创建一个Mybatis工程

一、创建maven项目，导入相关jar包（配置pom.xml文件）

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.maolei</groupId>
  <artifactId>mybatis-study</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>pom</packaging>
  <modules>
      <module>mybatis-study-01</module>
  </modules>
  
  <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>
    </dependencies>
</project>

二、创建实体类和查询sql的接口

User.java

package com.maolei.pojo;

import lombok.Data;

//使用lombok
@Data
public class User {
    private int id;
    private String name;
    private String pwd;

}

UserMapper.java

package com.maolei.mapper;

import java.util.List;

import com.maolei.pojo.User;

public interface UserMapper {
    public List<User> getUser();

}

三、编写配置文件

1、数据库配置文件（db.properties）

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=GMT
username=root
password=123456

2、Mybatis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>
    <properties resource="db.properties"/>
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
        <!-- <setting name="mapUnderscoreToCamelCase" value="true"/> -->
        <!-- <setting name="logImpl" value="LOG4J"/> -->
    </settings>
    <typeAliases>
        <!-- <typeAlias alias="User" type="com.maolei.pojo.User"/> -->
        <package name="com.maolei.pojo"/>
    </typeAliases>
    <!--
    注释快捷键 ：ctrl+shift+/
    environments与environment值保持一致
    -->
    <environments default="mysql">
        <!--environment代表的是环境-->
        <environment id="mysql">
            <!--
                transactionManager：代表数据库的事务
                Type统一是JDBC
            -->
            <transactionManager type="JDBC"></transactionManager>
            <!--
                dataSource：代表数据源
                type：POOLED
             -->
            <dataSource type="POOLED">
                <!-- 配置数据库驱动 -->
                <property name="driver" value="${driver}"/>
                <!-- 配置url -->
                <property name="url" value="${url}"/>
                <!-- 配置用户名 -->
                <property name="username" value="${username}"/>
                <!-- 配置密码 -->
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!-- 
        <mapper resource="com/maolei/mapper/UserMapper.xml"/>
         -->
        <mapper class="com.maolei.mapper.UserMapper"/>
    </mappers>

</configuration>

3、接口映射文件（UserMapper.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.maolei.mapper.UserMapper">
    <select id="getUser" resultType="user">
        select * from user;
    </select>
</mapper>

这个UserMapper.xml文件要创建在resources下面的com.maolei.mapper包下面，这个包路径要与UserMapper.java的包路径相同！

如果UserMapper.xml与UserMapper.java放在同一包中，那就需要在pom.xml中添加静态资源过滤器

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
        </resource>
    </resources>
</build> 

四、编写测试类

MyTest.java

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

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 org.junit.Test;

import com.maolei.mapper.UserMapper;
import com.maolei.pojo.User;

public class MyTest {
    @Test
    public void getUser() throws IOException {
        //下面sqlsession的获取可以做成一个工具类
        String resource = "mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = ssf.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = userMapper.getUser();
        for (User user : userList) {
            System.out.println(user);
        }
    }

}

测试类执行结果：

User(id=1, name=王五, pwd=123456)
User(id=2, name=张三, pwd=123456)
User(id=3, name=李四, pwd=123456)
User(id=4, name=小明, pwd=123456)