mybatis快速入门

前面文章牵扯到数据库连接，所以也对mybatis做个总结，主要分为快速搭建，mybatis运行原理，springboot-mybatis结合运行核心，以及现在更方便的mybatis-plus几个系列

mybatis – MyBatis 3 | 简介

---

ORM框架

Object Relational Mapping为了解决面向对象与关系数据库存在的互不匹配的现象的技术

快速搭建

依赖

<dependencies>
  <!--mybatis依赖包-->
  <dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>${mybatis.version}</version>
  </dependency>

  <!--mysql链接驱动-->
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>${mysql-connector-java.version}</version>
  </dependency>

  <!--引入测试包-->
  <dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-api</artifactId>
    <version>${junit-jupiter-api.version}</version>
    <scope>test</scope>
  </dependency>
</dependencies>

mybatis配置类

<?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>
    <!--扫描POJO包,配合注解@Alias，后续给映射xml名字会比较短-->
    <typeAliases>
        <package name="com.daniel.entity"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/daniel_test?serverTimeZone=GMT+8;useSSL=false;characterEncoding=utf-8"/>
                <property name="username" value="root"/>
                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>
   <!--包扫描的方式将所有mapper添加进去-->
    <mappers>
        <package name="com.daniel.mapper"/>
    </mappers>
</configuration>

sqlSessionFactory的封装

public class MyBatisConfig {

    private static SqlSessionFactory sqlSessionFactory;

    static{
        try {
            InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            sqlSessionFactory =  new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public  static SqlSession getSqlSession(){
        SqlSession sqlSession = null;
        if(sqlSessionFactory!=null){
            sqlSession =  sqlSessionFactory.openSession();
        }
        return sqlSession;
    }

    public static  void closeSqlSession(){
        SqlSession sqlSession = getSqlSession();
        sqlSession.close();
    }

    public static <T> T getMapper(Class<T> type){
        SqlSession sqlSession = getSqlSession();
        return sqlSession.getMapper(type);
    }
}

StudentMapper.xml

这里IDEA可以安装mybatis的插件，可以帮我们生成这个xml，跳转也非常方便

<?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">
<!--这里namespace要对应我们的mapper接口的，也是通过这个和我们接口关联起来的-->
<mapper namespace="com.daniel.mapper.StudentMapper">

    <!--这是一个sql片段，方便公用-->
    <sql id="studentAllFiles">
        id,
        name,
        age,
        address,
        gender
    </sql>
    <select id="getAllStudent" resultType="Student">
        select <include refid="studentAllFiles"/> from student;
    </select>
</mapper>

Interface

public interface StudentMapper {
    List<Student> getAllStudent();
}

Entity

@Alias("Student")
public class Student {
    private Integer id;
    private int age;
    private String address;
    private String gender;
    private String name;

    public Integer getId() {
        return id;
    }

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

    public int getAge() {
        return age;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", age=" + age +
                ", address='" + address + '\'' +
                ", gender='" + gender + '\'' +
                ", name='" + name + '\'' +
                '}';
    }
}

编写测试类

public class MapperTest {

    @AfterEach
    public void close(){
        MyBatisConfig.closeSqlSession();
    }


    @Test
    public void testGetAllStudent(){
        List<Student> students = MyBatisConfig.getMapper(StudentMapper.class).getAllStudent();
        System.out.println(students);
    }

}

控制台输入： `[Student{id=1, age=20, address='陕西省西安市', gender='男', name='张三'}, Student{id=2, age=18, address='北京市', gender='女', name='Sisi'}]

OK,测试正常，mybatis就成功了。接下来总结下核心思想并debug下看下原理