数据准备

CREATE TABLE `user` (
	`id` int(11) NOT NULL,
	`username` varchar(30) NOT NULL,
	`sex` varchar(1) NOT NULL,
	`birthday` varchar(10) NOT NULL,
	`address` varchar(100) NOT NULL,
  	PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert into user values(1,"steven","1","1991-02-11","nanjing");
insert into user values(2,"sherry","0","1995-06-14","taizhou");
insert into user values(3,"steven007","1","1995-01-01","nanjing");
insert into user values(4,"sherry007","0","1995-12-31","taizhou");

搭建MyBatis工程

1.使用IDEA创建工程

2.引入项目使用的依赖

<dependencies>
	<dependency>
		<groupId>mysql</groupId>
		<artifactId>mysql-connector-java</artifactId>
		<version>5.1.41</version>
		<scope>runtime</scope>
	</dependency>
	<dependency>
		<groupId>org.mybatis</groupId>
		<artifactId>mybatis</artifactId>
		<version>3.2.2</version>
	</dependency>
</dependencies>

3.Mapper接口开发方式实现原理
Mapper接口开发方式只需要程序员编写Mapper接口即可，由Mybatis框架根据接口定义创建接口的动态代理对象。Mapper接口开发需要遵循以下规范:

• Mapper.xml文件中的namespace与Mapper接口的类路径相同。
• Mapper.xml中定义的statement的id与Mapper接口方法名相同 。
• Mapper.xml中定义的SQL的parameterType与Mapper接口方法的输入参数类型相同。
• Mapper.xml中定义的SQL的resultType与Mapper接口方法的输出参数类型相同。

4.编写MyBatis框架全局配置文件mybatis.xml
在项目目录“/src/main/resources”下新建config目录，并在config目录下新建mybatis.xml文件，具体代码如下。

<?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>
    <!-- 1.环境配置，和spring整合后environments配置将废除 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <!-- 配置数据源 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/study?useSSL=false" />
                <property name="username" value="root" />
                <property name="password" value="admin123" />
            </dataSource>
        </environment>
    </environments>

    <!-- 2.在全局配置文件中加载SQL映射文件 -->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

5.编写po类
在项目目录“/src/main/java/com/steven”下新建po(persistent object)目录，并在po目录下新建User类，具体代码如下。

public class User {
    //属性名要和数据库表的字段对应
    private Integer id;
    
    private String username;
    
    private String sex;
    
    private String birthday;
    
    private String address;

	public User() {
    }

	public User(Integer id, String username, String sex, String birthday, String address) {
        this.id = id;
        this.username = username;
        this.sex = sex;
        this.birthday = birthday;
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday='" + birthday + '\'' +
                ", address='" + address + '\'' +
                '}';
    }

    //get和set方法......
}

6.编写Mapper接口
在项目目录“/src/main/java/com/steven”下新建mapper目录，并在mapper目录下新建UserMapper接口，具体代码如下。

public interface UserMapper {
    User findUserById(Integer id);
}

7.编写SQL映射
在项目目录“/src/main/resources”下新建mapper目录，并在mapper目录下新建UserMapper.xml文件，具体代码如下。

<?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">
<!-- namespace的作用是对SQL进行分类管理，使用mapper代理方式开发，namespace的值是该文件的全限定名 -->
<mapper namespace="com.steven.mapper.UserMapper">
    <!-- 在映射文件中配置多个SQL语句 -->
    <!-- 
     id:标识映射文件中的SQL，对应Mapper接口类的方法名
     parameterType:指定输入参数的类型，对应Mapper接口类的方法入参类型
     resultType:指定SQL输出结果映射的Java对象类型
     #{}表示一个占位符，#{value}其中value表示接收输入参数的名称,如果输入参数是简单类型,那么#{}中的值可以任意。
     -->
    <!-- 根据用户id查找用户 -->
    <select id="findUserById" resultType="com.steven.po.User" parameterType="java.lang.Integer">
        select * from user
        where id=#{id}
    </select>
</mapper>

8.编写测试类
在项目目录“/src/test/java”下新建Test类，具体代码如下。

public class Test {
    public static void main(String[] args) throws Exception {
        //1.获取MyBatis全局配置文件流
        String resource = "config/mybatis.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //2.根据MyBatis配置信息创建会话工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //3.获取会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //4.获取Mapper
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //5.业务操作
        User user = userMapper.findUserById(1);
        System.out.println(user);
        sqlSession.close();
    }
}

User{id=1, username='steven', sex='1', birthday='1991-02-11', address='nanjing'}

9.工程目录