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MyBatis入门

news 2025/12/3 1:03:13

Mybatis执行流程如下：

步骤为：

读取MyBatis 配置文件mybatis-config.xml,加载数据源、事务等，管理映射文件
加载映射文件mapper.xml，用于映射表中列和实体属性的关系
定义SQL语句，在上一步的文件中加载。
创建会话工厂。(SqlSessionFactory)，数据库连接池
创建会话(SqlSession)，连接对象
通过Executor 操作数据库
输入参数和输出结果

下面我们用具体代码来了解Mybatis

1.导入mybatis的依赖,mysql驱动,junit

<dependencies><!--mybatis依赖--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.5</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.47</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version><scope>test</scope></dependency></dependencies>

2.在src/main/resources目录创建两类配置文件

局配置文件: mybatis-config.xml 对应的类:org.apache.ibatis.session.Configuration#Configuration()

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><!--环境配置:default:默认使用那个数据源--><environments default="mysql"><!--数据源环境--><environment id="mysql"><!--transactionManager:事务管理器JDBC:手动提交事务MANAGED:交给第三方框架管理--><transactionManager type="JDBC"/><!--数据源:type:数据源类型1. POOLED:带连接池的数据库,性能高2.JNDI:外部数据源3.UNPOOLED:不带连接池的数据源--><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver" /><property name="url" value="jdbc:mysql://localhost:3306/test" /><property name="username" value="root" /><property name="password" value="123456" /></dataSource></environment></environments><!--加载mapper映射文件-->
<!--    <mappers>-->
<!--        <mapper resource="org/mybatis/example/BlogMapper.xml"/>-->
<!--    </mappers>-->
</configuration>

mapper映射文件:一张表对应一个mapper映射文件

事务: 在同一个事务下,一组sql,要就全部成功,要就全部失败

事务四大特征:ACID

原子性
隔离性
持久性
一致性

3.为tb_user表创建对应的实体类User

package com.fs.entity;import java.util.Date;public class User {/*** 实体类属性的数据类型使用包装类*/private Integer id;private String username;private String password;private String sex;//日期类型:java.util.Dateprivate Date brithday;private String address;public Integer getId() {return id;}public void setId(Integer 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;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public Date getBrithday() {return brithday;}public void setBrithday(Date brithday) {this.brithday = brithday;}public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", sex='" + sex + '\'' +", brithday=" + brithday +", address='" + address + '\'' +'}';}public User() {}public User(Integer id, String username, String password, String sex, Date brithday, String address) {this.id = id;this.username = username;this.password = password;this.sex = sex;this.brithday = brithday;this.address = address;}public User(String username, String password, String sex, Date brithday, String address) {this.username = username;this.password = password;this.sex = sex;this.brithday = brithday;this.address = address;}
}

4.对应表mapper映射文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.mybatis.example.BlogMapper"></mapper>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace:命名空间,现在随便写后期专门写法
-->
<mapper namespace="xxx"><!--sql语句:每一个sql称为一个statement--><!--查询statement:select属性:id:唯一标识符parameterType:输入参数类型,如果输入参数简单数据类型,可以省略自定义类类型,一定不能省略:全限定名(包.类)resultType: 结果集类型:查询一条记录转换那个对象类型:自定义类类型,全限定名(包.类)sql语句占位符: #{名字},${名字}如果parameterType是简单数据类型,名字随便写如果parameterType是自定义类类型, 名字写的是类对应的属性名--><select id="queryById" parameterType="int" resultType="com.fs.entity.User">select * from tb_user where id=#{uid}</select></mapper>

package com.fs;import com.fs.entity.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;/*** 测试类*/
public class UserDaoTest {@Testpublic void testQueryById() throws IOException {//使用mybatis操作数据库/*1.加载mybatis全局配置文件2.创建SqlSessionFactory对象(构建者设计模式:SqlSessionFactoryBuilder)3.根据SqlSessionFactory对象创建sqlSession对象4.调用sqlSession对象的方法,执行sql语句5.关闭sqlSession*///1.加载mybatis全局配置文件InputStream in = Resources.getResourceAsStream(" mybatis-config.xml");//2.创建SqlSessionFactoryBuilder对象SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();//3.创建SqlSessionFactory对象SqlSessionFactory sqlSessionFactory = builder.build(in);//4.创建sqlSession对象SqlSession sqlSession = sqlSessionFactory.openSession();//5.执行sql语句 statementID:namespace.statementIdUser user=sqlSession.selectOne("xxx.queryById",1);System.out.println(user);//6.关闭sqlSessionsqlSession.close();}
}

可能会出现问题：