使用 MyBatis 实现基本的 CRUD 操作

MyBatis 是一个优秀的持久层框架，它通过 XML 或注解将 SQL 查询、存储过程以及 Java 对象关联起来，简化了数据持久层的开发。本文将详细介绍如何使用 MyBatis 实现基本的 CRUD（Create、Read、Update、Delete）操作。

1. 环境准备

在开始之前，请确保已安装以下环境和工具：

• JDK 8 或更高版本
• Maven
• MySQL 数据库（或其他数据库）
• MyBatis 框架

1.1 创建数据库和表

首先，我们需要创建一个数据库和相应的表。在 MySQL 中执行以下 SQL 语句：

CREATE DATABASE mybatis_demo;

USE mybatis_demo;

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50),
    email VARCHAR(50)
);

1.2 创建 Maven 项目

创建一个新的 Maven 项目，并在 pom.xml 中添加以下依赖：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>mybatis-demo</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.9</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.23</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-spring</artifactId>
<version>2.0.6</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.3.5</version>
</dependency>
</dependencies>
</project>

2. 配置 MyBatis

2.1 MyBatis 配置文件

在 src/main/resources 目录下创建 mybatis-config.xml 配置文件：

<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>
</configuration>

2.2 MyBatis 映射文件

在 src/main/resources 目录下创建 UserMapper.xml 文件：

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mybatisdemo.mapper.UserMapper">
<resultMap id="UserResultMap" type="com.example.mybatisdemo.model.User">
<id property="id" column="id" />
<result property="name" column="name" />
<result property="email" column="email" />
</resultMap>
<select id="selectUser" resultMap="UserResultMap">
SELECT * FROM users WHERE id = #{id}
</select>
<insert id="insertUser" parameterType="com.example.mybatisdemo.model.User">
INSERT INTO users (name, email) VALUES (#{name}, #{email})
</insert>
<update id="updateUser" parameterType="com.example.mybatisdemo.model.User">
UPDATE users SET name = #{name}, email = #{email} WHERE id = #{id}
</update>
<delete id="deleteUser" parameterType="int">
DELETE FROM users WHERE id = #{id}
</delete>
</mapper>

3. 创建实体类和接口

3.1 创建 User 实体类

在 src/main/java/com/example/mybatisdemo/model 目录下创建 User.java 文件：

package com.example.mybatisdemo.model;
public class User {
private int id;
private String name;
private String email;
// Getters and Setters
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 getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
@Override
public String toString() {
return "User{id=" + id + ", name='" + name + '\'' + ", email='" + email + '\'' + '}';
}
}

3.2 创建 UserMapper 接口

在 src/main/java/com/example/mybatisdemo/mapper 目录下创建 UserMapper.java 文件：

package com.example.mybatisdemo.mapper;
import com.example.mybatisdemo.model.User;
import org.apache.ibatis.annotations.*;
@Mapper
public interface UserMapper {
@Select("SELECT * FROM users WHERE id = #{id}")
User selectUser(int id);
@Insert("INSERT INTO users(name, email) VALUES(#{name}, #{email})")
@Options(useGeneratedKeys = true, keyProperty = "id")
void insertUser(User user);
@Update("UPDATE users SET name=#{name}, email=#{email} WHERE id=#{id}")
void updateUser(User user);
@Delete("DELETE FROM users WHERE id=#{id}")
void deleteUser(int id);
}

4. 配置 Spring 和 MyBatis

4.1 Spring 配置文件

在 src/main/resources 目录下创建 applicationContext.xml 文件：

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="com.example.mybatisdemo"/>
<bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource">
<property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis_demo?useSSL=false&serverTimezone=UTC"/>
<property name="username" value="root"/>
<property name="password" value="password"/>
</bean>
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"/>
<property name="mapperLocations" value="classpath:com/example/mybatisdemo/mapper/*.xml"/>
</bean>
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.example.mybatisdemo.mapper"/>
</bean>
</beans>

5. 编写测试类

在 src/main/java/com/example/mybatisdemo 目录下创建 Main.java 文件：

package com.example.mybatisdemo;
import com.example.mybatisdemo.mapper.UserMapper;
import com.example.mybatisdemo.model.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
UserMapper userMapper = context.getBean(UserMapper.class);
// Create
User newUser = new User();
newUser.setName("John Doe");
newUser.setEmail("john.doe@example.com");
userMapper.insertUser(newUser);
System.out.println("Inserted: " + newUser);
// Read
User user = userMapper.selectUser(newUser.getId());
System.out.println("Selected: " + user);
// Update
user.setName("Jane Doe");
user.setEmail("jane.doe@example.com");
userMapper.updateUser(user);
System.out.println("Updated: " + user);
// Delete
userMapper.deleteUser(user.getId());
System.out.println("Deleted user with ID: " + user.getId());
}
}

6. 运行程序

确保 MySQL 数据库已启动，并在 applicationContext.xml 中正确配置数据库连接信息。然后运行 Main 类，你将看到 CRUD 操作的结果输出。