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建一个使用 MyBatis 连接数据库的项目涉及多个步骤。以下是一个简单的示例，展示如何创建一个 Maven 项目，配置 MyBatis，并编写相关的类、方法和测试用例

1.创建Maven项目

首先，创建一个 Maven 项目。你可以使用 IDE（如 IntelliJ IDEA 或 Eclipse）来创建项目，或者在命令行中使用以下命令：

mvn archetype:generate -DgroupId=com.example -DartifactId=mybatis-demo -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

2. 添加依赖 

在 pom.xml 文件中添加 MyBatis 和数据库驱动的依赖：

<dependencies><!-- MyBatis --><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.7</version></dependency><!-- MySQL 驱动 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.26</version></dependency><!-- 测试依赖 --><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version><scope>test</scope></dependency>
</dependencies>

3. 配置 MyBatis

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

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//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_demo"/><property name="username" value="root"/><property name="password" value="password"/></dataSource></environment></environments><mappers><mapper resource="com/example/mapper/UserMapper.xml"/></mappers>
</configuration>

 4. 创建实体类

创建一个简单的 User 实体类：

package com.example.model;public class User {private int id;private String name;private String email;// Getters and Setterspublic 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;}@Overridepublic String toString() {return "User{" +"id=" + id +", name='" + name + '\'' +", email='" + email + '\'' +'}';}
}

 5. 创建 Mapper 接口

创建一个 UserMapper 接口：

package com.example.mapper;import com.example.model.User;import java.util.List;public interface UserMapper {User selectUserById(int id);List<User> selectAllUsers();void insertUser(User user);void updateUser(User user);void deleteUser(int id);
}

 6. 创建 Mapper XML 文件

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

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mapper.UserMapper"><select id="selectUserById" resultType="com.example.model.User">SELECT * FROM users WHERE id = #{id}</select><select id="selectAllUsers" resultType="com.example.model.User">SELECT * FROM users</select><insert id="insertUser" parameterType="com.example.model.User">INSERT INTO users (name, email) VALUES (#{name}, #{email})</insert><update id="updateUser" parameterType="com.example.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>

7. 创建 MyBatis 工具类

创建一个工具类来获取 SqlSession：

package com.example.util;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;public class MyBatisUtil {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();}
}

 8. 编写测试用例

在 src/test/java 目录下创建一个测试类 UserMapperTest：

package com.example;import com.example.mapper.UserMapper;
import com.example.model.User;
import com.example.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;import java.util.List;public class UserMapperTest {@Testpublic void testSelectUserById() {try (SqlSession session = MyBatisUtil.getSqlSession()) {UserMapper mapper = session.getMapper(UserMapper.class);User user = mapper.selectUserById(1);System.out.println(user);}}@Testpublic void testSelectAllUsers() {try (SqlSession session = MyBatisUtil.getSqlSession()) {UserMapper mapper = session.getMapper(UserMapper.class);List<User> users = mapper.selectAllUsers();users.forEach(System.out::println);}}@Testpublic void testInsertUser() {try (SqlSession session = MyBatisUtil.getSqlSession()) {UserMapper mapper = session.getMapper(UserMapper.class);User user = new User();user.setName("John Doe");user.setEmail("[e-mail]");mapper.insertUser(user);session.commit();}}@Testpublic void testUpdateUser() {try (SqlSession session = MyBatisUtil.getSqlSession()) {UserMapper mapper = session.getMapper(UserMapper.class);User user = mapper.selectUserById(1);user.setName("Jane Doe");mapper.updateUser(user);session.commit();}}@Testpublic void testDeleteUser() {try (SqlSession session = MyBatisUtil.getSqlSession()) {UserMapper mapper = session.getMapper(UserMapper.class);mapper.deleteUser(1);session.commit();}}
}

 9. 运行测试

运行 UserMapperTest 类中的测试方法，确保 MyBatis 正确连接数据库并执行相应的操作。

10. 数据库表结构

确保数据库中有一个 users 表，表结构如下：

CREATE TABLE users (id INT AUTO_INCREMENT PRIMARY KEY,name VARCHAR(100) NOT NULL,email VARCHAR(100) NOT NULL
);

 总结：

以上步骤展示了如何创建一个使用 MyBatis 连接数据库的简单项目。你可以根据需要扩展这个项目，添加更多的功能和复杂性。