文章目录
- 第8章：从jdbc到MyBatis
- JDBC操作数据库
- 原生JDBC访问数据库缺点和ORM框架介绍
- Mybatis基础知识
- Spring+Mybatis快速入门
第8章：从jdbc到MyBatis
JDBC操作数据库
JDBC核心概念
- Java Database Connectivity（Java数据库连接）
- Java访问数据库的标准API
- 提供统一的数据库访问接口
JDBC核心组件
- DriverManager：驱动管理器
- Connection：数据库连接
- Statement/PreparedStatement：SQL语句执行器
- ResultSet：结果集
// 原生JDBC示例publicclassJdbcExample{publicstaticvoidmain(String[]args){Connectionconn=null;PreparedStatementpstmt=null;ResultSetrs=null;try{// 1. 加载数据库驱动Class.forName("com.mysql.cj.jdbc.Driver");// 2. 建立数据库连接conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/test_db","root","123456");// 3. 创建PreparedStatement执行SQLStringsql="SELECT id, name, age FROM user WHERE age > ?";pstmt=conn.prepareStatement(sql);pstmt.setInt(1,18);// 4. 执行查询并处理结果集rs=pstmt.executeQuery();while(rs.next()){intid=rs.getInt("id");Stringname=rs.getString("name");intage=rs.getInt("age");System.out.printf("ID: %d, Name: %s, Age: %d%n",id,name,age);}}catch(Exceptione){e.printStackTrace();}finally{// 5. 关闭资源try{if(rs!=null)rs.close();if(pstmt!=null)pstmt.close();if(conn!=null)conn.close();}catch(SQLExceptione){e.printStackTrace();}}}}原生JDBC访问数据库缺点和ORM框架介绍
原生JDBC的主要缺点
| 缺点 | 描述 | 影响 |
|---|---|---|
| 代码冗余 | 重复的创建连接、关闭资源代码 | 开发效率低，代码臃肿 |
| 硬编码 | SQL与Java代码混合 | 维护困难，可读性差 |
| 手动映射 | 需要手动将ResultSet映射为对象 | 容易出错，工作量大 |
| 异常处理 | 需要处理大量checked异常 | 代码繁琐，易遗漏 |
| 连接管理 | 手动管理数据库连接 | 性能差，资源泄露风险 |
ORM框架介绍
- Object-Relational Mapping（对象关系映射）
- 将数据库表与Java对象建立映射关系
- 自动完成对象与关系数据的转换
主流ORM框架对比
| 框架 | 优点 | 缺点 | 适用场景 |
|---|---|---|---|
| MyBatis | SQL灵活，学习成本低 | 需要手动编写SQL | 复杂SQL，性能要求高 |
| Hibernate | 全自动，功能强大 | 学习曲线陡峭，SQL优化难 | 简单CRUD，快速开发 |
| JPA | 标准规范，移植性好 | 功能相对简单 | 标准企业应用 |
Mybatis基础知识
MyBatis核心概念
- SqlSessionFactory：会话工厂，创建SqlSession
- SqlSession：数据库会话，执行SQL操作
- Mapper接口：数据访问接口
- Mapper XML：SQL映射文件
MyBatis架构层次
应用程序 ↓ Mapper接口 ↓ SqlSession ↓ Executor（执行器） ↓ StatementHandler ↓ 数据库MyBatis核心配置文件结构
<!-- mybatis-config.xml --><?xml version="1.0" encoding="UTF-8" ?><!DOCTYPEconfigurationPUBLIC"-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><settings><!-- 开启驼峰命名自动映射 --><settingname="mapUnderscoreToCamelCase"value="true"/></settings><typeAliases><!-- 类型别名配置 --><typeAliasalias="User"type="com.example.entity.User"/></typeAliases><environmentsdefault="development"><environmentid="development"><transactionManagertype="JDBC"/><dataSourcetype="POOLED"><propertyname="driver"value="com.mysql.cj.jdbc.Driver"/><propertyname="url"value="jdbc:mysql://localhost:3306/test_db"/><propertyname="username"value="root"/><propertyname="password"value="123456"/></dataSource></environment></environments><mappers><!-- Mapper文件配置 --><mapperresource="mapper/UserMapper.xml"/></mappers></configuration>Spring+Mybatis快速入门
项目配置
<!-- pom.xml --><dependencies><!-- SpringBoot Starter --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!-- MyBatis SpringBoot Starter --><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>3.0.3</version></dependency><!-- MySQL驱动 --><dependency><groupId>com.mysql</groupId><artifactId>mysql-connector-j</artifactId><scope>runtime</scope></dependency><!-- Lombok --><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency></dependencies>创建表和添加数据
CREATETABLEuser(id BIGINT AUTO_INCREMENTPRIMARYKEY,usernameVARCHAR(50)NOTNULLUNIQUE,emailVARCHAR(100)NOTNULLUNIQUE,age INT,create_timeDATETIME(6)DEFAULTCURRENT_TIMESTAMP(6),update_timeDATETIME(6)DEFAULTCURRENT_TIMESTAMP(6)ONUPDATECURRENT_TIMESTAMP(6),INDEXidx_username(username),INDEXidx_email(email),INDEXidx_create_time(create_time))ENGINE=InnoDBDEFAULTCHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;INSERTINTOuser(username,email,age)VALUES('zhangsan', 'zhangsan@example.com',25);INSERTINTOuser(username,email,age)VALUES('lisi','lisi@example.com',30);INSERTINTOuser(username,email,age)VALUES('wangwu','wangwu@example.com',28);INSERTINTOuser(username,email)VALUES('zhaoliu', 'zhaoliu@example.com');INSERTINTOuser(username,email,age)VALUES('sunqi','sunqi@example.com',35),('zhouba','zhouba@example.com',22),('wujiu','wujiu@example.com',29);应用配置文件
# application.ymlspring:datasource:url:jdbc:mysql://localhost:3306/mybatis_demousername:rootpassword:123456driver-class-name:com.mysql.cj.jdbc.Driver# MyBatis配置mybatis:# Mapper XML文件位置mapper-locations:classpath:mapper/*.xml# 实体类包路径type-aliases-package:com.example.entityconfiguration:# 开启驼峰命名自动映射map-underscore-to-camel-case:true# 控制台打印SQLlog-impl:org.apache.ibatis.logging.stdout.StdOutImpl实体类
// 用户实体类@DatapublicclassUser{privateLongid;privateStringusername;privateStringemail;privateIntegerage;privateLocalDateTimecreateTime;privateLocalDateTimeupdateTime;}mapper接口定义
@MapperpublicinterfaceUserMapper{/** * 根据ID查询用户 */UserfindById(Longid);/** * 查询所有用户 */List<User>findAll();/** * 根据用户名查询 */UserfindByUsername(Stringusername);}mapper xml配置
<!-- src/main/resources/mapper/UserMapper.xml --><?xml version="1.0" encoding="UTF-8" ?><!DOCTYPEmapperPUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mappernamespace="com.example.mapper.UserMapper"><!-- 根据ID查询用户 --><selectid="findById"parameterType="Long"resulType="com.xd.entity.User">SELECT id, username, email, age, create_time, update_time FROM users WHERE id = #{id}</select><!-- 查询所有用户 --><selectid="findAll"resulType="User">SELECT id, username, email, age, create_time, update_time FROM users ORDER BY id DESC</select><!-- 根据用户名查询 --><selectid="findByUsername"parameterType="String"resulType="User">SELECT id, username, email, age, create_time, update_time FROM users WHERE username = #{username}</select></mapper>service层实现
@ServicepublicclassUserService{@AutowiredprivateUserMapperuserMapper;/** * 根据ID获取用户 */publicUsergetUserById(Longid){returnuserMapper.findById(id);}/** * 获取所有用户 */publicList<User>getAllUsers(){returnuserMapper.findAll();}/** * 根据用户名查询用户 */publicUsergetUserByUsername(Stringusername){returnuserMapper.findByUsername(username);}}controller层实现
@RestController@RequestMapping("/api/users")publicclassUserController{@AutowiredprivateUserServiceuserService;/** * 根据ID查询用户 */@GetMapping("/{id}")publicResponseEntity<User>getUserById(@PathVariableLongid){Useruser=userService.getUserById(id);returnResponseEntity.ok(user);}/** * 查询所有用户 */@GetMappingpublicResponseEntity<List<User>>getAllUsers(){List<User>users=userService.getAllUsers();returnResponseEntity.ok(users);}}配置SQLSessionFactory
@ConfigurationpublicclassMyBatisConfig{@BeanpublicSqlSessionFactorysqlSessionFactory(DataSourcedataSource)throwsException{SqlSessionFactoryBeansessionFactory=newSqlSessionFactoryBean();sessionFactory.setDataSource(dataSource);// 注入数据源// 设置Mapper XML路径sessionFactory.setMapperLocations(newPathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));sessionFactory.setTypeAliasesPackage("com.xd.springbootmybatis.entity");org.apache.ibatis.session.Configurationconfiguration=neworg.apache.ibatis.session.Configuration();configuration.setMapUnderscoreToCamelCase(true);configuration.setLogImpl(StdOutImpl.class);sessionFactory.setConfiguration(configuration);returnsessionFactory.getObject();}}请求结果
2026-01-22T10:28:36.101+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : === 进入拦截器 === 2026-01-22T10:28:36.101+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : 请求URL: /api/users 2026-01-22T10:28:36.101+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : 请求方法: GET Creating a new SqlSession SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@2aefc5b9] was not registered for synchronization because synchronization is not active JDBC Connection [HikariProxyConnection@606613140 wrapping com.mysql.cj.jdbc.ConnectionImpl@28fa08c] will not be managed by Spring ==> Preparing: SELECT id, username, email, age, create_time, update_time FROM user2 ORDER BY id DESC ==> Parameters: <== Columns: id, username, email, age, create_time, update_time <== Row: 7, wujiu, wujiu@example.com, 29, 2026-01-22 10:28:18.937905, 2026-01-22 10:28:18.937905 <== Row: 6, zhouba, zhouba@example.com, 22, 2026-01-22 10:28:18.937905, 2026-01-22 10:28:18.937905 <== Row: 5, sunqi, sunqi@example.com, 35, 2026-01-22 10:28:18.937905, 2026-01-22 10:28:18.937905 <== Row: 4, zhaoliu, zhaoliu@example.com, null, 2026-01-22 10:28:18.936642, 2026-01-22 10:28:18.936642 <== Row: 3, wangwu, wangwu@example.com, 28, 2026-01-22 10:28:18.934671, 2026-01-22 10:28:18.934671 <== Row: 2, lisi, lisi@example.com, 30, 2026-01-22 10:28:18.932989, 2026-01-22 10:28:18.932989 <== Row: 1, zhangsan, zhangsan@example.com, 25, 2026-01-22 10:28:18.926275, 2026-01-22 10:28:18.926275 <== Total: 7 Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@2aefc5b9] 2026-01-22T10:28:36.105+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : === 控制器执行完成 === 2026-01-22T10:28:36.105+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : === 请求处理完成 === ngsan, zhangsan@example.com, 25, 2026-01-22 10:28:18.926275, 2026-01-22 10:28:18.926275 <== Total: 7 Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@2aefc5b9] 2026-01-22T10:28:36.105+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : === 控制器执行完成 === 2026-01-22T10:28:36.105+08:00 INFO 17556 --- [nio-8080-exec-9] c.g.interceptor.LoginInterceptor : === 请求处理完成 ===
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