Mybaits 不写Dao的实现类 来实现Mybatis的查询（重点理解）

<?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>Mybatis_maven</groupId>
    <artifactId>day01_mbatis</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>

        <!--数据库 mysql 驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.45</version>
        </dependency>

        <!--junit 测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

<?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>

    <typeAliases>
        <package name=""/>
    </typeAliases>



    <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/test1"/>
                <property name="username" value="xxx"/>
                <property name="password" value="xxx"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <!-- 注意映射文件的路径与所对应的接口包路径一致， 或者干脆放在同一个包中-->
        <mapper resource="com/itheima/dao/IUserDao.xml"/>
    </mappers>
    
</configuration>

<?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">

<!--注意此处必须时接口的全限定类名 就是包名+类名 -->
<mapper namespace="com.itheima.dao.IUserDao">

    <!-- id的值必须时idao接口中的对应方法名   -->
    <select id="findAll" resultType="com.itheima.domain.User">
        select * from user
    </select>

</mapper>

package com.itheima.test;


import com.itheima.dao.IUserDao;
import com.itheima.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;

public class MybatisTest {

    public static void main(String[] args) throws Exception {

        InputStream in = Resources.getResourceAsStream("mybatis.xml");
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory s = builder.build(in);
        SqlSession sqlSession = s.openSession();

        //通过SqlSession创建Dao接口的代理对象
        IUserDao userdao = sqlSession.getMapper(IUserDao.class);

        List<User> users = userdao.findAll();
        for(User u :users){
            System.out.println(u);       结果：User{id=8, username=‘heheh‘, birthday=Sat Aug 24 00:00:00 CST 2019, sex=‘女‘, address=‘huana‘}
        } 
　　　　　　
        sqlSession.close();

    }
}