFactory.openSession();UserDao dao = sqlSession.getMapper(UserDao.class);User user = new User(8,"李四","女",new Date(),"北京");dao.Update(user);sqlSession.commit();sqlSession.close();}//查询@Testpublic void f1() throws Exception {//得到MyBatis的核心配置文件的文件流InputStream is = Resources.getResourceAsStream("mybatis-config.xml");//加载MyBatis的核心配置文件 获得SqlSessionFactory对象//使用了建造者模式和工厂模式，得到SqlSessionFactory 相当于连接池对象SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);//获得sqlSession对象 相当于Connection对象SqlSession sqlSession = sqlSessionFactory.openSession();//获得dao的代理对象  使用了代理模式UserDao dao = sqlSession.getMapper(UserDao.class);//调用方法操作List<User> list = dao.findAll();for (User user : list) {System.out.println("user = " + user);}//释放资源sqlSession.close();}//模糊查询,方式1:#{username},'%'@Testpublic void f5() throws Exception {//得到MyBatis的核心配置文件的文件流InputStream is = Resources.getResourceAsStream("mybatis-config.xml");//加载MyBatis的核心配置文件 获得SqlSessionFactory对象//使用了建造者模式和工厂模式，得到SqlSessionFactory 相当于连接池对象SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);//获得sqlSession对象 相当于Connection对象SqlSession sqlSession = sqlSessionFactory.openSession();//获得dao的代理对象  使用了代理模式UserDao dao = sqlSession.getMapper(UserDao.class);//调用方法操作List<User> list = dao.getUserListByName1("张");for (User user : list) {System.out.println("user = " + user);}//关闭流sqlSession.close();is.close();}//方式二：${value}%@Testpublic void f6() throws Exception {//获取核心文件流InputStream is = Resources.getResourceAsStream("mybatis-config.xml");//获取SqlSessionFactory对象SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);//获取SqlSession对象SqlSession sqlSession = sqlSessionFactory.openSession();//调用业务处理UserDao dao = sqlSession.getMapper(UserDao.class);//获取list集合List<User> list = dao.getUserListByName2("z");for (User user : list) {System.out.println("user = " + user);}//释放资源sqlSession.close();}
}

提取工具类：

package com.Mr_Xu.utils;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;
import java.io.InputStream;/*** @Author: Mr.Xu* @description:* @Date: 2021/11/3  8:58*/
public class MyBatisUtils {private static SqlSessionFactory sqlSessionFactory;static {try {//1.读取MyBatis核心配置文件InputStream is = Resources.getResourceAsStream("mybatis-config.xml");//2.加载MyBatis配置文件获取 SqlSessionFactory对象sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);} catch (IOException e) {e.printStackTrace();System.err.println("加载MyBatis核心配置文件失败！");}}/*** 获取SqlSession对象* @return SqlSession*/public static SqlSession getSqlSession(){return sqlSessionFactory.openSession();}/*** 释放资源* @param sqlSession*/public static void getClose(SqlSession sqlSession){if (sqlSession != null){sqlSession.close();}}
}

使用工具类实现：

 //使用工具类改造//增加@Testpublic void f10() throws Exception {//调用dao处理业务SqlSession sqlSession = MyBatisUtils.getSqlSession();UserDao dao = sqlSession.getMapper(UserDao.class);User user = new User(null,"张三","男",new Date(),"深圳");dao.addUser(user);//提交事务sqlSession.commit();//释放资源MyBatisUtils.getClose(sqlSession);}//删除@Testpublic void f11(){//获得SqlSession对象SqlSession sqlSession = MyBatisUtils.getSqlSession();//调用业务处理UserDao dao = sqlSession.getMapper(UserDao.class);dao.deleteUser(8);sqlSession.commit();//释放资源MyBatisUtils.getClose(sqlSession);}//修改@Testpublic void f12(){SqlSession sqlSession = MyBatisUtils.getSqlSession();UserDao dao = sqlSession.getMapper(UserDao.class);User user = new User(7, "李四", "女", new Date(), "北京");dao.Update(user);sqlSession.commit();MyBatisUtils.getClose(sqlSession);}//查看@Testpublic void f13(){SqlSession sqlSession = MyBatisUtils.getSqlSession();UserDao dao = sqlSession.getMapper(UserDao.class);List<User> list = dao.findAll();for (User user : list) {System.out.println("user = " + user);}sqlSession.commit();MyBatisUtils.getClose(sqlSession);}//模糊查询,方式一：#{username},'%'@Testpublic void f14(){SqlSession sqlSession = MyBatisUtils.getSqlSession();UserDao dao = sqlSession.getMapper(UserDao.class);List<User> list = dao.getUserListByName1("李");for (User user : list) {System.out.println("user = " + user);}sqlSession.commit();MyBatisUtils.getClose(sqlSession);}//方式二：${value}%@Testpublic void f15(){SqlSession sqlSession = MyBatisUtils.getSqlSession();UserDao dao = sqlSession.getMapper(UserDao.class);List<User> list = dao.getUserListByName2("l");for (User user : list) {System.out.println("user = " + user);}sqlSession.commit();MyBatisUtils.getClose(sqlSession);}