2.Mybatis-搭建mybatis

1.创建maven工厂

引入如下依赖

 <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.33</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.17</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
    <!-- pom.xml -->
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
        <version>2.13.3</version>
    </dependency>

---

2.创建MyBatis的核心配置文件

进行配置

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!--  配置数据库环境  -->
    <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/test"/>
                <property name="username" value="root"/>
                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>
<!--  引入映射文件  -->
    <mappers>
        <mapper resource="mappers/UserMapper.xml"/>
    </mappers>
</configuration>

代码标签解释：

标签	核心属性	取值 / 说明
<environments>	default	指定默认环境的 id
<environment>	id	环境唯一标识（如 dev/test/prod），不可重复
<transactionManager>	type	JDBC（手动事务）/MANAGED（外部托管，如 Spring）
<dataSource>	type	POOLED（连接池，常用）/UNPOOLED（无连接池）/JNDI（容器数据源）

具体解释：

environments 配置连接多个数据库的环境

属性：1）default默认使用环境的id

2）environment配置某个具体的环境

属性：

1）id:配置数据库环境的唯一标识，不能重复

2）trasactionManager：设置事务管理方式

属性：

1）type：JDBC和MANAGED两个值

JDBC：事务的原生管理方式，需手动提交和回滚

MANAGED：被管理，例如spring

2）datasource：配置数据源

属性：type包括POOLED，UNPOOLED，JNDI

POOLED：使用数据库连接池缓存数据库连接

UNPOOLED：不使用数据库连接池

JNDI：表示使用上下文数据源

---

3.创建接口和映射文件

实体类

package com.demo.pojo;

public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private String sex;
    private String email;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
    public User(){

    }

    public User(Integer id, String username, String password, Integer age, String sex, String email) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
        this.sex = sex;
        this.email = email;
    }

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

接口

public interface UserMapper {

    /*
    * 面向接口编程两个一致
    * 1.namespace与类的全类名一致
    * 2.id与接口中的方法一致
    */
    int insertUser();
}

配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.demo.mapper.UserMapper">
    <insert id="insertUser">
        insert into t_user values(null,'张三','123455',11,'男','123@qq.com')
    </insert>
</mapper>

---

4.测试

    @Test
    public void test1() throws IOException {
        // 1.加载核心配置文件
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        // 2.创建SqlSessionFactoryBuilder
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        // 3.创建SqlSessionFactory
        SqlSessionFactory sessionFactory = sqlSessionFactoryBuilder.build(inputStream);
        // 4.获取SqlSession（openSession的true代表自动提交sql）
        SqlSession sqlSession = sessionFactory.openSession(true);
        // 5.创建mapper接口的代理对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int i = mapper.insertUser();
        //sqlSession.commit();
        System.out.println(i);

    }

---

5.加入日志功能

引入依赖

    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
        <version>2.13.3</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-api</artifactId>
    <version>2.13.3</version>
    </dependency>

配置log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration xmlns="http://logging.apache.org/log4j/2.0/config">

    <Appenders>
        <Console name="stdout" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
    </Appenders>

    <Loggers>
        <Logger name="org.apache.ibatis" level="debug"/>
        <Logger name="java.sql" level="debug"/>
        <Logger name="com.demo" level="debug"/>
        <Root level="info">
            <AppenderRef ref="stdout"/>
        </Root>
    </Loggers>

</Configuration>

---

6.查询测试

UserMapper定义方法

    User selectUser();

    List<User> selectAllUser();

映射文件

    <select id="selectUser" resultType="com.demo.pojo.User">
        select * from t_user where id=2
    </select>

    <select id="selectAllUser" resultType="com.demo.pojo.User">
        select * from t_user
    </select>

注：查询时必须要设置结果类型，有两种：

1）resultType为默认映射，字段名和属性名一致时用

2）resultMap为自定义映射，字段名和属性名不一致或多表查询字段名冲突时用

测试

    @Test
    public void test2() throws IOException {
        // 1.加载核心配置文件
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        // 2.创建SqlSessionFactoryBuilder
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        // 3.创建SqlSessionFactory
        SqlSessionFactory sessionFactory = sqlSessionFactoryBuilder.build(inputStream);
        // 4.获取SqlSession
        SqlSession sqlSession = sessionFactory.openSession(true);
        // 5.创建mapper接口的代理对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = mapper.selectAllUser();
        for (User user : users) {
            System.out.println(user);
        }

    }

---