(一)

用一个 Java Maven 项目说明 MyBatis 的基本使用

开始之前已准备好数据库和相关数据用户演示, 这里已创建好ryan数据库, student表, 表数据如下:

 

新建Maven项目 mybatis01:

一. 导入 mybatis: (以及mybatis依赖的mysql包)

<?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>com.ryan</groupId>
    <artifactId>mybatis01</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.21</version>
        </dependency>
    </dependencies>

</project>

二. 在resources目录下创建mybatis的配置文件 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>
    <!--配置MyBatis运行环境-->
    <environments default="development">
        <environment id="development">
            <!--配置JDBC的事务管理-->
            <transactionManager type="JDBC"></transactionManager>
            <!--POOLED配置JDBC数据源连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<!--                如下, 如果不指定编码, 可能会报空指针异常-->
<!--                <property name="url" value="jdbc:mysql://localhost:3306/ryan?serverTimezone=GMT%2B8"/>-->
                <property name="url" value="jdbc:mysql://localhost:3306/ryan?serverTimezone=GMT%2B8&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="613025"/>
            </dataSource>
        </environment>
    </environments>

    <!--注册userMapper.xml-->
    <mappers>
        <mapper resource="com/ryan/mapper/userMapper.xml"></mapper>
    </mappers>
</configuration>

三. 在新建的包下创建mapper配置文件, (每一个Java类都有一个对应的mapper, 在此配置文件中写sql):

<?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的值为mapper配置文件的路径, 不用写后缀-->
<mapper namespace="com.ryan.mapper.userMapper">
    <!--parameterType的值为对应的Java类, 之后将通过id调用对应sql-->
    <insert id="save" parameterType="com.ryan.javaClass.User">

    </insert>
</mapper>

四. 将mapper配置文件加载到mybais的配置文件 mybatis-config.xml 中:

    ...
        </environment>
    </environments>

    <!--注册userMapper.xml-->
    <mappers>
        <mapper resource="com/ryan/mapper/userMapper.xml"></mapper> </mappers> </configuration>

五. 创建User类, 其属性名和类型需与数据表中的字段相对应:

package com.ryan.javaClass;

public class User {

        private int id;
        private String name;
        private int phoneNumber;

        public User(int id, String name, int phoneNumber) {
            this.id = id;
            this.name = name;
            this.phoneNumber = phoneNumber;
        }
}

六. 创建Test类, 在这里操作数据库数据:

public class Test {

    public static void main(String[] args) {
        //加载MyBatis配置文件
        InputStream inputStream = Test.class.getClassLoader().getResourceAsStream("mybatis-config.xml");
        //需要先获取SqlSessionFactoryBuilder, 通过其获取SqlSessionFactory, 再通过其获取SqlSession, 最后用SqlSession操作数据
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        String statement = "com.ryan.mapper.userMapper.save";

        User user = new User(5488, "嬴政", 668688);
        sqlSession.insert(statement, user);
        sqlSession.commit();
    }
}

七. 编写sql:

<!--namespace的值为mapper配置文件的路径, 不用写后缀-->
<mapper namespace="com.ryan.mapper.userMapper">
    <!--parameterType的值为对应的Java类, 之后将通过id调用对应sql-->
    <insert id="save" parameterType="com.ryan.javaClass.User">
        insert into student(id,name,phoneNumber)values(#{id},#{name},#{phoneNumber})
    </insert>

    <insert id="search" parameterType="com.ryan.javaClass.User">
        select * from student where id = 5877
    </insert>
</mapper>

八. 运行Test.main():

在运行前, 还需进行一些步骤, IDEA默认只能读取resources目录下的配置文件, 上面的mapper文件是在java目录下的, 所以对此我们需要进行一些配置让IDEA能读取到此配置文件, 方法是在pom中添加如下配置:

    ...
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.21</version>
        </dependency>
    </dependencies>

    <!--IDEA默认只能读取resource目录下的配置文件, 此配置设置IDEA能读取设定目录下的所有配置文件-->
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
            </resource>
        </resources>
    </build>

</project>

运行后刷新数据库: