手撸MyBatis从配置文件到读出数据库的模拟实现
手动模拟MyBatis入门案例的底层实现：
需要了解的关键技术：
java反射、动态代理(comming soon）
一、Mybatis入门案例
点击此处跳过入门案例
首先看一下MyBatis最基础的入门案例
目标：读取数据库名为mybatis中的user表内容
maven依赖：
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.5</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.6</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.12</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
</dependency>
</dependencies>
Mybatis入门案例的两个配置文件：1.SqlMapConfig.xml 2.IUserDao.xml
1.SqlMapConfig.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="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<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="123"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="club/leyvan/dao/IUserDao.xml"/>
</mappers>
</configuration>
2.IUserDao.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="club.leyvan.dao.IUserDao">
<select id="findAll" resultType="club.leyvan.domain.User">
select * from user
</select>
</mapper>
实体类
package club.leyvan.domain;
import java.util.Date;
/**
* @Auther: http://www.leyvan.club
* @Date: 2019/12/13
* @Description: club.leyvan.domain
* @version: 1.0
*/
public class User {
/**
* `id` int(11) NOT NULL AUTO_INCREMENT,
* `username` varchar(32) NOT NULL COMMENT '用户名称',
* `birthday` date DEFAULT NULL COMMENT '生日',
* `sex` char(1) DEFAULT NULL COMMENT '性别',
* `address` varchar(256) DEFAULT NULL COMMENT '地址',
*/
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
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 Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
Dao层接口
package club.leyvan.dao;
import club.leyvan.domain.User;
import java.util.List;
/**
* @Auther: http://www.leyvan.club
* @Date: 2019/12/13
* @Description: club.leyvan.dao
* @version: 1.0
*/
public interface IUserDao {
public List<User> findAll();
}
测试类
package club.leyvan.test;
import club.leyvan.dao.IUserDao;
import club.leyvan.domain.User;
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.InputStream;
import java.util.List;
/**
* @Auther: http://www.leyvan.club
* @Date: 2019/12/13
* @Description: club.leyvan.test
* @version: 1.0
*/
public class Demo {
public static void main(String[] args) {
try{
//加载配置文件
InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
//构造者模式创建工厂建造者
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//工厂模式创建session
SqlSession session = factory.openSession();
//通过动态代理创建代理对象
IUserDao userDao = session.getMapper(IUserDao.class);
List<User> list = userDao.findAll();
for (User user: list) {
System.out.println(user);
}
session.close();
in.close();
}catch (Exception e){
e.printStackTrace();
}
}
}
输出结果：
User{id=1, username='王五', birthday=null, sex='2', address='null'}
User{id=10, username='张三', birthday=Thu Jul 10 00:00:00 CST 2014, sex='1', address='北京市'}
User{id=16, username='张小明', birthday=null, sex='1', address='河南郑州'}
User{id=22, username='陈小明', birthday=null, sex='1', address='河南郑州'}
User{id=24, username='张三丰', birthday=null, sex='1', address='河南郑州'}
User{id=25, username='陈小明', birthday=null, sex='1', address='河南郑州'}
User{id=26, username='王五', birthday=null, sex='null', address='null'}
二、模拟Mybatis实现上面的入门案例
将maven的依赖删除以后，手动模拟实现上面的入门案例：
[分析]
代码实现在GITHUB
结果：
使用的是XML
User{id=1, username='王五', birthday=null, sex='2', address='null'}
User{id=10, username='张三', birthday=2014-07-10, sex='1', address='北京市'}
User{id=16, username='张小明', birthday=null, sex='1', address='河南郑州'}
User{id=22, username='陈小明', birthday=null, sex='1', address='河南郑州'}
User{id=24, username='张三丰', birthday=null, sex='1', address='河南郑州'}
User{id=25, username='陈小明', birthday=null, sex='1', address='河南郑州'}
User{id=26, username='王五', birthday=null, sex='null', address='null'}
使用的是注解
User{id=1, username='王五', birthday=null, sex='2', address='null'}
User{id=10, username='张三', birthday=2014-07-10, sex='1', address='北京市'}
User{id=16, username='张小明', birthday=null, sex='1', address='河南郑州'}
User{id=22, username='陈小明', birthday=null, sex='1', address='河南郑州'}
User{id=24, username='张三丰', birthday=null, sex='1', address='河南郑州'}
User{id=25, username='陈小明', birthday=null, sex='1', address='河南郑州'}
User{id=26, username='王五', birthday=null, sex='null', address='null'}
