使用mybatis框架完成数据库查询

配置pom配置文件

 首先在pom配置文件中添加mysql以及mybatis依赖,此处mysql依赖尽量与后续添加可视化数据库源所用的mysql驱动版本保持一致

<!--mybatis依赖-->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.6</version>
    </dependency>
    <!--mysql依赖-->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.29</version>
    </dependency>

之后添加资源文件指定

<build>
    <resources>
      <!--java目录-->
      <resource>
        <directory>src/main/java</directory>
        <includes>
          <include>**/*.xml</include>
          <include>**/*.properties</include>
        </includes>
      </resource>
      <!--resource目录-->
      <resource>
        <directory>src/main/resource</directory>
        <includes>
          <include>**/*.xml</include>
          <include>**/*.properties</include>
        </includes>
      </resource>
    </resources>
  </build>

添加jdbc.properties属性配置文件

在resource目录下添加jdbc属性配置文件

jdbc.driverClassName=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/qinsijun?userUnicode=true&character=utf-8
jdbc.username=root
jdbc.password=admin

创建查询实体类

实体类的属性需与所查询字段保持一致，如有自增字段构造方法须设置两个，全参构造方法和缺少自增字段属性的构造方法

package com.thugstyle.pojo;

public class Student {
    private Integer id;
    private String lojinName;
    private String lojinPwd;
    private String realName;

    public Student(Integer id, String lojinName, String lojinPwd, String realName) {
        this.id = id;
        this.lojinName = lojinName;
        this.lojinPwd = lojinPwd;
        this.realName = realName;
    }

    public Student(String lojinName, String lojinPwd, String realName) {
        this.lojinName = lojinName;
        this.lojinPwd = lojinPwd;
        this.realName = realName;
    }

    public Integer getId() {
        return id;
    }

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

    public String getLojinName() {
        return lojinName;
    }

    public void setLojinName(String lojinName) {
        this.lojinName = lojinName;
    }

    public String getLojinPwd() {
        return lojinPwd;
    }

    public void setLojinPwd(String lojinPwd) {
        this.lojinPwd = lojinPwd;
    }

    public String getRealName() {
        return realName;
    }

    public void setRealName(String realName) {
        this.realName = realName;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", lojinName='" + lojinName + '\'' +
                ", lojinPwd='" + lojinPwd + '\'' +
                ", realName='" + realName + '\'' +
                '}';
    }
}

配置StudentMapper.xml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是整个文件的大标签,用来开始和结束xml文件-->
<!--namespace指定命名空间,相当于包名,用来区分不同mapper.xml文件中相同的id属性-->
<mapper namespace="qsj">
<select id="getAll" resultType="com.thugstyle.pojo.Student">
/*resultType指定查询返回的结果类型,如果是集合,则必须是泛型类型
parameterType如果有参数,则必须通过他来指定参数的类型*/
    select id,lojinName,lojinPwd,realName from t_user
</select>
</mapper>

 配置 SqlMapConfig.xml核心配置文件

<?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">
<!--头部配置粘贴-->
<configuration>
       <!-- 第一步:读取jdbc属性配置文件-->
    <properties resource="jdbc.properties"></properties>
    <!--第二步:配置数据库环境变量,数据库连接配置-->
    <environments default="development">
        <!--开发时在公司使用的数据库配置-->
        <environment id="development">
            <!--id就是environments的default属性使用的-->
            <!--配置事务管理器,可通过查询mybatis源码包了解事务管理方式-->
           <!-- type:指定事务管理的方式
            JDBC:事务的控制交给程序员处理
            MANAGED:由容器(Spring)管理事务-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置数据源-->
           <!-- type:指定不同的配置方式
            JNDI:java命名目录接口,在服务器端进行数据库连接池的管理
            POOLED:使用数据库连接池
            UNPOOLED:不使用数据库连接池-->
            <dataSource type="POOLED">
                <!--配置数据库连接的基本参数-->
                <property name="driver" value="${jdbc.driverClassName}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--注册mapper.xml文件-->
    <mappers>
        <mapper resource="StudentMapper.xml"></mapper>
            <!--resource:通过resource目录下指定名称的文件注册
            url:使用绝对路径注册
            class:动态代理方式注册-->
    </mappers>
</configuration>

创建测试类完成查询

package com.thugstyle;

import com.thugstyle.pojo.Student;
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.Test;

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

public class MyTest {
    @Test
    public void TestMybatis() throws IOException {
       /* 使用文件流读取核心配置文件SqlMapConfig.xml*/
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        /*创建SqlSessionFactory工厂*/
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        /*取出SqlSession对象*/
        SqlSession sqlSession = factory.openSession();
        /*完成查询操作*/
        List<Student> list = sqlSession.selectList("qsj.getAll");
        list.forEach(student -> System.out.println(student));
        /*关闭sqlSession*/
        sqlSession.close();
    }
}