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MyBatis
,一款优秀的持久层框架,用于简化 JDBC 的操作。持久层
:负责将数据保存到数据库的代码。硬编码
操作繁琐
硬编码
:直接在代码中 注册驱动、获取连接;设置SQL语句;
操作繁琐
:需要 手动设置参数;手动封装结果集;
JDBC 示例:
public class Demo04 { public static void main(String[] args) throws ClassNotFoundException, SQLException { //加载驱动 Class.forName("com.mysql.jdbc.Driver"); //驱动管理器,输入URL,用户名,密码 Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/fruitdb?useSSL=false&useUnicode=true&CharacterEncoding=utf-8", "root", "Deng07112003"); String sql = "select * from t_fruit";//硬编码设置sql语句,查询全部 PreparedStatement pstm = connection.prepareStatement(sql); //执行查询,返回结果集 ResultSet rs = pstm.executeQuery(); List<Fruit> list = new ArrayList<>();//创建集合,利用泛型声明存放类型为Fruit对象 while(rs.next()){ //利用循环,遍历查询到的每一行信息 //将每一行中,每一列的信息都记录下来 //rs对象的get方法中,可以填充列的位置,也可以填充列名来指定 int fid = rs.getInt(1); String fname = rs.getString("fname"); int price = rs.getInt(3); int fcount = rs.getInt("fcount"); String remark = rs.getString(5); ///将每一行的信息都存放进Fruit对象 Fruit fruit = new Fruit(fid,fname,price,fcount,remark); list.add(fruit);//再用集合存放 } //关闭资源 rs.close(); pstm.close(); connection.close(); list.forEach(System.out::println); } }
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create database mybatis;
use mybatis;
drop table if exists tb_user;
create table tb_user(
id int primary key auto_increment,
username varchar(20),
password varchar(20),
gender char(1),
addr varchar(30)
);
insert into tb_user values(1, '张三', '123', '男', '北京');
insert into tb_user values(2, '李四', '456', '男', '上海');
insert into tb_user values(3, '王麻子', '789', '女', '广州');
<dependencies>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.6version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>8.0.28version>
dependency>
dependencies>
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?useSSL=false&useUnicode=true&CharacterEncoding=utf-8&serverTimezone=GMT%2B8"/>
<property name="username" value="root"/>
<property name="password" value="abc123"/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="UserMapper.xml"/>
mappers>
configuration>
package com.java.pojo;
/**
* @author .29.
* @create 2024-03-12 11:47
*/
public class User {
private int id;
private String username;
private String password;
private String gender;
private String addr;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getAddr() {
return addr;
}
public void setAddr(String addr) {
this.addr = addr;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
", gender='" + gender + '\'' +
", addr='" + addr + '\'' +
'}';
}
}
映射文件根据操作的数据命名,通常以Mapper结尾。
注意:映射文件需要在MyBatis核心配置文件中配置好才能被加载使用!
DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="test">
<select id="selectAll" resultType="com.java.pojo.User">
select * from tb_user;
select>
mapper>
/**
* @author .29.
* @create 2024-03-12 12:02
*/
public class mybatisDemo {
public static void main(String[] args) throws IOException {
//1. 加载mybatis配置文件,获取SqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//2. 获取SqlSession对象去执行SQL
SqlSession sqlSession = sqlSessionFactory.openSession();
//3. 执行SQL语句
//传入Mapper映射文件中SQL语句的 "命名空间+id"
List<User> users = sqlSession.selectList("test.selectAll");
System.out.println(users);
//释放资源
sqlSession.close();
}
}
测试输出结果
:
[User{id=1, username='张三', password='123', gender='男', addr='北京'}, User{id=2, username='李四', password='456', gender='男', addr='上海'}, User{id=3, username='王麻子', password='789', gender='女', addr='广州'}]
- 1
原因
:IDEA与数据库未建立连接,不识别表信息解决方式
:配置IDEA与MySQL数据库的连接👇👇
点击OK
即可完成连接!