mybatis知识点总结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！