MyBatis介绍

MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Ordinary Java Object,普通的 Java对象)映射成数据库中的记录。

入门案例

搭建数据库

CREATE DATABASE `mybatis`;USE `mybatis`;CREATE TABLE `user`(`id` INT(20) NOT NULL PRIMARY KEY,`name` VARCHAR(30) DEFAULT NULL,`pwd`  VARCHAR(30) DEFAULT NULL)ENGINE=INNODB DEFAULT CHARSET=utf8;INSERT INTO `user`(`id`, `name`, `pwd`) VALUES
(1, 'TheShy', 'TS666'),
(2, 'Rookie', 'Rookie666'),
(3, 'ning', 'ning666')

使用 maven 新建项目，导入依赖

 <!--导入依赖--><dependencies><!--mysql驱动--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.26</version></dependency><!--mybatis--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.9</version></dependency><!--junit--><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency></dependencies>

编写 mybatis 核心配置文件，参考官网模板

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/><property name="username" value="root"/><property name="password" value="root"/></dataSource></environment></environments><!--每一个 Mapper.xml 都需要在 Mybatis 核心配置文件中注册--><mappers><mapper resource="com/zhouyue/dao/userMapper.xml"></mapper></mappers>
</configuration>

编写 mybatis 工具类

public class MyBatisUtils {private static SqlSessionFactory sqlSessionFactory;static{//使用 MyBatis 第一步，获取 SqlSessionFactory 对象String resource = "mybatis-config.xml";InputStream inputStream = null;try {inputStream = Resources.getResourceAsStream(resource);} catch (IOException e) {e.printStackTrace();}sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);}//SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。// 你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句public static SqlSession getSqlSession(){return sqlSessionFactory.openSession();}

编写代码

实体类

//实体类
public class User {private int id;private String name;private String pwd;public User() {}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPwd() {return pwd;}public void setPwd(String pwd) {this.pwd = pwd;}public User(int id, String name, String pwd) {this.id = id;this.name = name;this.pwd = pwd;}@Overridepublic String toString() {return "User{" +"id=" + id +", name='" + name + '\'' +", pwd='" + pwd + '\'' +'}';}
}

Dao 接口

public interface UserDao {List<User> getUserList();
}

接口实现类，使用配置文件形式，注意要在 mybatis 核心配置文件里面配置一下

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace 用来绑定一个对应的 Dao/Mapper 接口-->
<mapper namespace="com.zhouyue.dao.UserDao"><!--select 查询语句，这里 id 设置为接口中对应的方法--><!--resultType 为返回值类型，要写全路径--><select id="getUserList" resultType="com.zhouyue.pojo.User">select * from mybatis.user</select>
</mapper>

由于我们要在非 resources 文件夹下面创建了 xml 文件，因此需要在 maven 的 pom.xml 中配置如下信息

<!--在 build 中配置 resources, 来防止我们资源导出失败问题--><build><resources><resource><directory>src/main/resources</directory><includes><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>true</filtering></resource><resource><directory>src/main/java</directory><includes><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>true</filtering></resource></resources></build>

测试

@Testpublic void test(){//获得 SqlSession 对象SqlSession sqlSession = MyBatisUtils.getSqlSession();//执行 sqlUserDao mapper = sqlSession.getMapper(UserDao.class);List<User> userList = mapper.getUserList();for (User user : userList) {System.out.println(user);}//关闭 SqlSession 对象sqlSession.close();}