map.xml``文件的约束

<?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">

核心配置文件的约束

<?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">

第一步：创建maven工程并且在pro.xml中导入相关的依赖包

<dependencies>
           <!--导入mybatis依赖包-->
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis</artifactId>
             <version>3.5.2</version>
         </dependency>
            <!--导入junit测试依赖包-->
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
             <version>4.12</version>
             <scope>test</scope>
         </dependency>
      <!--导入mysql驱动依赖包-->
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
             <version>8.0.18</version>
         </dependency>
     </dependencies>

第二步：创建实体类，和接口

package com.zhu.dao;
import com.zhu.pojo.User;
import java.util.List;
public interface IUserDao {
    List<User> selectAllUser();
}
package com.zhu.pojo;
public class User {
    private int id;
    private String name;
    private String pwd;
    public User(){
    }
    public User(int id,String name,String pwd){
    }
    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;
    }
    public String getPwd() {
        return pwd;
    }
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

第三步：为接口配置对应的配置文件

<?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">
  <!--绑定一个对应的Dao或Mapper接口-->
<mapper namespace="com.zhu.dao.IUserDao">
     <!--id得对应相应的方法名，resultType对应返回类型的全限定名称-->
    <select id="selectAllUser" resultType="com.zhu.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

第四步：创建一个生成SqlSession对象的工具类

package com.zhu.utils;
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.IOException;
import java.io.InputStream;
public class MybatisUtils {
      private  static SqlSessionFactory sqlSessionFactory;
    static {
        try {
        //创建SqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession(){
    //通过SqlSessionFactory来创建SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

第五步：配置核心文件

1.配置连接数据库的相关信息
2.每一个接口相应的配置文件都得在核心配置文件中通过注册

<?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="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306"/>
                <property name="username" value="root"/>
                <property name="password" value="zhuminghua"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
    <!--注册相应接口的配置文件-->
        <mapper resource="com/zhu/dao/IUserDao.xml"/>
    </mappers>
</configuration>

没有在核心配置文件中注册相应接口的配置文件会报以下错误

watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTcyMzAwMw_size_16_color_FFFFFF_t_70_pic_center

由于maven的约定大于配置，我们可能遇到配置文件无法导出或者生效的问题。解决方案：在pom.xml文件中加入build配置

<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>