MyBatis学习总结01

1 什么是mybatis?

• MyBatis 是一款优秀的持久层框架

• MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集的过程

• MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 实体类 【Plain Old Java Objects,普通的 Java对象】映射成数据库中的记录。

• Mybatis官方文档 : http://www.mybatis.org/mybatis-3/zh/index.html

2 mybatis的第一个程序

2.1 搭建环境

2.1.1 项目结构

2.1.2  pom文件添加依赖

 <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        <!--MySQL驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--日志-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!--实体类偷懒-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.10</version>
        </dependency>
    </dependencies>

<build>
        <!--引入配置文件-->
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

2.1.3 编写MyBatis核心配置文件 

2.1.3.1 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>

    <!--引入外部文件-->
    <properties resource="db.properties">
<!--        <property name="username" value="root"/>-->
    </properties>
    <settings>
        <!--标准日志工厂-->
        <!--        <setting name="logImpl" value="STDOUT_LOGGING"/>-->
        <setting name="logImpl" value="LOG4J"/>

    </settings>
    <!--实体类起别名-->
    <typeAliases>
        <package name="bean"/>
        <!--        <typeAlias type="com.bean.User" alias="User"></typeAlias>-->
    </typeAliases>
    <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="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 使用相对于类路径的资源引用 -->
    <mappers>
        <mapper resource="dao/UserMapper.xml"/>
    </mappers>
</configuration>

2.1.3.2  db.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&useSSL=true&useUnicode=true&characterEncoding=UTF-8
username=root
password=123456

2.1.3.3  log4j-properties

#将等级为DEBUG的日志信息输出到console和file这两个目的地，console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file

#控制台输出的相关设置
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%c]-%m%n

#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/log.log
log4j.appender.file.MaxFileSize=10mb
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n

#日志输出级别
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

2.1.4 编写MyBatis工具类 MyBatisUtils.java

package 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;

/**
 * @author MoooJL
 * @data 2020/9/22-20:42
 */
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 getSqlSession(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

2.2 编写代码

2.2.1 创建实体类

public class User {
   
   private int id;  //id
   private String name;   //姓名
   private String pwd;   //密码
   
   //构造,有参,无参
   //set/get
   //toString()
   
}

2.2.3 编写mapper接口类

public interface UserMapper {
   //查询全部用户
   List<User> selectUser();
   //根据id查询用户
   User selectUserById(int id);
    //添加一个用户
    int addUser(User user);
    //修改一个用户
    int updateUser(User user);
    //根据id删除用户
    int deleteUser(int id);
}

2.2.4 在UserMapper.xml文件插入相关SQL语句 附模糊查询格式

<?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="dao.UserMapper">
    <select id="selectUser" resultType="user">
    select * from mybatis.user
  </select>
    <select id="selectUserById" resultType="user" parameterType="int">
        select * from mybatis.user where id=#{id}
    </select>
    <insert id="addUser" parameterType="user">
        insert into mybatis.user (name,password) values(#{name},#{password})
    </insert>
    <update id="updateUser" parameterType="user">
        update mybatis.user set name=#{name} ,password=#{password} where id=#{id}
    </update>
    <delete id="deleteUser" parameterType="int">
        delete from mybatis.user where id=#{id}
    </delete>
</mapper>

<select id=”selectlike”>
    select * from user where bar like "%"#{value}"%"
</select>

2.2.5 编写测试代码

@Test
public void tsetSelectUserById() {
   SqlSession session = MybatisUtils.getSession();  //获取SqlSession连接
   UserMapper mapper = session.getMapper(UserMapper.class);
   User user = mapper.selectUserById(1);
   System.out.println(user);
   session.close();
}

@Test
public void testAddUser() {
   SqlSession session = MybatisUtils.getSession();
   UserMapper mapper = session.getMapper(UserMapper.class);
   User user = new User(5,"王五","zxcvbn");
   int i = mapper.addUser(user);
   System.out.println(i);
   session.commit(); //提交事务,重点!不写的话不会提交到数据库
   session.close();
}

@Test
public void testUpdateUser() {
   SqlSession session = MybatisUtils.getSession();
   UserMapper mapper = session.getMapper(UserMapper.class);
   User user = mapper.selectUserById(1);
   user.setPwd("asdfgh");
   int i = mapper.updateUser(user);
   System.out.println(i);
   session.commit(); //提交事务,重点!不写的话不会提交到数据库
   session.close();
}

@Test
public void testDeleteUser() {
   SqlSession session = MybatisUtils.getSession();
   UserMapper mapper = session.getMapper(UserMapper.class);
   int i = mapper.deleteUser(5);
   System.out.println(i);
   session.commit(); //提交事务,重点!不写的话不会提交到数据库
   session.close();
}

2.3 总结

• 所有的增删改操作都需要提交事务！

• 接口所有的普通参数，尽量都写上@Param参数，尤其是多个参数时，必须写上！

• 有时候根据业务的需求，可以考虑使用map传递参数！

• 为了规范操作，在SQL的配置文件中，我们尽量将Parameter参数和resultType都写上！