【Mybatis学习笔记1】demo01-实现简单的select查询语句

一、什么是Mybatis

MyBatis 是一款优秀的持久层框架，它支持自定义SQL、存储过程以及高级映射。
MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。
MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

 

注：官网文档：https://mybatis.org/mybatis-3/zh/index.html

 

二、demo具体操作

1.本地mysql数据库，创建数据库mybatis，表user，字段分别是id(int)、name(varchar)、pwd(varchar)；

2.IDEA中创建一个module；

3.pom.xml文件中先后导入依赖：mysql-connector-java、mybatis、junit

    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.1</version>
        </dependency>
    </dependencies>

4.创建工具类MybatisUtils

package com.coke.utils;

import java.io.IOException;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;


public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

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

    }


    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

5.创建实体类User

package com.coke.pojo;

// 实体类

public class User {

    private int id;
    private String name;
    private String pwd;

    public User() {
    }

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

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

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

6.创建实体类对应的接口：查询全部用户接口

package com.coke.dao;

import com.coke.pojo.User;

import java.util.List;

public interface UserMapper {

    // 查询全部用户
    List<User> getUserList();


}

7.创建与接口对应的xml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">

<!-- namespace要和dao.Mapper的接口名一致 -->
<mapper namespace="com.coke.dao.UserMapper">
    <!--
        id 对应namespace中的方法名
        resultType sql执行的返回值
    -->
    <select id="getUserList"  resultType="com.coke.pojo.User">
        select * from mybatis.user
    </select>

</mapper>

8.配置jdbc参数

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;serverTimezone=Asia/Shanghai&amp;allowMultiQueries=TRUE" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>

    <!-- org.apache.ibatis.binding.BindingException: Type interface com.coke.dao.UserDao is not known to the MapperRegistry. -->

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

9.编写junit测试类

在test目录下创建与UserDao同级的测试类UserDaoTest

package com.coke.dao;

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

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class UserDaoTest {

    @Test
    public void test(){

        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList =  mapper.getUserList();

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

        sqlSession.commit();

    }

}

 

10.运行测试类，得到结果：

User{id=1, name='张三', pwd='123456'}
User{id=2, name='李四', pwd='111111'}
User{id=3, name='王五', pwd='666666'}

 

其中会有很多坑，下一篇会实现有where条件的查询、insert、update、delete。几行代码，几行配置，轻松实现！