第一个Mybatis程序

• 思路：搭建环境—>导入Mybatis—>编写代码—>测试！

• 2.1、搭建环境

  2.1.1、搭建数据库

CREATE TABLE `Users`(
 `id` INT(10) NOT NULL,
 `name` VARCHAR(30) NOT NULL,
 `pwd` VARCHAR(30) NOT NULL,
 PRIMARY KEY(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `Users`(`id`,`name`,`pwd`) VALUES
(1,'王五','123456'),
(2,'张三','123423'),
(3,'李四','123456');

2.1.2、新建项目

• 新建了一个普通的 maven 项目
• 删除 src 目录
• 导入maven依赖

<!--导入依赖-->
<dependencies>
    <!--mysql驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.22</version>
    </dependency>
    <!--mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.3</version>
    </dependency>
    <!--junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>

2.2、创建一个模块

2.2.1、编写mybatis的核心配置文件

<?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-->
<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/shop?useUnicode=true&amp;characterEncoding=utf8&amp;useSSL=true&amp;serverTimezone=Asia/Shanghai"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

2.2.2、编写mybatis工具类

//sqlSessionFactory --> sqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try{
            //使用Mybatis第一步：获取aqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
    // 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();
    }
}

2.3、编写代码

2.3.1、实体类

public class User {
    private int id;
    private String name;
    private String pwd;
    public User() {
    }
    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public String getPwd() {
        return pwd;
    }
    public void setId(int id) {
        this.id = id;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}

2.3.2、Dao接口

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

2.3.3、接口实现类

由原来的UserDaoImpl转变为一个Mapper配置文件

<?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.saxon.dao.UseDao">
    
    <select id="getUserList" resultType="com.saxon.pojo.User">
        select * from users
    </select>
</mapper>

测试

注意一点：

org.apache.ibatis.binding.BindingException: Type interface com.chen.dao.UseDao is not known to the MapperRegistry.

<mappers>    <mapper resource="com/saxon/dao/UserMapper.xml"/></mappers>

public class UserDaoTest extends TestCase {
    @Test
    public void test(){
        //第一步：获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try {
            //执行sql
            //方式一：getMapper
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            List<User> userList = userDao.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        }finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }
}

2.4.1、junit测试

• 资源过滤问题 在pom.xml添加下面配置

<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>

可能会遇到的问题：

1. 配置文件没有注册
2. 绑定接口错误。
3. 方法名不对
4. 返回类型不对
5. Maven导出资源问题