Mybatis入门

1. 获取Mybatis

• github
  https://github.com/mybatis/mybatis-3/releases
• maven仓库
  https://mvnrepository.com/artifact/org.mybatis/mybatis

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.7</version>
</dependency>

• 中文文档
  https://mybatis.org/mybatis-3/zh/index.html

2. 第一个Mybatis程序

2.1 搭建数据库环境

CREATE DATABASE `mybatis`;

USE `mybatis`;

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

INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'zzq','123456'),
(2,'zzq22','123456'),
(3,'admin','123456');

2.2 新建项目

• 新建一个普通的maven项目
• 删除src目录
• 导入依赖
  pom.xml

<!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.26</version>
        </dependency>

        <!--Mybatis-->
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>

        <!--junit-->
        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
        </dependency>

    </dependencies>

• 创建一个模块
  • 编写Mybatis的核心配置文件mybatis-config.xml
resources目录下新建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-->
<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/mybatis?useUnicode=true&amp;characterEncoding=utf-8&amp;useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

• 编写Mybatis的工具类

package com.zzqsmile.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;

//sqlSessionFactory  ---> sqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            //使用Mybatis第一步 获取sqlSessionFactory
            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 sqlSessionFactory(){
        return sqlSessionFactory.openSession();
    }
}

2.3 编写代码

• 编写实体类

package com.zzqsmile.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

package com.zzqsmile.dao;

import com.zzqsmile.pojo.User;

import java.util.List;

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

• 接口实现类由原来的UserDaoimpl转变为Mapper配置文件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="org.mybatis.example.BlogMapper">
    <select id="getUserList" resultType="com.zzqsmile.pojo.User">
        select * from Blog where id = #{id}
    </select>
</mapper>

2.4测试

org.apache.ibatis.binding.BindingException: Type interface com.zzqsmile.dao.UserDao is not known to the MapperRegistry.
mybatis-config.xml:

<!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册-->

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

resource必须要是/