MyBatis簡介

MyBatis是Apache的一個開源項目，前身是iBatis。它是一個基于Java的持久層框架，主要特點包括：相比Hibernate等ORM框架，MyBatis更加輕量級，并且支持自定義SQL，能夠充分利用數據庫特性。

環境搭建

Maven依賴

首先在pom.xml中添加MyBatis相關依賴：

<dependencies><!-- MyBatis核心依賴 --><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.13</version></dependency><!-- MySQL驅動 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version></dependency>
</dependencies>

數據庫表結構

創建一個用戶表：

CREATE TABLE `user` (`id` int(11) NOT NULL AUTO_INCREMENT,`username` varchar(50) NOT NULL,`email` varchar(100) DEFAULT NULL,`age` int(3) DEFAULT NULL,`created_time` datetime DEFAULT CURRENT_TIMESTAMP,PRIMARY KEY (`id`)
);

核心配置

MyBatis配置文件

創建mybatis-config.xml核心配置文件：

<?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><!-- 屬性配置 --><properties resource="database.properties"/><!-- 設置 --><settings><!-- 開啟駝峰命名自動映射 --><setting name="mapUnderscoreToCamelCase" value="true"/></settings><!-- 類型別名 --><typeAliases><package name="com.example.entity"/></typeAliases><!-- 環境配置 --><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${database.driver}"/><property name="url" value="${database.url}"/><property name="username" value="${database.username}"/><property name="password" value="${database.password}"/></dataSource></environment></environments><!-- 映射器配置 --><mappers><mapper resource="mapper/UserMapper.xml"/></mappers>
</configuration>

數據庫配置文件

創建database.properties文件：

database.driver=com.mysql.cj.jdbc.Driver
database.url=jdbc:mysql://localhost:3306/mybatis
database.username=root
database.password=123456

實體類

創建User實體類：

package com.example.entity;import java.time.LocalDateTime;public class User {private Integer id;private String username;private String email;private Integer age;private LocalDateTime createdTime;// 構造方法public User() {}public User(String username, String email, Integer age) {this.username = username;this.email = email;this.age = age;}// getter和setter方法public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public LocalDateTime getCreatedTime() {return createdTime;}public void setCreatedTime(LocalDateTime createdTime) {this.createdTime = createdTime;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", email='" + email + '\'' +", age=" + age +", createdTime=" + createdTime +'}';}
}

基礎CRUD操作

Mapper接口

創建UserMapper接口：

package com.example.mapper;import com.example.entity.User;
import java.util.List;public interface UserMapper {// 插入用戶int insertUser(User user);// 根據ID刪除用戶int deleteUserById(Integer id);// 更新用戶信息int updateUser(User user);// 根據ID查詢用戶User selectUserById(Integer id);// 查詢所有用戶List<User> selectAllUsers();// 根據用戶名查詢用戶List<User> selectUsersByUsername(String username);
}

Mapper XML映射文件

創建UserMapper.xml映射文件：

<?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"><!-- 結果映射 --><resultMap id="userResultMap" type="User"><id property="id" column="id"/><result property="username" column="username"/><result property="email" column="email"/><result property="age" column="age"/><result property="createdTime" column="created_time"/></resultMap><!-- 插入用戶 --><insert id="insertUser" parameterType="User" useGeneratedKeys="true" keyProperty="id">INSERT INTO user (username, email, age)VALUES (#{username}, #{email}, #{age})</insert><!-- 根據ID刪除用戶 --><delete id="deleteUserById" parameterType="int">DELETE FROM user WHERE id = #{id}</delete><!-- 更新用戶信息 --><update id="updateUser" parameterType="User">UPDATE user SETusername = #{username},email = #{email},age = #{age}WHERE id = #{id}</update><!-- 根據ID查詢用戶 --><select id="selectUserById" parameterType="int" resultMap="userResultMap">SELECT id, username, email, age, created_timeFROM userWHERE id = #{id}</select><!-- 查詢所有用戶 --><select id="selectAllUsers" resultMap="userResultMap">SELECT id, username, email, age, created_timeFROM userORDER BY created_time DESC</select><!-- 根據用戶名查詢用戶 --><select id="selectUsersByUsername" parameterType="string" resultMap="userResultMap">SELECT id, username, email, age, created_timeFROM userWHERE username LIKE CONCAT('%', #{username}, '%')</select></mapper>

工具類

創建MyBatis工具類：

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 {// 讀取配置文件InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");// 創建SqlSessionFactorysqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) {e.printStackTrace();}}// 獲取SqlSessionpublic static SqlSession getSqlSession() {return sqlSessionFactory.openSession();}// 獲取自動提交的SqlSessionpublic static SqlSession getSqlSession(boolean autoCommit) {return sqlSessionFactory.openSession(autoCommit);}
}

測試類

創建測試類驗證CRUD操作：

package com.example.test;import com.example.entity.User;
import com.example.mapper.UserMapper;
import com.example.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;import java.util.List;public class MyBatisTest {public static void main(String[] args) {// 測試插入testInsert();// 測試查詢testSelect();// 測試更新testUpdate();// 測試刪除testDelete();}// 測試插入public static void testInsert() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user = new User("張三", "zhangsan@example.com", 25);int result = mapper.insertUser(user);sqlSession.commit();System.out.println("插入結果: " + result + ", 用戶ID: " + user.getId());} finally {sqlSession.close();}}// 測試查詢public static void testSelect() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);// 查詢所有用戶List<User> users = mapper.selectAllUsers();System.out.println("所有用戶: " + users);// 根據ID查詢if (!users.isEmpty()) {User user = mapper.selectUserById(users.get(0).getId());System.out.println("根據ID查詢: " + user);}} finally {sqlSession.close();}}// 測試更新public static void testUpdate() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> users = mapper.selectAllUsers();if (!users.isEmpty()) {User user = users.get(0);user.setAge(30);user.setEmail("updated@example.com");int result = mapper.updateUser(user);sqlSession.commit();System.out.println("更新結果: " + result);}} finally {sqlSession.close();}}// 測試刪除public static void testDelete() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> users = mapper.selectAllUsers();if (!users.isEmpty()) {int result = mapper.deleteUserById(users.get(0).getId());sqlSession.commit();System.out.println("刪除結果: " + result);}} finally {sqlSession.close();}}
}

動態SQL

MyBatis提供了強大的動態SQL功能，可以根據條件動態生成SQL語句：

常用標簽

<!-- if標簽：條件判斷 -->
<select id="selectUsersByCondition" parameterType="User" resultMap="userResultMap">SELECT * FROM userWHERE 1=1<if test="username != null and username != ''">AND username LIKE CONCAT('%', #{username}, '%')</if><if test="email != null and email != ''">AND email = #{email}</if><if test="age != null">AND age = #{age}</if>
</select><!-- where標簽：智能處理WHERE關鍵字和AND/OR -->
<select id="selectUsersWithWhere" parameterType="User" resultMap="userResultMap">SELECT * FROM user<where><if test="username != null and username != ''">username LIKE CONCAT('%', #{username}, '%')</if><if test="email != null and email != ''">AND email = #{email}</if><if test="age != null">AND age = #{age}</if></where>
</select><!-- choose、when、otherwise：類似switch語句 -->
<select id="selectUsersByChoose" parameterType="User" resultMap="userResultMap">SELECT * FROM user<where><choose><when test="username != null and username != ''">username LIKE CONCAT('%', #{username}, '%')</when><when test="email != null and email != ''">email = #{email}</when><otherwise>age &gt; 18</otherwise></choose></where>
</select><!-- set標簽：用于UPDATE語句 -->
<update id="updateUserSelective" parameterType="User">UPDATE user<set><if test="username != null and username != ''">username = #{username},</if><if test="email != null and email != ''">email = #{email},</if><if test="age != null">age = #{age}</if></set>WHERE id = #{id}
</update><!-- foreach標簽：循環處理集合 -->
<select id="selectUsersByIds" parameterType="list" resultMap="userResultMap">SELECT * FROM userWHERE id IN<foreach collection="list" item="id" open="(" separator="," close=")">#{id}</foreach>
</select>

高級特性

一對一關聯映射

<!-- 用戶訂單一對一關系 -->
<resultMap id="userWithOrderResultMap" type="User"><id property="id" column="user_id"/><result property="username" column="username"/><association property="order" javaType="Order"><id property="id" column="order_id"/><result property="orderNo" column="order_no"/><result property="amount" column="amount"/></association>
</resultMap><select id="selectUserWithOrder" resultMap="userWithOrderResultMap">SELECT u.id as user_id, u.username, o.id as order_id, o.order_no, o.amountFROM user uLEFT JOIN order o ON u.id = o.user_idWHERE u.id = #{id}
</select>

一對多關聯映射

<!-- 用戶訂單一對多關系 -->
<resultMap id="userWithOrdersResultMap" type="User"><id property="id" column="user_id"/><result property="username" column="username"/><collection property="orders" ofType="Order"><id property="id" column="order_id"/><result property="orderNo" column="order_no"/><result property="amount" column="amount"/></collection>
</resultMap><select id="selectUserWithOrders" resultMap="userWithOrdersResultMap">SELECT u.id as user_id, u.username,o.id as order_id, o.order_no, o.amountFROM user uLEFT JOIN order o ON u.id = o.user_idWHERE u.id = #{id}
</select>

分頁查詢

<!-- 分頁查詢 -->
<select id="selectUsersWithPage" parameterType="map" resultMap="userResultMap">SELECT * FROM userORDER BY created_time DESCLIMIT #{offset}, #{pageSize}
</select><!-- 查詢總數 -->
<select id="countUsers" resultType="int">SELECT COUNT(*) FROM user
</select>

使用注解方式

public interface UserMapper {@Insert("INSERT INTO user (username, email, age) VALUES (#{username}, #{email}, #{age})")@Options(useGeneratedKeys = true, keyProperty = "id")int insertUserWithAnnotation(User user);@Delete("DELETE FROM user WHERE id = #{id}")int deleteUserByIdWithAnnotation(@Param("id") Integer id);@Update("UPDATE user SET username = #{username}, email = #{email}, age = #{age} WHERE id = #{id}")int updateUserWithAnnotation(User user);@Select("SELECT * FROM user WHERE id = #{id}")@Results({@Result(property = "id", column = "id"),@Result(property = "username", column = "username"),@Result(property = "email", column = "email"),@Result(property = "age", column = "age"),@Result(property = "createdTime", column = "created_time")})User selectUserByIdWithAnnotation(@Param("id") Integer id);
}