Mybatis的开发流程

1、引入依赖，Mybatis依赖和对应数据库的连接驱动

• 配置文件 pom.xml

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.4.6</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.46</version>
</dependency>

2、在Mybatis配置文件中配置数据库连接信息

• Mybatis配置文件 mybatis-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <!-- 开启驼峰命名转换 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
    <environments default="development">
        <environment id="development">
            <!-- 采用JDBC方式对数据库事务进行commit/rollback -->
            <transactionManager type="JDBC" />
            <!-- 配置数据库连接信息 -->
            <!-- 采用连接池方式管理数据库连接 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/数据库名" />
                <property name="username" value="root" />
                <property name="password" value="password" />
            </dataSource>
        </environment>
    </environments>
    <mappers>

    </mappers>
</configuration>

3、创建于数据表字段一致的实体类

• 实体类 Employee

public class Employee {
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private Date hiredate;
    private Float sal;
    private Float comm;
    private Integer deptno;
    //省略Getter和Setter方法
}

4、创建用于书写SQL语句的xml文件

• 映射器 emp.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="..mapper.EmpMapper">
    <select id="findById" parameterType="int"
            resultType="..entity.Employee">
        select * from emp where empno = #{value}
    </select>
</mapper>

• 到Mybatis配置文件中进行注册

<configuration>
    <mappers>
        <mapper resource="mapper/emp.xml"></mapper>
    </mappers>
</configuration>

5、启动程序

public static void main(String[] args) {
    // Mybatis的配置文件
    String resource = "mybatis-config.xml";
    // 利用Reader加载classpath下的Mybatis核心配置文件
    Reader reader = Resources.getResourceAsReader(resource);
    // 初始化SqlSessionFactory对象，同时解析Mybatis核心配置
    SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
    String statement = "..mapper.EmpMapper.findById";//与namespace及SQL语句的id对应
    // 创建SqlSession对象，SqlSession是JDBC的扩展类，用于与数据库交互
    SqlSession session = sessionFactory.openSession();
    Employee emp = session.selectOne(statement, 7566);
    System.out.println(emp.getName());
    // 如果transactionManager type="POOLED"，代表使用连接池，close是将连接回收到连接池中
    // 如果transactionManager type="UNPOOLED"，代表直连，close则会调用Connection.close()方法关闭连接
    session.close();
}