Mybatis源码分析之（一）搭建一个mybatis框架（写一个mybatis的Demo）

数据库工作：

首先准备工作，安装mysql，并且新建一张t_demo表

CREATE TABLE `t_demo` (`name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,`id` int(11) NOT NULL AUTO_INCREMENT,PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;INSERT INTO `t_demo` VALUES ('name1', 1);
INSERT INTO `t_demo` VALUES ('name2', 2);
INSERT INTO `t_demo` VALUES ('name3', 3);

JAVA工作：

下面就是java中的事情了。LZ用的maven来构建项目的

下面是pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.ahpu.wcj</groupId><artifactId>mybatisDemo</artifactId><version>1.0-SNAPSHOT</version><properties><!-- mybatis版本号 --><mybatis.version>3.4.2</mybatis.version></properties><dependencies><!--mybatis依赖 --><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>${mybatis.version}</version></dependency><!-- mysql驱动包 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.44</version></dependency></dependencies></project>

new SqlSessionFactoryBuilder().build();//这个使用mybatis的入口，其中要的参数是xml配置的输入流1

所以我们来配置一下mybatis的配置文件

mybatis.cfg.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><!-- 引入外部配置文件 --><properties resource="mysql.properties"></properties><environments default="default"><environment id="default"><transactionManager type="JDBC"></transactionManager><dataSource type="POOLED"><property name="driver" value="${jdbc.driver}"/><property name="url" value="${jdbc.url}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/></dataSource></environment></environments><mappers><mapper class="mapper.TDemoMapper"></mapper></mappers>
</configuration>

其中LZ引用了mysql.properties的资源，所以新建mysql.properties文件，是mysql的连接信息
mysql.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=utf8
jdbc.username=root
jdbc.password=root1234

接下来我们要新建entity和mapper
TDemo

package entity;public class TDemo {int id;String name;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "TDemo{" +"id=" + id +", name='" + name + '\'' +'}';}
}

TDemoMapper

package mapper;import entity.TDemo;import java.util.List;public interface TDemoMapper {List<TDemo> getAll();
}

最后新建mapper的映射文件

TDemoMapper.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="mapper.TDemoMapper"><resultMap id="baseMap" type="entity.TDemo"><result property="id" column="id" jdbcType="INTEGER"></result><result property="name" column="name" jdbcType="VARCHAR"></result></resultMap><select id="getAll" resultMap="baseMap">select * from t_demo</select>
</mapper>

到这个，mybatis配置文件就建好了。接下来我们就要来使用mybatis了
新建MybatisUtil，这个是用来解析xml，拿到sqlsession的类
MybatisUtil

package util;import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;public class MybatisUtil {public static SqlSession getSqlsession(){SqlSessionFactory build = new SqlSessionFactoryBuilder().build(MybatisUtil.class.getClassLoader().getResourceAsStream("mybatis.cfg.xml"));return build.openSession();}}

最后测试一下是否搭建成功
Test

package test;import entity.TDemo;
import mapper.TDemoMapper;
import org.apache.ibatis.session.SqlSession;
import util.MybatisUtil;import java.util.List;public class Test {public static void main(String[] args) {SqlSession sqlsession = MybatisUtil.getSqlsession();TDemoMapper mapper = sqlsession.getMapper(TDemoMapper.class);List<TDemo> all = mapper.getAll();for (TDemo item : all)System.out.println(item);}
}
运行结果如下
----------------------------------
TDemo{id=1, name='name1'}
TDemo{id=2, name='name2'}
TDemo{id=3, name='name3'}