Simple Edition

• Create a test table
• Create the corresponding JavaBean
• Create mybatis configuration file and sql mapping file
• test

MyBatis operation database

• Create MyBatis global profile

• Create SQL map file

• According to the global configuration file, use SqlSessionFactoryBuilder to create SqlSessionFactory.

String resource="mybatis-config.xml";
InputStream is = Resources.getResourceAsStream(resource);
SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(is);

• Get the SqlSession object using SqlSessionFactory. A SqlSession object represents a session with the database.

SqlSession sqlSession = sf.openSession();

Use SqlSession: query by Id

SqlSession sqlSession = sf.openSession();
try {
    Employee employee = sqlSession.selectOne("helloworld.EmployeeMapper.getEmployeeById", 1);
    System.out.println(employee);
} finally {
    sqlSession.close();
}

Full code

• Add related maven dependencies

<dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.19</version>
        <scope>runtime</scope>
    </dependency>

    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.2.7</version>
    </dependency>
</dependencies>

• Script database

create table t_employee(
      id int auto_increment,
      last_name varchar(255),
      email varchar(255),
      gender varchar(255),
      primary key(id)
);

insert into t_employee (last_name,email,gender)values('tom','tom@qq.com','male');

select * from t_employee;

• Write entity class

public class Employee {

    private Integer id;
    private String lastName;
    private String email;
    private String gender;

    // getter and setter

    // toString
}

• to write EmployeeMapper.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="helloworld.EmployeeMapper">
    <!--
    namespace: Namespace. Is the full class name of the interface.
    id: Unique identification.
    resultType: Return value type.
    #{id}: take the id value from the passed parameter

    public Employee getEmpById(Integer id);
     -->
    <select id="getEmployeeById" resultType="helloworld.Employee">
        select 
            id,
            last_name lastName,
            email,gender
        from t_employee
        where id = #{id}
    </select>
</mapper>

• Write the global configuration file MyBatis for 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>
    <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/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!-- To be written sql Mapping files( EmployeeMapper.xml)Be sure to register to the global profile( mybatis-config.xml)in -->
    <mappers>
        <mapper resource="helloworld/EmployeeMapper.xml"/>
    </mappers>
</configuration>

• Write main program

public class Test {
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        SqlSessionFactory sf = new SqlSessionFactoryBuilder().build(is);
       
        SqlSession sqlSession = sf.openSession();
        try {
            Employee employee = sqlSession.selectOne("helloworld.EmployeeMapper.getEmployeeById", 1);
            System.out.println(employee);
        } finally {
            sqlSession.close();
        }
    }
}

Interface programming

• Create a Dao interface

public interface EmployeeMapper {
    Employee getEmployeeById(Integer id);
}

• test

SqlSession sqlSession = sf.openSession();
try {
    // Using SqlSession to get mapper for operation
    EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
    Employee employee = mapper.getEmployeeById(1);
    System.out.println(employee);
} finally {
    sqlSession.close();
}

SqlSession

• The instance of SqlSession is non thread safe, so it cannot be shared.
• SqlSession needs to be closed properly after each use, which is necessary.
• SqlSession can directly call the id of the method for database operation.