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>
370 lines
7.7 KiB
Markdown
370 lines
7.7 KiB
Markdown
# Spring Boot 核心原理
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## 问题
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1. Spring Boot 的自动配置原理是什么？
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2. @SpringBootApplication 注解包含哪些核心注解？
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3. Spring Boot 的启动流程是怎样的？
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4. 什么是条件注解（@Conditional）？
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5. Spring Boot 如何实现配置文件加载？
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6. Spring Boot 的健康检查和监控如何实现？
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7. Spring Boot 的 Starter 原理是什么？
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---
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## 标准答案
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### 1. @SpringBootApplication 注解
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```java
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@SpringBootConfiguration // 1. 配置类
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@EnableAutoConfiguration // 2. 自动配置
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@ComponentScan // 3. 组件扫描
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public @interface SpringBootApplication {
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}
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```
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---
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#### **1. @SpringBootConfiguration**
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```java
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@Configuration // 本质上是 @Configuration
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public @interface SpringBootConfiguration {
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}
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```
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**作用**：标记为配置类（等同于 XML 配置文件）
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---
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#### **2. @EnableAutoConfiguration**
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```java
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@AutoConfigurationPackage // 自动配置包
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@Import(AutoConfigurationImportSelector.class) // 导入自动配置类
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public @interface EnableAutoConfiguration {
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}
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```
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**核心**：`AutoConfigurationImportSelector`
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```java
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// 加载 META-INF/spring.factories 中的自动配置类
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String[] configurations = SpringFactoriesLoader.loadFactoryNames(
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getSpringFactoriesLoaderFactoryClass(),
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getBeanClassLoader()
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);
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```
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---
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#### **3. @ComponentScan**
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```java
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@ComponentScan(
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excludeFilters = { // 排除过滤器
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@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
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@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class)
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}
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)
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```
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**作用**：扫描 `@Component`、`@Service`、`@Repository`、`@Controller` 等注解
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---
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### 2. 自动配置原理
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#### **核心流程**
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```
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1. @EnableAutoConfiguration
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↓
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2. 加载 META-INF/spring.factories
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↓
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3. 根据 @Conditional 条件注解决定是否加载配置
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↓
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4. 注册 Bean
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```
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---
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#### **spring.factories 示例**
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```properties
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# spring-boot-autoconfigure-2.7.0.jar
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org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
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org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
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org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
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org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
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...
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```
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---
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#### **条件注解示例**
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```java
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@Configuration
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@ConditionalOnClass(DataSource.class) // 类路径存在 DataSource
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@ConditionalOnMissingBean(DataSource.class) // 容器中不存在 DataSource Bean
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@EnableConfigurationProperties(DataSourceProperties.class)
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public class DataSourceAutoConfiguration {
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@Bean
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public DataSource dataSource(DataSourceProperties properties) {
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// 创建 DataSource
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return properties.initializeDataSourceBuilder().build();
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}
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}
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```
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---
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### 3. Spring Boot 启动流程
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```java
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@SpringBootApplication
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public class Application {
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public static void main(String[] args) {
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SpringApplication.run(Application.class, args);
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}
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}
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```
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---
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#### **核心步骤**
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```
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1. 创建 SpringApplication
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↓
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2. 准备 Environment
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↓
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3. 打印 Banner
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↓
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4. 创建 ApplicationContext
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↓
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5. 刷新 Context（加载 Bean）
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↓
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6. 调用 Runner（ApplicationRunner、CommandLineRunner）
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```
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---
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#### **源码分析**
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```java
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public SpringApplication(Class<?>... primarySources) {
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// 1. 保存主配置类
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this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
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// 2. 推断 Web 应用类型（SERVLET、REACTIVE、NONE）
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this.webApplicationType = WebApplicationType.deduceFromClasspath();
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// 3. 加载 ApplicationContextInitializer
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setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
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// 4. 加载 ApplicationListener
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setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
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// 5. 推断主类（main 方法所在类）
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this.mainApplicationClass = deduceMainApplicationClass();
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}
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```
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---
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### 4. 配置文件加载
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#### **加载顺序**
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```
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1. 命令行参数（--server.port=8081）
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2. Java 系统属性（System.getProperties()）
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3. 操作系统环境变量
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4. JAR 外部的 application-{profile}.properties
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5. JAR 内部的 application-{profile}.properties
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6. JAR 外部的 application.properties
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7. JAR 内部的 application.properties
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8. @PropertySource
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9. 默认属性（SpringApplication.setDefaultProperties）
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```
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---
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#### **配置文件示例**
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```yaml
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# application.yml
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server:
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port: 8080
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spring:
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profiles:
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active: dev
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---
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spring:
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config:
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activate:
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on-profile: dev
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datasource:
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url: jdbc:mysql://localhost:3306/dev
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---
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spring:
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config:
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activate:
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on-profile: prod
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datasource:
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url: jdbc:mysql://prod-db:3306/prod
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```
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---
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### 5. 自定义 Starter
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#### **步骤**
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**1. 创建 autoconfigure 模块**：
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```java
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@Configuration
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@ConditionalOnClass(HelloService.class)
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@EnableConfigurationProperties(HelloProperties.class)
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public class HelloAutoConfiguration {
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@Bean
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@ConditionalOnMissingBean
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public HelloService helloService(HelloProperties properties) {
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return new HelloService(properties.getMessage());
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}
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}
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```
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**2. 创建配置类**：
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```java
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@ConfigurationProperties(prefix = "hello")
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public class HelloProperties {
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private String message = "Hello World";
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// getter/setter
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}
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```
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**3. 创建 spring.factories**：
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```properties
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# META-INF/spring.factories
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org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
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com.example.hello.HelloAutoConfiguration
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```
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**4. 使用**：
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```yaml
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# application.yml
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hello:
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message: Hello Spring Boot
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```
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```java
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@Autowired
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private HelloService helloService;
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helloService.sayHello(); // 输出：Hello Spring Boot
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```
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---
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### 6. Actuator 监控
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#### **依赖**
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```xml
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-actuator</artifactId>
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</dependency>
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```
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---
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#### **配置**
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```yaml
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management:
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endpoints:
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web:
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exposure:
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include: health,info,metrics,prometheus # 暴露端点
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endpoint:
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health:
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show-details: always # 显示详细信息
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```
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---
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#### **常用端点**
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| 端点 | 说明 | 示例 |
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|------|------|------|
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| **/actuator/health** | 健康检查 | `{"status":"UP"}` |
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| **/actuator/info** | 应用信息 | 版本、描述等 |
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| **/actuator/metrics** | 指标 | JVM、HTTP 请求等 |
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| **/actuator/prometheus** | Prometheus 格式 | 监控数据 |
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| **/actuator/env** | 环境变量 | 配置属性 |
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| **/actuator/loggers** | 日志配置 | 日志级别 |
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---
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#### **自定义健康检查**
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```java
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@Component
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public class DatabaseHealthIndicator implements HealthIndicator {
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@Autowired
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private DataSource dataSource;
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@Override
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public Health health() {
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try (Connection conn = dataSource.getConnection()) {
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if (conn.isValid(1)) {
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return Health.up()
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.withDetail("database", "MySQL")
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.build();
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}
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} catch (SQLException e) {
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return Health.down()
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.withException(e)
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.build();
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}
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}
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}
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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 Spring Boot 的条件装配机制
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- 理解 SpringApplication 的启动流程
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- 理解 AutoConfigurationImportSelector 的工作原理
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**实战经验**：
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- 有自定义 Starter 的经验
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- 有解决自动配置冲突的经验
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- 有 Spring Boot 性能优化的经验
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**架构能力**：
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- 能设计可复用的 Spring Boot Starter
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- 能设计多环境配置方案
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- 能设计微服务监控体系
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**技术选型**：
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- 了解 Spring Boot 2.x vs 3.x 的区别
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- 了解 GraalVM Native Image 的支持
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- 了解 Quarkus、Micronaut 等替代框架
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