0e46a367c4
Organized 50 interview questions into 12 categories: - 01-分布式系统 (9 files): 分布式事务, 分布式锁, 一致性哈希, CAP理论, etc. - 02-数据库 (2 files): MySQL索引优化, MyBatis核心原理 - 03-缓存 (5 files): Redis数据结构, 缓存问题, LRU算法, etc. - 04-消息队列 (1 file): RocketMQ/Kafka - 05-并发编程 (4 files): 线程池, 设计模式, 限流策略, etc. - 06-JVM (1 file): JVM和垃圾回收 - 07-系统设计 (8 files): 秒杀系统, 短链接, IM, Feed流, etc. - 08-算法与数据结构 (4 files): B+树, 红黑树, 跳表, 时间轮 - 09-网络与安全 (3 files): TCP/IP, 加密安全, 性能优化 - 10-中间件 (4 files): Spring Boot, Nacos, Dubbo, Nginx - 11-运维 (4 files): Kubernetes, CI/CD, Docker, 可观测性 - 12-面试技巧 (1 file): 面试技巧和职业规划 All files renamed to Chinese for better accessibility and organized into categorized folders for easier navigation. Generated with [Claude Code](https://claude.com/claude-code) via [Happy](https://happy.engineering) Co-Authored-By: Claude <noreply@anthropic.com> Co-Authored-By: Happy <yesreply@happy.engineering>
178 lines
3.6 KiB
Markdown
178 lines
3.6 KiB
Markdown
# MyBatis 核心原理
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## 问题
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1. MyBatis 的核心组件有哪些？
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2. MyBatis 的缓存机制（一级缓存、二级缓存）？
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3. MyBatis 的插件原理是什么？
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4. #{} 和 ${} 的区别是什么？
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5. MyBatis 如何处理批量操作？
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6. MyBatis 的动态 SQL 是如何实现的？
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---
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## 标准答案
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### 1. MyBatis 核心组件
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```
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Configuration（全局配置）
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↓
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SqlSession（会话）
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↓
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Executor（执行器）
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↓
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StatementHandler（语句处理器）
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↓
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ParameterHandler（参数处理器）
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↓
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ResultSetHandler（结果集处理器）
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```
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---
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### 2. 缓存机制
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**一级缓存（SqlSession 级别）**：
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```java
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SqlSession session = sqlSessionFactory.openSession();
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User user1 = session.selectOne("selectUser", 1);
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User user2 = session.selectOne("selectUser", 1); // 从缓存获取
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```
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**二级缓存（Mapper 级别）**：
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```xml
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<!-- 开启二级缓存 -->
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<cache/>
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```
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```java
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User user1 = session1.selectOne("selectUser", 1);
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session1.close(); // 一级缓存清空，写入二级缓存
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User user2 = session2.selectOne("selectUser", 1); // 从二级缓存获取
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```
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---
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### 3. 插件原理
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**拦截的四大组件**：
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- Executor
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- StatementHandler
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- ParameterHandler
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- ResultSetHandler
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**示例**：
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```java
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@Intercepts({
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@Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class})
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})
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public class SqlInterceptor implements Interceptor {
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@Override
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public Object intercept(Invocation invocation) throws Throwable {
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// 前置逻辑
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Object result = invocation.proceed();
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// 后置逻辑
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return result;
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}
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}
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```
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---
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### 4. #{} vs ${}
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| 特性 | #{} | ${} |
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|------|-----|-----|
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| **预处理** | 是（PreparedStatement） | 否（Statement） |
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| **SQL 注入** | 安全 | 不安全 |
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| **类型转换** | 自动 | 需手动 |
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| **动态表名/列名** | 不支持 | 支持 |
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**示例**：
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```xml
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<!-- ✅ 安全 -->
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SELECT * FROM users WHERE id = #{id}
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<!-- ❌ SQL 注入风险 -->
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SELECT * FROM users WHERE id = ${id}
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<!-- ✅ 动态表名（只能用 ${}）-->
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SELECT * FROM ${tableName} WHERE id = #{id}
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```
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---
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### 5. 批量操作
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**方式 1：SqlSession 批量**：
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```java
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SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH);
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try {
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UserMapper mapper = session.getMapper(UserMapper.class);
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for (User user : users) {
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mapper.insert(user);
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}
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session.commit();
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} finally {
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session.close();
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}
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```
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**方式 2：Batch Insert**：
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```xml
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<insert id="batchInsert">
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INSERT INTO users (name, email) VALUES
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<foreach collection="users" item="user" separator=",">
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(#{user.name}, #{user.email})
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</foreach>
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</insert>
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```
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---
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### 6. 动态 SQL
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**常用标签**：
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```xml
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<select id="findUsers" resultType="User">
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SELECT * FROM users
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<where>
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<if test="name != null">
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AND name = #{name}
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</if>
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<if test="email != null">
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AND email = #{email}
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</if>
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</where>
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</select>
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<select id="findUsersByIds" resultType="User">
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SELECT * FROM users
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WHERE id IN
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<foreach collection="ids" item="id" open="(" separator="," close=")">
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#{id}
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</foreach>
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</select>
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```
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---
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### 7. 阿里 P7 加分项
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**深度理解**：
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- 理解 MyBatis 的代理机制（MapperProxy）
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- 理解二级缓存的并发问题
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- 理解插件的责任链模式
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**实战经验**：
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- 有处理 MyBatis 性能问题的经验
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- 有自定义插件的经验
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- 有 MyBatis 与 Spring 集成的经验
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**架构能力**：
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- 能设计多数据源方案
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- 能设计分库分表的 MyBatis 方案
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- 能设计 MyBatis 监控体系
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