MyBits------怎样写出一个MyBatis

具体操作如下

准备工作 ：
新建一个普通的maven项目
删除src目录

• 1.准备一个数据库

CREATE DATABASE `mybatis`;
USE `mybatis`; 
CREATE TABLE `user`(   
   `id` INT(20) NOT NULL,    
   `name` VARCHAR(30) DEFAULT NULL,   
    `pwd` VARCHAR(30) DEFAULT NULL,    
     PRIMARY KEY(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8;

 INSERT INTO `user`(`id`,`name`,`pwd`) VALUES (1,'**','123456'),(2,'##','zxcvbn'),(3,'##','123456')

• 2.导入maven依赖

<dependencies>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.4</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.12</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/log4j/log4j -->
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/junit/junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>


</dependencies>

• 3.第一步配置在ReSource目录下 ==编写mybatis的核心配置文件 mybatis-config.xml ==，配置数据库连接,这段代码是固定的

<?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="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${pwd}"/>
            </dataSource>
        </environment>
    </environments>
    
  configuration>                                                                                                                                                                                             

• 4.编写一个mybatis工具类操作数据库（注意包不要导错）

package com.yang.utils;


import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.session.SqlSessionFactory;

import java.io.IOException;
import java.io.InputStream;

public class MyBatisUtils {
   private static SqlSessionFactory sqlSessionFactory;

   static {

       try {
           String resource = "mybatis-config.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
       } catch (IOException e) {
           e.printStackTrace();
       }
   }
   public static SqlSession getSession(){
     return sqlSessionFactory.openSession();
   }
}

• 5.配置了一个实体类，引入了Lombok

package com.yang.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;


@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int id;
    private String name;
    private String pwd;
}



**Lombok的依赖**

```java
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.12</version>
</dependency>

• 6.持久层mapper的操作接口

package com.yang.mapper;

import com.yang.pojo.User;

import java.util.List;

public interface UserMapper {

    List<User> getUserList();
    
}

• 7.在resource下创建与main目录对应的目录，创建UserMapper 对应的xml配置文件，并编写SQL语句
  注意点：

        1、namespace 绑定对应的接口，
        2、具体操作（CRUD）表情对应的id，为接口中的方法
  

<?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"> <!-- 原来我们都是编写具体的执行sql -->
<mapper namespace="com.yang.mapper.UserMapper">
    <select id="getUserList" resultType="User">
        select * from user;
     </select>             
 </mapper>

• 8.这个配置文件一定要注册到Mybatis的配置文件MyBatis-config.xml中

<mappers>
    <mapper resource="com/yang/mapper/RMapper.xml"/>
    <!--<mapper class="com.yang.mapper.UserMapper"/>-->
    <!--<package name="com.yang.mapper"/>-->
</mappers>
<!--
resource 资源对应的路径
class 接口对应的路径
-->

• 9.测试

import com.yang.mapper.UserMapper;
import com.yang.pojo.User;
import com.yang.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;

import java.util.List;

public class Test {
    public static void main(String[] args) {        // 如何获取接口

        SqlSession session = MyBatisUtils.getSession();
        UserMapper mapper = session.getMapper(UserMapper.class);


        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
       
}