MyBatis入门

MyBatis框架 - 它是一个优秀的持久层框架，用于在Java应用程序中与数据库进行交互。MyBatis主要的优势在于它可以将SQL语句和Java代码分离，使得代码结构更加清晰。开发人员可以在XML配置文件或者通过注解的方式编写SQL语句，MyBatis会根据这些SQL语句来操作数据库。例如，要查询数据库中的用户信息，在MyBatis中可以在XML文件中编写对应的SQL查询语句，然后通过MyBatis提供的接口方法在Java代码中调用这个SQL语句来获取用户信息。使用SSM框架可以提高开发效率，使得代码结构更加清晰，便于维护和扩展，在开发企业级Java Web应用时非常受欢迎。

操作实践

1.创建一个普通的Maven项目

项目结构

2.导入相关依赖

<?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_test01</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <!--MyBatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.9</version>
        </dependency>
        <!--MySQL连接-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>
        <!--测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <!--将项目中src/main/java目录下的XML等资源文件编译进classes文件夹-->
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
</project>

3.创建数据库

create database mybatis_test01;
use mybatis_test01;
create table users(
    uid int primary key auto_increment,
    uname varchar(20) not null ,
    uage int not null
);
insert into users(uname, uage) VALUES ('张三',18),('李四',18);

4.编写数据库连接的配置文件

mysql.driver=com.mysql.cj.jdbc.Driver
mysql.url=jdbc:mysql://localhost:3306/mybatis_test01?serverTimezone=UTC\
  &characterEncoding=utf-8&useUnicode=true&useSSL=false
mysql.username=root
mysql.password=123456

5.MyBatis核心配置文件

<?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>
    <!--加载类路径下的配置文件-->
    <properties resource="db.properties"/>
    <!--配置环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <!--数据库连接相关配置，db.properties文件中的内容-->
            <dataSource type="POOLED">
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

6.写一个POJO实体类

package com.treasure.pojo;


public class User {
	private int uid;
	private String uname;
	private int uage;

	public int getUid() {
		return uid;
	}

	public void setUid(int uid) {
		this.uid = uid;
	}

	public String getUname() {
		return uname;
	}

	public void setUname(String uname) {
		this.uname = uname;
	}

	public int getUage() {
		return uage;
	}

	public void setUage(int uage) {
		this.uage = uage;
	}
}

7.创建映射文件

<?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="com.treasure.pojo.User">
    <select id="findById" parameterType="int" resultType="com.treasure.pojo.User">
        select * from users where uid = #{id}
    </select>
</mapper>

8.在核心配置文件中注册Mapper

<mappers>
    <mapper resource="mapper/UserMapper.xml"/>
</mappers>

完整的核心配置文件代码如下：

<?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>
    <!--加载类路径下的配置文件-->
    <properties resource="db.properties"/>
    <!--配置环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <!--数据库连接相关配置，db.properties文件中的内容-->
            <dataSource type="POOLED">
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

9.编写测试类

package Test;

import com.treasure.pojo.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.Reader;

public class UserTest {
	@Test
	public void userFindById(){
		String res = "mybatis-config.xml";
		// 创建流
		Reader reader = null;

		try {
			// 读取mybatis-config.xml文件中的内容到reader
			reader = Resources.getResourceAsReader(res);
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
		// 初始化MyBatis数据库，创建SqlSessionFactory类的实例
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
		// 创建SqlSession实例
		SqlSession session = sqlSessionFactory.openSession();
		// 传入参数查询，返回结果
		User user = session.selectOne("findById",1);
		// 输出结果
		System.out.println(user.getUname());
		// 关闭session
		session.close();
	}
}