Mybatis：入门

helloworld（入门）

建表语句

CREATE TABLE `tbl_employee`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `last_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `gender` char(1) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 2 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `tbl_employee` VALUES (1, 'tom', '0', 'tom@qq.com');

实体类：

@Data
@ToString
public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    private String gender;
}

pom.xml

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.1</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
        </dependency>

log4j.xml放在类路径下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

 <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
   <param name="Encoding" value="UTF-8" />
   <layout class="org.apache.log4j.PatternLayout">
    <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) 
" />
   </layout>
 </appender>
 <logger name="java.sql">
   <level value="debug" />
 </logger>
 <logger name="org.apache.ibatis">
   <level value="info" />
 </logger>
 <root>
   <level value="debug" />
   <appender-ref ref="STDOUT" />
 </root>
</log4j:configuration>

sql映射文件EmployeeMapper.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="com.wj.EmployeeMapper">
    <!--
    namespace:命名空间
    id:唯一标识
    resultType:返回值类型
    #{id}:从传递过来的参数中取出id值
    -->
    <select id="selectEmp" resultType="com.wj.bean.Employee">
        select
            id
            ,last_name as lastName
            ,email
            ,gender
        from
            tbl_employee
        where id = #{id}
    </select>
</mapper>

全局配置文件：

<?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>
    <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"/>
                <property name="username" value="root"/>
                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>
    <!--将我们写好的sql映射文件一定要注册在全局配置文件中-->
    <mappers>
        <mapper resource="EmployeeMapper.xml"/>
    </mappers>
</configuration>

编写测试类：

    @Test
    public void test() throws IOException {
        //1.根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //2.获取sqlSession实例，直接执行已经映射的sql语句
        SqlSession session = sqlSessionFactory.openSession();
        try {
            // sql的唯一标识 (namespace + id)    statement Unique identifier matching the statement to use.
            // 执行sql要用的参数 parameter A parameter object to pass to the statement.
            Employee employee = session.selectOne("com.wj.EmployeeMapper.selectEmp", 1);
            System.out.println(employee);
        } finally {
            session.close();
        }
    }

执行结果：

总结：

• 根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象（包含数据源相关信息）

• 编写sql映射文件，配置了每一个sql和sql的封装规则等

• 将SQL的映射文件注册在全局配置文件中

• 写代码

  • 根据全局配置文件获取SqlSessionFactory

  • 使用SqlSession工厂，获取sqlSession（一个sqlSession就是和数据库的一次会话，用完关闭）

  • 使用sql的唯一标识告诉Mybatis执行哪个sql。sql都是保存在Sql映射文件中的。

项目结构：

面向接口编程

官方文档中：

大意是说上一种方法是旧版本的写法，新版本中，可以使用接口的方式，使代码更加简介，可以避免类型转换等出错。

创建一个接口:EmployeeMapper.java

public interface EmployeeMapper {
    public Employee getEmpById(Integer id);
}

修改sql映射文件：

<?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="com.wj.dao.EmployeeMapper">
    <!--
    namespace:命名空间 接口的全类名
    id:唯一标识
    resultType:返回值类型
    #{id}:从传递过来的参数中取出id值
    -->
    <select id="getEmpById" resultType="com.wj.bean.Employee">
        select
            id
            ,last_name as lastName
            ,email
            ,gender
        from
            tbl_employee
        where id = #{id}
    </select>
</mapper>

测试：

    @Test
    public void test01() throws IOException {
        //1.根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession session = sqlSessionFactory.openSession();
        try {
            EmployeeMapper employeeMapper= session.getMapper(EmployeeMapper.class);
            Employee emp = employeeMapper.getEmpById(1);
            System.out.println(emp);
        } finally {
            session.close();
        }
    }

    private SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

执行结果：

此时，我们发现，并没有为EmployeeMapper编写实现类，竟然也执行了方法，打断点，发现用的是代理类实现