MyBatis入门（一）基本CRUD操作_mybatis crud入门

什么是MyBatis

MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。 MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

具体使用

环境：idea2019，mysql8.0.25
准备工作：新建maven项目
项目目录结构：

1.在pom.xml文件中导入依赖

<dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.0.0.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <version>1.16.8</version>
      <scope>provided</scope>
    </dependency>
    <!--    连接数据库的驱动-->
    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.12</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-jdbc -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>5.0.0.RELEASE</version>
    </dependency>

    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.0.1</version>
      <scope>test</scope>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.6</version>
    </dependency>

    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>

<!--    控制台打印日志信息-->
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-to-slf4j</artifactId>
      <version>2.10.0</version>
    </dependency>

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>1.7.25</version>
    </dependency>
  </dependencies>
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2.实体类

数据库表如图：

package com.mb1.pojo;

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

@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class User01 {
    private int userId;
    private String username;
    private String password;
    private String email;

    public User01(String username, String password, String email) {
        this.username = username;
        this.password = password;
        this.email = email;
    }
}

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3.相关配置文件

位置在resources文件夹下。
数据库配置文件jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/book?spring&serverTimezone=GMT%2B8&useUnicode=true&characterEncodig=UTF-8&useSSL=false
jdbc.username=root
jdbc.password=123456
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log4j.properties文件，用于日志的打印

# Global logging configuration

log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
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用户映射文件UserMapper.xml

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mb1.map">
    <select id="selectAll"  resultType="com.mb1.pojo.User01">
        select * from user
    </select>
    <select id="selectOne"  resultType="com.mb1.pojo.User01" parameterType="int">
        select * from user where userId=#{userId};
    </select>

    <delete id="deleteById" parameterType="int">
        delete from user where userId=#{userId}
    </delete>

    <insert id="insertUser" parameterType="com.mb1.pojo.User01">
        insert into user(username,password,email) values(#{username},#{password},#{email})
    </insert>

    <update id="updateUser" parameterType="com.mb1.pojo.User01">
        update user set username=#{username} where userId=#{userId}
    </update>

</mapper>
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全局配置文件SqlMapperConfig.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>
<properties resource="jdbc.properties"></properties>
<!--    环境DEV,代码开发环境-->
    <environments default="dev">
        <environment id="dev">
<!--    Mybatis事务管理器-->
            <transactionManager type="JDBC"></transactionManager>
<!--    数据源POOLED用连接池,UNPOOLED,JNDI应用在EJB容器中-->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.username}" />
                <property name="password" value="${jdbc.password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="UserMapper.xml"></mapper>
    </mappers>
</configuration>
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4.测试类

package com.mb1.test;


import com.mb1.pojo.User01;
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;
import java.util.List;

public class TestM1 {
    public static void main(String[] args) throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapperConfig.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession session = sessionFactory.openSession(true);//自动提交事务，否则无法持久化到数据库
        ...//实现增删查改业务功能代码
    }

}

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4.1 添加

代码：

        User01 user = new User01("add","123","333333@qq.com");
        int count = session.insert("com.mb1.map.insertUser", user);
        System.out.println(count);
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运行截图：

4.2 删除

代码：

        int delete = session.delete("com.mb1.map.deleteById", 2);
        System.out.println(delete);
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运行截图：

4.3 查询

代码：

       //查找全部对象，只输出对象名
       List<User01> user01List = session.selectList("com.mb1.map.selectAll",User01.class);
       for(User01 u:user01List){
           System.out.println(u.getUsername());
       }
       //根据id查找单个对象
       User01 user01 = session.selectOne("com.mb1.map.selectOne", 4);
       System.out.println("查找单个对象"+user01);
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运行截图：

4.4 修改

代码：

       //根据用户id修改用户名
       User01 user01 = new User01();
       user01.setUserId(6);
       user01.setUsername("update");
       int update = session.update("com.mb1.map.updateUser", user01);
       System.out.println(update);
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运行截图：

其他

namespace即空间命名名称，用于区分实现数据持久化的方式。namespace一般绑定对应的文件的全路径。详解：namespace用法