Java Mybatis快速入门之基本使用

目录

• 搭建环境
• 编写 Mybatis 核心配置文件
• pom导出资源失败
• 测试

搭建环境

新建Maven项目

导入Maven依赖

<dependencies>
    <!--mysql驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <!--Mybatis-->
    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    <!--junit-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

编写 Mybatis 核心配置文件

1.核心配置文件 mybatis-config.xml

注意, 在 xml 中 & 需要转义, 应该使用 &

<?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">

<!--核心配置文件-->
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

2.编写Mybatis工具类

package com.pro.utils;

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;

// SqlSessionFactory  --> SqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            // 获取 SqlSessionFactory 对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

3.编写接口

package com.pro.dao;

import com.pro.pojo.User;

import java.util.List;

public interface UserDao {
    public List<User> getUserList();
}

4.由原来的实现类转变为一个 Mapper 配置文件 UserMapper.xml

<?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">

<!--namespace: 绑定一个对应的 Dao/Mapper 接口-->
<mapper namespace="com.pro.dao.UserDao">

    <!--  id 绑定接口中方法  -->
    <select id="getUserList" resultType="com.pro.pojo.User">
        select * from user
    </select>
</mapper>

pom导出资源失败

<!--在pom.xml中配置build, 来防止我们资源导出失败问题-->
<build>
    <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>

测试

注意点

org.apache.ibatis.binding.BindingException: Type interface com.pro.dao.UserDao is not known to the MapperRegistry.

MapperRegistry

在核心配置文件中注册 mapper, 每一个 Mapper.xml 都需要在 Mybatis 核心配置文件中注册

<!--  每一个 Mapper.xml 都需要在 Mybatis 核心配置文件中注册  -->
<mappers>
    <mapper resource="com/pro/dao/UserMapper.xml"></mapper>
</mappers>

junit测试

package com.pro.dao;

import com.pro.pojo.User;
import com.pro.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {

    @Test
    public void test() {
        // 获取 sqlSession 对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        // 执行 SQL 方式一: getMapper
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }

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