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一、MyBatis简介

• mybatis是一个优秀的基于java的持久层框架，它内部封装了jdbc，使开发者只需要关注sql语句本身，而不需要花费精力去处理加载驱动、创建连接、创建statement等繁杂的过程。
• mybatis通过xml或注解的方式将要执行的各种statement配置起来，并通过java对象和statement中sql的动态参数进行映射生成最终执行的sql语句。
• 最后mybatis框架执行sql并将结果映射为java对象并返回。采用ORM思想解决了实体和数据库映射的问题，对jdbc进行了封装，屏蔽了jdbc api底层访问细节，使我们不用与jdbc api打交道，就可以完成对数据库的持久化操作。

二、快速入门案例

1. MyBatis开发步骤

1. 添加MyBatis的坐标

<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>MyBatis-Demo1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.32</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>


</project>

2. 创建user数据表

3. 编写User实体类

package com.jkj.domain;

public class User {
    private int id;
    private String username;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

4. 编写映射文件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="userMapper">
    <select id="findAll" resultType="com.jkj.domain.User">
        select * from user;
    </select>
</mapper>

5. 编写核心文件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 core file-->
       <configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatisthree?useSSL=false&useUnicode=true&characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!--加载sql映射文件-->
    <mappers>
        <mapper resource="com/jkj/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

6. 编写测试类

package com.jkj.test;

import com.jkj.domain.User;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MyBatisTest {
    @Test
    public void test() throws IOException {
        //1.加载MyBatis的核心配置文件获取sqlSessionFactory
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //2.获取sqlSession,执行sql
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //3.执行sql
        List<User> users = sqlSession.selectList("userMapper.findAll");
        System.out.println(users);
        //4.释放资源
        sqlSession.close();
    }
}

7.运行结果

2.MyBatis映射文件概述

1.映射文件DTD约束头

<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

2.根标签

<mapper > 
</mapper>

3.命名空间，与下面语句的id一起组成查询标识

namespace="userMapper"

4.查询操作，还有(insert,update,delete)

<select>
    
    </select>

5.语句的id标识，与上面的命名空间一起组成查询的标识

id="findAll"

6.查询结果对应的实体类

resultType="com.jkj.domain.User"

7.要执行的sql语句

select * from user;