第一个Mybatis程序

mybatis官方文档：https://mybatis.org/mybatis-3/zh/getting-started.html

思路：搭建环境 --> 导入Mybatis --> 编写代码 --> 测试

1.搭建数据库：

CREATE DATABASE `mybatistest`;

CREATE TABLE `user`(
	`id` INT(30) NOT NULL PRIMARY KEY,
	`name` VARCHAR(30) DEFAULT NULL,
	`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `mybatistest`.`user` (`id`, `name`, `pwd`) VALUES ('1', 'kaka', '123456'); 

INSERT INTO `mybatistest`.`user` (`id`, `name`, `pwd`) VALUES ('2', '卡卡发', '123456'); 

2.新建一个普通的maven项目：

删除src目录-->导入maven依赖

   <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

3.在项目中创建一个模块：

4.编写mybatis的核心配置文件

Resource文件夹：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">


<!--核心配置文件-->
<!--useSSL=true&amp;characterEncoding=UTF-8&amp;useUnicode=true&amp;serverTimezone=GMT-->
<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/mybatistest?useSSL=true&amp;useUnicode=true&amp;CharacterEncoding=UTF8&amp;serverTimezone=GMT"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

</configuration>

5.编写mybatis工具类

MybatisUtils：

package com.kakafa.util;

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 {

            //使用mybatis第一步:获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
    //SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

}

6.编写代码

实体类

package com.kakafa.pojo;

public class User {

    private int id;
    private String name;
    private String pwd;


    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = 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 + '\'' +
                '}';
    }
}

dao接口(UserDao接口，最好命名为UserMapper)

package com.kakafa.dao;

import com.kakafa.pojo.User;

import java.util.List;

public interface UserDao {
    List<User> getUserList();
}

接口实现类（UserMapper.xml）---> 即实现了原UserDaoImpl的功能

<?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">


<!--可以满足上个示例中 SqlSession 的调用-->

<!--namespace=绑定一个对应的dao接口（另一个比较常用的名称是Mapper接口）-->
<mapper namespace="com.kakafa.dao.UserDao">
    <!--select查询语句,id:对应的方法名字；resultType:返回类型-->
    <select id="getUserList" resultType="com.kakafa.pojo.User">
        select * from mybatistest.user
    </select>
</mapper>

7.测试

注意：

• 报错1：org.apache.ibatis.binding.BindingException: Type interface com.kakafa.dao.UserDao is not known to the MapperRegistry.

每一个Mapper.xml文件都需要在Mybatis核心配置文件中注册
mybatis-config.xml:

    <mappers>
        <mapper resource="com/kakafa/dao/UserMapper.xml"/>
    </mappers>

• 报错2：找不到Mapper.xml文件

pom.xml:

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

如果还是报错，则清除缓存，file->invalidate cache后再试试

junit:

package com.kakafa.dao;

import com.kakafa.pojo.User;
import com.kakafa.util.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {

    @Test
    public void test(){

        //1.获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //2.执行sql

        //方法一：getMapper
        UserDao mapper = sqlSession.getMapper(UserDao.class);//得到一个UserDao类型的对象
        List<User> userList = mapper.getUserList();

        for (User user : userList) {

            System.out.println(user);

        }
        //关闭sqlSession
        sqlSession.close();


    }
}

        //方法二：不推荐使用
        List<User> userList = sqlSession.selectList("com.kakafa.dao.UserDao.getUserList");