第 3 課：自動設定、Spring IoC 容器和應用程式屬性

Spring Boot 4：從基礎到高級

第 1 部分：Spring Boot 平台

亞洲開發網

簡介

自動配置是Spring Boot區別於純Spring框架的「魔力」。了解它的工作原理將幫助您有效地調試並根據需要自訂應用程式。在本文中，我們將探討 IoC 容器、自動設定機制以及如何管理應用程式設定。

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1. 控制反轉 (IoC) 容器

1.1 什麼是國際奧委會？

在傳統程式設計中，您的程式碼會建立並管理物件：

// Truyền thống: bạn tạo dependencies
public class OrderService {
    private final OrderRepository repository = new OrderRepository();
    private final EmailService emailService = new EmailService();
}

透過 IoC，框架管理物件的創建：

// IoC: framework inject dependencies
@Service
public class OrderService {
    private final OrderRepository repository;
    private final EmailService emailService;

    // Spring tự động inject các dependencies
    public OrderService(OrderRepository repository, EmailService emailService) {
        this.repository = repository;
        this.emailService = emailService;
    }
}

1.2 ApplicationContext 與 BeanFactory

Spring IoC容器有2個主要介面：

BeanFactory (interface)
  └── ApplicationContext (interface, extends BeanFactory)
        ├── AnnotationConfigApplicationContext
        ├── GenericWebApplicationContext
        └── ...

特點	豆工廠	應用程式上下文
Bean 實例化	懶惰	渴望（預設）
活動發布	沒有	是的
AOP 支援	限制	完整
國際化	沒有	是的
環境抽象	沒有	是的

事實上，總是使用 ApplicationContext。

1.3 Bean註冊

// Cách 1: Stereotype Annotations (phổ biến nhất)
@Component      // Generic component
@Service        // Business logic
@Repository     // Data access
@Controller     // Web controller
@RestController // REST API controller
@Configuration  // Configuration class

// Cách 2: @Bean method trong @Configuration
@Configuration
public class AppConfig {

    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper()
            .registerModule(new JavaTimeModule())
            .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    }

    @Bean
    public RestClient restClient() {
        return RestClient.builder()
            .baseUrl("https://api.example.com")
            .build();
    }
}

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2. 自動設定深入探討

2.1 作用機制

自動配置基於啟動時對條件的評估：

Application Start
    │
    ▼
@SpringBootApplication
    │
    ├── @EnableAutoConfiguration
    │       │
    │       ▼
    │   META-INF/spring/
    │   org.springframework.boot.autoconfigure.AutoConfiguration.imports
    │       │
    │       ▼
    │   Evaluate @Conditional annotations
    │       │
    │       ├── @ConditionalOnClass → Class có trong classpath?
    │       ├── @ConditionalOnMissingBean → Bean đã tồn tại chưa?
    │       ├── @ConditionalOnProperty → Property có được set?
    │       └── @ConditionalOnWebApplication → Có phải web app?
    │       │
    │       ▼
    │   Create & Register Beans
    │
    ▼
Application Ready

2.2 範例：資料來源自動配置

當你加入 spring-boot-starter-data-jpa 和 PostgreSQL 驅動程式：

// Spring Boot tự động detect và tạo configuration tương tự:
@AutoConfiguration
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@EnableConfigurationProperties(DataSourceProperties.class)
public class DataSourceAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public DataSource dataSource(DataSourceProperties properties) {
        return properties.initializeDataSourceBuilder().build();
    }
}

Spring Boot 將：

1. 檢測 DataSource.class 在類路徑中→ @ConditionalOnClass = 真
2. 尚未進行檢查 DataSource 豆類 → @ConditionalOnMissingBean = 真
3. 讀取屬性 spring.datasource.* → 建立資料來源

2.3 查看自動設定報告

# Bật debug mode để xem report
debug=true

./mvnw spring-boot:run

輸出將顯示：

============================
CONDITIONS EVALUATION REPORT
============================

Positive matches:
-----------------
   DataSourceAutoConfiguration matched:
      - @ConditionalOnClass found required classes
        'javax.sql.DataSource', 'org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType'

Negative matches:
-----------------
   MongoAutoConfiguration:
      - @ConditionalOnClass did not find required class
        'com.mongodb.client.MongoClient'

2.4 自訂或停用自動配置

// Exclude cụ thể
@SpringBootApplication(exclude = {
    DataSourceAutoConfiguration.class,
    SecurityAutoConfiguration.class
})
public class MyApplication { }

// Hoặc trong properties
spring.autoconfigure.exclude=\
  org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration

---

3. 應用程式屬性和 YAML

3.1 屬性與 YAML

應用程式.屬性：

server.port=8080
spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
spring.datasource.username=admin
spring.datasource.password=secret
spring.jpa.hibernate.ddl-auto=update

application.yaml（或.yml）：

server:
  port: 8080

spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/mydb
    username: admin
    password: secret
  jpa:
    hibernate:
      ddl-auto: update

兩種格式均支援。 YAML 對於巢狀配置更具可讀性，但屬性更常見。

3.2 自訂屬性

// Định nghĩa properties class
@ConfigurationProperties(prefix = "app")
public record AppProperties(
    String name,
    String version,
    Security security
) {
    public record Security(
        String jwtSecret,
        long jwtExpirationMs,
        long refreshExpirationMs
    ) {}
}

# application.yaml
app:
  name: My Application
  version: 1.0.0
  security:
    jwt-secret: my-256-bit-secret-key-for-jwt-signing
    jwt-expiration-ms: 3600000
    refresh-expiration-ms: 86400000

// Enable và sử dụng
@SpringBootApplication
@EnableConfigurationProperties(AppProperties.class)
public class MyApplication { }

@Service
public class AuthService {
    private final AppProperties appProperties;

    public AuthService(AppProperties appProperties) {
        this.appProperties = appProperties;
        // appProperties.security().jwtSecret()
    }
}

3.3 財產來源與優先級

Spring Boot 會以優先權順序從多個來源讀取屬性：

1. Command line arguments (highest priority)
   java -jar app.jar --server.port=9090

2. OS Environment variables
   SERVER_PORT=9090

3. application-{profile}.properties
   application-prod.properties

4. application.properties
   src/main/resources/application.properties

5. @PropertySource annotations

6. Default properties (lowest priority)

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4. Profiles — 依照環境進行配置

4.1 設定檔的定義

# application.yaml (default, mọi môi trường)
spring:
  application:
    name: my-app

---
# application-dev.yaml
spring:
  config:
    activate:
      on-profile: dev
  datasource:
    url: jdbc:postgresql://localhost:5432/mydb_dev
  jpa:
    show-sql: true

---
# application-prod.yaml
spring:
  config:
    activate:
      on-profile: prod
  datasource:
    url: jdbc:postgresql://db-prod:5432/mydb_prod
  jpa:
    show-sql: false

4.2 啟動個人資料

# Cách 1: Command line
java -jar app.jar --spring.profiles.active=prod

# Cách 2: Environment variable
SPRING_PROFILES_ACTIVE=prod java -jar app.jar

# Cách 3: Trong application.properties
spring.profiles.active=dev

# Cách 4: Trong IDE
# Run Configuration → Environment variables → SPRING_PROFILES_ACTIVE=dev

4.3 特定於設定檔的 Bean

@Configuration
public class StorageConfig {

    @Bean
    @Profile("dev")
    public StorageService localStorageService() {
        return new LocalStorageService("/tmp/uploads");
    }

    @Bean
    @Profile("prod")
    public StorageService s3StorageService() {
        return new S3StorageService();
    }
}

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5. 外部化配置最佳實踐

5.1 無硬編碼秘密

# SAI - Không bao giờ commit secrets
spring:
  datasource:
    password: my-real-password

# ĐÚNG - Dùng environment variables
spring:
  datasource:
    password: ${DB_PASSWORD}

5.2 使用.env檔案進行本機開發

# .env (thêm vào .gitignore!)
DB_PASSWORD=local-dev-password
JWT_SECRET=dev-secret-key

5.3 屬性驗證

@ConfigurationProperties(prefix = "app")
@Validated
public record AppProperties(
    @NotBlank String name,
    @NotBlank String version,
    @Valid Security security
) {
    public record Security(
        @NotBlank String jwtSecret,
        @Positive long jwtExpirationMs
    ) {}
}

當缺少必需的屬性時，應用程式將快速失敗。

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總結

• IoC容器（ApplicationContext）管理bean的生命週期，透過建構子/setter/字段注入支援依賴注入
• 自動配置根據類別路徑依賴項和條件註解自動配置bean
• Spring Boot 兩者都支持 .properties 和 .yaml 格式，設定檔允許根據環境進行配置（dev/staging/prod）

練習

1. 開機 debug=true 在 application.properties 中，執行應用程式並分析 5 個匹配的自動配置（正匹配）
2. 創建 AppProperties 帶有前綴的記錄類 app，從application.yaml綁定3個自訂屬性並注入到控制器中顯示
3. 使用不同的資料庫 URL 建立 2 個設定檔（dev 和 prod），使用每個設定檔執行應用程式並驗證日誌輸出