Mybatis的入门案例

导入相关依赖

<?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.minifull</groupId>
    <artifactId>my_mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <!-- 导入依赖 -->
    <dependencies>
        <!-- mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <!-- 数据库驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.8</version>
            <scope>runtime</scope>
        </dependency>
        <!-- 日志 -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!-- JUnit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

创建数据库和表

-- 创建数据库
CREATE DATABASE IF NOT EXISTS db_mybatis CHARACTER SET utf8;
-- 创建数据表
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性别',
  `address` varchar(256) default NULL COMMENT '地址',
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- 添加记录
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (41,'老王','2018-02-27 17:47:08','男','北京'),(42,'小二王','2018-03-02 15:09:37','女','北京金燕龙'),(43,'小二王','2018-03-04 11:34:34','女','北京金燕龙'),(45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙'),(46,'老王','2018-03-07 17:37:26','男','北京'),(48,'小马宝莉','2018-03-08 11:44:00','女','北京修正');

创建实体类

@Data
public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
}

创建实体类的持久层接口

public interface UserMapper {
    /**
     * 查询所有用户
     *
     * @return
     */
    List<User> listAllUsers();
}

** 编写接口映射文件UserMapper.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.minifull.mapper.UserMapper">
    <!-- 配置查询所有用户 -->
    <select id="listAllUsers" resultType="com.minifull.pojo.User">
        SELECT * FROM user
    </select>
</mapper>

**编写Mybatis的主配置文件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>
    <!-- 全局变量 -->
    <properties>
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/db_mybatis"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
    </properties>

    <!--配置环境-->
    <environments default="development">
        <environment id="development">
            <!-- 配置事务类型 -->
            <transactionManager type="JDBC"></transactionManager>
            <!-- 配置数据源（连接池） -->
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <!-- 指定映射文件 -->
    <mappers>
        <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>

使用

public class MybatisTest {
    /**
     * Mybatis 入门案例
     */
    @Test
    public void testInit() {
        try {
            // 1. 读取配置文件
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            // 2. 创建 SqlSessionFactory 工厂
            SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
            SqlSessionFactory factory = builder.build(is);
            // 3. 从工厂获取 SqlSession 对象
            SqlSession sqlSession = factory.openSession();
            // 4. 使用 SqlSession 创建 dao接口的代理对象
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            // 5. 使用代理对象执行查询
            List<User> users = mapper.listAllUsers();
            users.forEach(System.out::println);
            // 6. 释放资源
            sqlSession.close();
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

注意事项

• mybatis的映射配置文件位置必须和dao接口的包结构相同
• 映射配置文件的 mapper 标签 namespace 属性的取值必须是 mapper 接口的全限定类名
• 映射配置文件的操作配置，id 属性的取值必须是 mapper 接口的方法名

做到以上几点，我们在开发中无需再写dao的实现类

解决org.apache.ibatis.binding.BindingException: Invalid bound statement (not found)问题
出现此异常时因为接口和映射的mapper文件不再同一目录下所致，maven工程在默认情况下src/main/java目录下的mapper文件是不发布到target目录下的，配置以下映射过滤

<build>      
    <resources>          
        <resource>               
            <directory>src/main/java</directory>               
            <includes>                   
                <include>**/*.xml</include>            
            </includes>
        </resource>
    </resources>
</build>