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

绝地灬酷狼 2023-10-01 04:26 10阅读 0赞

### 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.version>3.4.2</mybatis.version>
        </properties>
        <dependencies>
    
            
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>${mybatis.version}</version>
            </dependency>
            
            <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>
    
    
        
        <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;
        }
    
        @Override
        public 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'}

可以看到，确实从数据库里取出了数据。

**这个整个项目的结构图**  
![struct][]

[struct]: https://img-blog.csdn.net/20180504165705580?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L25pdW5haTExMg==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70