Mybatis的入门

1 Mybatis入门步骤

• 创建一张测试表。
• 创建对应的JavaBean。
• 创建Mybatis配置文件和SQL映射文件。
• 测试。

2 Mybatis-HelloWorld

• sql脚本：

DROP TABLE IF EXISTS `employee`;
CREATE TABLE `employee`  (
  `id` int(11) NOT NULL,
  `last_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `gender` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;
INSERT INTO `employee` VALUES (1, 'tom', '男', 'tom@qq.com');

• 导入Mybatis相关jar包的Maven坐标：

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.5</version>
</dependency>
<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.21</version>
</dependency>

• Employee.java

package com.sunxiaping.domain;

public class Employee {

    private Integer id;

    private String lastName;

    private String email;

    private String gender;

    public Integer getId() {
        return id;
    }

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

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

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

    public String getGender() {
        return gender;
    }

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

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
}

• 新建log4j.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
 
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
 
 <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
   <param name="Encoding" value="UTF-8" />
   <layout class="org.apache.log4j.PatternLayout">
    <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) \n" />
   </layout>
 </appender>
 <logger name="java.sql">
   <level value="debug" />
 </logger>
 <logger name="org.apache.ibatis">
   <level value="info" />
 </logger>
 <root>
   <level value="debug" />
   <appender-ref ref="STDOUT" />
 </root>
</log4j:configuration>

• 新建EmployeeMapper.java

package com.sunxiaping.mapper;

import com.sunxiaping.domain.Employee;

public interface EmployeeMapper {

    Employee findById(Integer id);

}

• 新建映射文件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="com.sunxiaping.mapper.EmployeeMapper">

    <select id="findById" resultType="com.sunxiaping.domain.Employee">
        SELECT id,last_name as lastName,email,gender
        FROM employee
        WHERE id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

• 新建全局配置文件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.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://192.168.134.100:3306/test?useUnicode=true&amp;characterEncoding=UTF-8&amp;autoReconnect=true&amp;useSSL=false&amp;serverTimezone=GMT%2B8&amp;allowPublicKeyRetrieval=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!-- 将写好的SQL映射文件注册到全局配置文件中 -->
        <mapper resource="com/sunxiaping/mapper/EmployeeMapper.xml"/>
    </mappers>
</configuration>

• 测试：

package com.sunxiaping;

import com.sunxiaping.domain.Employee;
import com.sunxiaping.mapper.EmployeeMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/**
 * ①接口式编程
 * ②SqlSession代表和数据库的一次会话，用完必须关闭。
 * ③SqlSession和Connection一样，都是线程不安全的。每次使用都应该去获取新的对象。
 * ④Mapper接口没有实现类，但是Mybatis会为这个接口生成一个代理对象。
 *      EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
 * ⑤两个重要的配置文件：
 *      Mybatis的全局配置文件：包含数据库连接池信息，事务管理器信息等系统运行环境
 *      Mybatis的SQL映射文件：保存每一个SQL语句的映射信息。
 *
 */
public class EmployeeTest {
    /**
     * ①根据XML配置文件（全局配置文件）创建一个SqlSessionFactory对象（有数据源等一些运行的环境信息）
     * ②sql映射文件：配置了每一个SQL，以及SQL的封装规则等。
     * ③将sql映射文件注册在全局配置文件中
     * ④写代码：
     *      - 根据全局配置文件获取SqlSessionFactory对象。
     *      - 使用SqlSessionFactory工厂，获取sqlSession对象，使用其来进行CRUD。
     *      - 一个sqlSession对象代表一次数据库的会话，用完关闭。
     *      - 使用sql的唯一标识来告诉Mybatis执行哪个SQL
     *
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
        Employee employee = employeeMapper.findById(1);
        System.out.println("employee = " + employee);

        sqlSession.close();
    }
}