我的第一个mybatis入门

前言

---

一、mabatis是什么？

mybatis是一种持久层框架，用来跟数据库打交道的，主要体现在mvc分层开发中的dao层，mabatis框架可以实现java代码与sql代码的分离，并且封装了很多传统jdbc需要进行的传统的封装操作，节省了开发的时间，提高开发效率。

二、使用步骤

1.引入依赖（maven构建项目）

<?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\mybatisP1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>mybatis\mybatisP1 Maven Webapp</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>

        <!--导入mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <!--数据库jar包-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.18</version>
        </dependency>
        
    </dependencies>


    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>

            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>

        <finalName>mybatis\mybatisP1</finalName>
        <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
            <plugins>
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-war-plugin</artifactId>
                    <version>3.2.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

2.建表（account）

create table account
(
	id int not null
		primary key,
	username varchar(255) not null,
	money int(255) not null
);

3.实体类

package com.haihui.pojo;

public class User {
    
    
    private int id;
    private String username;
    private int money;

    public User() {
    
    
    }

    public User(int id, String username, int money) {
    
    
        this.id = id;
        this.username = username;
        this.money = money;
    }

    public User(String username, int money) {
    
    
        this.username = username;
        this.money = money;
    }

    public int getId() {
    
    
        return id;
    }

    public void setId(int id) {
    
    
        this.id = id;
    }
    
    public String getUsername() {
    
    
        return username;
    }

    public void setUsername(String username) {
    
    
        this.username = username;
    }

    public int getMoney() {
    
    
        return money;
    }

    public void setMoney(int money) {
    
    
        this.money = money;
    }

    @Override
    public String toString() {
    
    
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", money=" + money +
                '}';
    }
}

4.dao层

使用mapper，跟dao接口一个意思，只不过符合规范罢了

package com.haihui.dao;

import com.haihui.pojo.User;

import java.util.List;

public interface UserMapper {
    
    
    public List<User> queryAllUser();

    /*查询一个用户,根据id*/
    public User queryUserById(Integer id);

    /*添加一条数据*/
    public int addUser(User user);

    /*修改一条数据*/
    public int updateUser(User user);

    /*删除一条数据*/
    public int deleteUser(Integer id);

}

5.dao接口配置文件

<?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.haihui.dao.UserMapper">
    <!--resultType定义方法的返回类型，如果是集合类型，那么定义为集合里面的具体类型（范型）-->
    <select id="queryAllUser" resultType="user">
        select * from account
    </select>

    <select id="queryUserById" resultType="com.haihui.pojo.User">
        select * from account where id = #{id}
    </select>

    <!--在查询标签最好不要写注释-->
    <insert id="addUser"  parameterType="com.haihui.pojo.User" >
        insert into account(username,money) values(#{username},#{money})
    </insert>

    <update id="updateUser"  parameterType="com.haihui.pojo.User">
        update account set username=#{username},money=#{money} where id=#{id};
    </update>

    <delete id="deleteUser" parameterType="int">
        delete from account where id=#{id}
    </delete>

</mapper>

6.工具类

package com.haihui.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;

public class MybatisUtils {
    
    
    public static SqlSessionFactory sqlSessionFactory;

    static {
    
    
        //读取mybatis核心配置文件
        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
    
    
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
    
    
        //获取sqlSession对象
        return sqlSessionFactory.openSession();
    }
}

7.核心配置文件（resources下）

driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/sqlfiftypractice?useSSL=true&useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
username=root
password=123456

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>
    <!--引入外部配置文件-->
    <properties resource="db.properties">
        <!--额外的配置，跟外部配置文件具有一样的功能
        <property name="" value=""/>-->
    </properties>

    <typeAliases>
        <!--给全限定类名起一个别名，在映射文件中使用这个别名，节省了开发的时间-->
        <typeAlias type="com.haihui.pojo.User" alias="user"></typeAlias>

        <!--把整个包下的所有类都起一个别名，默认的别名类型首字母小写即可-->
        <package name="com.haihui.pojo"/>
     </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

    <!--每一个mapper.xml都需要在核心配置文件当中注册-->
    <mappers>
        <mapper resource="com/haihui/dao/UserMapper.xml"/>
    </mappers>


</configuration>

8.测试类

需要注意的是，在建立测试类的时候，应该和java项目结构具有相同的目录（java/com/lhh/dao）

package com.haihui.dao;

import com.haihui.pojo.User;
import com.haihui.util.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserTest {
    
    

    /*查询所有用户*/
    @Test
    public void test1(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = mapper.queryAllUser();

        for(User user:users){
    
    
            System.out.println(user);
        }

        //关闭资源
        sqlSession.close();
    }

    /*根据id进行查询*/
    @Test
    public void test2(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        User user = mapper.queryUserById(1);

        System.out.println(user);

        //关闭资源
        sqlSession.close();
    }
    
    /*添加用户*/
    @Test
    public void test3(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //int result = mapper.addUser(new User(5, "艾坤", 10000));
        int result2 = mapper.addUser(new User( "世界上", 2000));
        /*添加用户的时候一定要提交事务*/
        sqlSession.commit();

        System.out.println(result2+","+result2);

        //关闭资源
        sqlSession.close();
    }

    /*更新用户*/
    @Test
    public void test4(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int result = mapper.updateUser(new User(20, "tom", 400));

        /*添加用户的时候一定要提交事务*/
        sqlSession.commit();

        //关闭资源
        sqlSession.close();
    }

    /*删除用户*/
    @Test
    public void test5(){
    
    
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int i = mapper.deleteUser(3);
        System.out.println(i);

        /*添加用户的时候一定要提交事务*/
        sqlSession.commit();

        //关闭资源
        sqlSession.close();
    }
}

总结

mabstis，在进行测试的时候，主要是记住SqlSeesion对象，通过工具类获取对象即可。然后通过sqlSession的getMapper方法，就可以获取到mapper对象，调用相关的方法即可，实现增删改查的操作。