mybatis入门篇：通过SqlSession.selectList进行数据查询

作为一个java菜鸟，早就从慕课网中学到一些基本的mybatis的用法，但是一直不成体系，懵懵懂懂，既然正式入了java这个坑，就打算好好学学，所以买了本《MyBatis从入门到精通》，在此记录下学习的点滴。

数据库版本：Server version: 8.0.15 MySQL Community Server - GPL

数据准备：

先写一个最简单的查询

1、新建一个空白的maven项目，引入相关依赖包

    <dependencies>
        <!--测试需要-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version></version>
        </dependency>
        <!--数据库连接驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version></version>
        </dependency>
    </dependencies>

2、在resources中添加mybatis的配置文件mybatis-config.xml

这里选用最基本的jdbc事务管理器，不用数据库连接池。此处因为mysql的版本原因，要禁用SSL。同时配置数据库实体的位置和mapper文件路径。

<?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>
    <typeAliases>
        <package name="com.forest.owl.entity"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC">
                <property name="" value=""/>
            </transactionManager>
            <dataSource type="UNPOOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/forest?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

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

2、编辑数据库实体User

package com.forest.owl.entity;

import java.util.Date;

public class User {

    private int id;
    private String account;
    private String passwd;
    private String nickname;
    private String phone;
    private String email;
    private Date createTime;
    private Date updateTime;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getPasswd() {
        return passwd;
    }

    public void setPasswd(String passwd) {
        this.passwd = passwd;
    }

    public String getNickname() {
        return nickname;
    }

    public void setNickname(String nickname) {
        this.nickname = nickname;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }

    public Date getUpdateTime() {
        return updateTime;
    }

    public void setUpdateTime(Date updateTime) {
        this.updateTime = updateTime;
    }

}

3、在resources中添加mapper文件夹，在该文件夹中添加UserMapper.xml文件

mapper文件的命名空间是必须的，这里是随便命名，暂且还不清楚该属性的具体作用。

<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper">
    <select id="selectUsers" resultType="com.forest.owl.entity.User">
        SELECT id, account, passwd, nickname, phone, email, create_time as createTime, update_time as updateTime
        FROM user
    </select>
</mapper>

4、编写测试类

import com.forest.owl.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.BeforeClass;
import org.junit.Test;

import java.io.IOException;
import java.io.Reader;
import java.util.List;

public class TestUserMapper {

    private static SqlSessionFactory sqlSessionFactory;

    @BeforeClass
    public static void init(){
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void TestMybatis(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        List<User> userList = sqlSession.selectList("selectUsers");
        System.out.println(userList.size());
        System.out.println(userList.get(0).getNickname());
        System.out.println(userList.get(0).getCreateTime());
    }
}

测试结果：