MyBatis工程搭建
项目总体结构图：
首先需要建一个数据库，SQL如下：
/*
Navicat MySQL Data Transfer
Source Server : 本地连接
Source Server Version : 80023
Source Host : localhost:3306
Source Database : mybatis_demo
Target Server Type : MYSQL
Target Server Version : 80023
File Encoding : 65001
Date: 2021-04-05 12:54:52
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int NOT NULL AUTO_INCREMENT,
`username` varchar(20) DEFAULT NULL,
`age` int DEFAULT NULL,
`score` int DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'peter', '18', '100');
INSERT INTO `user` VALUES ('2', 'pedro', '24', '200');
INSERT INTO `user` VALUES ('3', 'jerry', '28', '500');
INSERT INTO `user` VALUES ('4', 'mike', '12', '300');
INSERT INTO `user` VALUES ('5', 'tom', '27', '1000');
配置好pom.xml，配置文件如下：
<dependencies>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.23</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.6</version>
</dependency>
<!-- https://mvnrepository.com/artifact/ch.qos.logback/logback-classic -->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.3.0-alpha5</version>
<scope>test</scope>
</dependency>
</dependencies>
使用JDBC 连接及操作数据库,实现代码如下：
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class JDBCDemo {
public static void main(String[] args) throws Exception {
//1.注册驱动
Class.forName("com.mysql.cj.jdbc.Driver");
//2.获取连接
Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis_demo", "root", "ang76516");
//3.获取Statement对象
PreparedStatement preparedStatement = connection.prepareStatement("select * from user WHERE id = ?");
preparedStatement.setInt(1, 1);
//4.执行SQL语句返回结果集
ResultSet resultSet = preparedStatement.executeQuery();
//5.遍历结果集
while (resultSet.next()) {
System.out.println("username: " + resultSet.getString("username"));
System.out.println("age: " + resultSet.getString("age"));
}
//6.释放资源
resultSet.close();
preparedStatement.close();
connection.close();
}
}
运行结果：
总结：JDBC的缺点：代码多，效率不是太高！
使用通过引入MyBatis依赖
需要先配置一个核心文件，在resources下创建一个mybatis-config.xml文件，如下：
<?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>
<!-- 环境变量 -->
<environments default="development">
<environment id="development">
<!-- 事务管理器 -->
<transactionManager type="JDBC"/>
<!-- 数据源 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis_demo?useSSL=false"/>
<property name="username" value="root"/>
<property name="password" value="ang76516"/>
</dataSource>
</environment>
</environments>
<!-- mapper配置 -->
<mappers>
<mapper class="mapper.UserMapper"/>
</mappers>
</configuration>
StartWithXml.Java，代码实现如下：
import org.apache.ibatis.datasource.pooled.PooledDataSource;
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.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
import java.io.IOException;
import java.io.InputStream;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
@SuppressWarnings({"SqlResolve", "SqlNoDataSourceInspection", "Duplicates"})
public class StartWithXml {
public static void main(String[] args) throws SQLException, IOException {
InputStream configuration = Resources.getResourceAsStream("mybatis-config.xml");
/* // 准备jdbc事务类
JdbcTransactionFactory jdbcTransactionFactory = new JdbcTransactionFactory();
// 配置数据源
PooledDataSource dataSource = new PooledDataSource(
"com.mysql.cj.jdbc.Driver",
"jdbc:mysql://localhost:3306/mybatis_demo?useSSL=false",
"root",
"root");
// 配置环境，向环境中指定环境id、事务和数据源
Environment environment = new Environment.Builder("development")
.transactionFactory(jdbcTransactionFactory)
.dataSource(dataSource).build();
// 新建 MyBatis 配置类
Configuration configuration = new Configuration(environment);
*/
// 得到 SqlSessionFactory 核心类
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
// 开始一个 sql 会话
SqlSession session = sqlSessionFactory.openSession();
// 得到 sql 连接并运行 sql 语句
PreparedStatement preStatement = session
.getConnection()
.prepareStatement("SELECT * FROM user WHERE id = ?");
preStatement.setInt(1, 1);
ResultSet result = preStatement.executeQuery();
// 验证结果
while (result.next()) {
System.out.println("username: " + result.getString("username"));
System.out.println("age: " + result.getString("age"));
}
// 关闭会话
session.close();
}
}
运行结果如下：
MyBatis实现Mapper配置并查询数据
根据项目结构图，我们先编辑User类，代码如下：
public class User {
private Integer id;
private String username;
private String age;
private Integer score;
// getter&setter方法
public Integer getId(){
return id;
}
public void setId(Integer id){
this.id = id;
}
public String username(){
return username;
}
public void username(String username){
this.username = username;
}
public String age(){
return age;
}
public void setGenderName(String age){
this.age = age;
}
public Integer score(){
return score;
}
public void score(Integer score){
this.score=score;
}
// toString方法
public String toString(){
return "User{"+
"id="+id+
",name='"+username+'\''+
",genderName="+age+
",gender="+score+'}';
}
}
UserMapper接口类，代码如下：
import entity.User;
import org.apache.ibatis.annotations.Select;
public interface UserMapper {
/**
* 通过用户id查询用户名称
*
* @param id 用户id
* @return 用户名称
*/
@Select("SELECT username FROM user WHERE id = #{id}")
String selectUsernameById(Integer id);
/**
* 通过用户id查询用户年龄
*
* @param id 用户id
* @return 用户年龄
*/
Integer selectUserAgeById(Integer id);
/**
* 通过用户id查询用户信息
*
* @param id
* @return
*/
User selectUserById(Integer id);
}
还需要配置一个核心文件，之前已配好mybatis-config.xml，还需要配置UserMapper.xml，创建在resources下的mapper下没用的先创建，代码如下：
<?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 namespace="mapper.UserMapper">
<select id="selectUserAgeById" resultType="java.lang.Integer">SELECT age FROM user WHERE id = #{id}</select>
<select id="selectUserById" resultMap="userMap">SELECT * FROM user WHERE id = #{id}</select>
<resultMap id="userMap" type="entity.User">
<id property="id" column="id"/>
<result property="username" column="username"/>
<result property="age" column="age"/>
<result property="score" column="score"/>
</resultMap>
</mapper>
测试类UserTest.Java
import entity.User;
import mapper.UserMapper;
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 java.io.IOException;
import java.io.InputStream;
import java.sql.SQLException;
@SuppressWarnings({"Duplicates"})
public class UserTest {
public static void main(String[] args) throws IOException, SQLException {
// 读取配置文件
InputStream configuration = Resources.getResourceAsStream("mybatis-config.xml");
// 得到 SqlSessionFactory 核心类
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
// 开始一个 sql 会话
SqlSession session = sqlSessionFactory.openSession();
// 得到 mapper
UserMapper mapper = session.getMapper(UserMapper.class);
// 调用注解的SQL
String username = mapper.selectUsernameById(1);
System.out.println("username: " + username);
// 调用XML的SQL
Integer age = mapper.selectUserAgeById(1);
System.out.println("age: " + age);
// 调用通过用户id查询用户信息的方法
User user = mapper.selectUserById(1);
System.out.println(user);
// 关闭会话
session.close();
}
}
运行结果如下：
