MyBatis HelloWorld

1. 环境搭建

1.1. pom.xml

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.6</version>
        <scope>provided</scope>
    </dependency>
    <!-- mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.1</version>
    </dependency>
    <!-- log4j 用于输出mybatis日志 -->
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
    <!-- mysql -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.32</version>
    </dependency>
</dependencies>

<build>
    <!-- resources标签 指定Maven构建项目时，要包含哪些资源文件
        1、默认情况下，Maven构建时只包含src/main/resources下的资源文件，其它目录，如src/main/java下的资源文件会被Maven忽略
        2、因为本项目Mapper配置文件放在src/main/java中，所以要指定包含这样资源文本
        3、设定了<resources>，那么默认的src/main/resources就会失效，所以src/main/resources还要额外指定
     -->
    <resources>
        <!-- 包含自定义位置的资源文件 -->
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.xml</include>
            </includes>
        </resource>
        <!-- 包含默认位置的资源文件 -->
        <resource>
            <directory>src/main/resources</directory>
        </resource>
    </resources>
</build>

1.2. 实体类

@Data
public class Person {
    private Long personId;
    private String name;
    private Date birthday;
}

1.3. Mapper

public interface PersonMapper {
    Person findById(Long personId);
    int deleteById(Long personId);
    int updateById(Person person);
    int insert(Person perosn);
}

1.4. SQL映射配置

<?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设置为对应Mapper的全类名 -->
<mapper namespace="demo.mybatis.mapper.PersonMapper">
    <select id="findById" resultType="demo.mybatis.entity.Person">
      SELECT * FROM person WHERE person_id = #{personId}
    </select>
    <delete id="deleteById">
      DELETE FROM person WHERE person_id = #{personId}
    </delete>
    <insert id="updateById">
      UPDATE person
      SET name = #{name}, birthday = #{birthday}
      WHERE person_id = #{personId}
    </insert>
    <insert id="insert">
      INSERT INTO person
      (name, birthday)
      VALUES
      (#{name}, #{birthday})
    </insert>
</mapper>

1.5. log4j配置文件

添加log4j.properties。Mybatis默认使用log4j输出日志信息，所以如果要将执行的SQL语句输出到控制台，需要在CLASSPATH（src目录）下添加log4j.properties，内容如下：

# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

1.6. MyBatis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>
    <settings>
        <!-- 支持属性使用驼峰的命名 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

    <!-- 和spring整合后 environments配置将废除 -->
    <environments default="development">
        <environment id="development">
            <!-- 使用jdbc事务管理 -->
            <transactionManager type="JDBC"/>
            <!-- 数据库连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url"
                          value="jdbc:mysql://localhost:3306/test?useSSL=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <!-- 声明SQL映射文件所在位置 -->
        <mapper resource="demo/mybatis/mapper/Person.xml"/>
    </mappers>
</configuration>

1.7. 测试方法

public class MabatisTest {
    SqlSessionFactory sqlSessionFactory = null;

    @Before
    public void setup() throws IOException {
        // 根据全局配置文件创建SqlSessionFactory，SqlSessionFactory负责创建SqlSession
        InputStream in = Resources.getResourceAsStream("sqlMapConfig.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
    }

    @Test
    public void findById() throws IOException {
        // 创建SqlSession。SqlSession代表与数据库之间的一次会话，底层就是封装了JDBC的Connection
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            // 获取Mapper，执行相应的操作
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            Person person = mapper.findById(1L);
            System.out.println(person);
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void insert() throws IOException {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            for (int i = 0; i < 10; i++) {
                Person person = new Person(null, "name" + i, new Date());
                int result = mapper.insert(person);
                System.out.println("result = " + result);
            }
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void deleteById() throws IOException {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            int result = mapper.deleteById(1L);
            System.out.println("result = " + result);
            // 增删改必须commit
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
    
    @Test
    public void updateById() throws IOException {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            Person person = new Person(5L, "Jack", new Date());
            mapper.updateById(person);
            sqlSession.commit();
        } finally {
            sqlSession.close();
        }
    }
}

2. 全局配置文件和SQL映射文件

全局配置文件：MyBatis的全局配置
SQL映射文件：Mapper接口的实现描述

3. 查看Mapper接口的实现类

查看Mapper接口的实现类，可以看到是动态代理

@Test
public void test() {
    SqlSession sqlSession = sqlSessionFactory.openSession();
    try {
        PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
        System.out.println(mapper.getClass());  // com.sun.proxy.$Proxy
    } finally {
        sqlSession.close();
    }
}