// 沒有管家的苦日子
Employee developer = new Developer();
Employee manager = new Manager();
Project project = new Project(developer, manager);

// 有管家的幸福生活
@Autowired
private Project project; // 管家，幫我組建一個項目團隊！

// 啟動Spring容器（聘請管家）
ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
// 向管家索取需要的服務
ProjectService projectService = context.getBean(ProjectService.class);

@SpringBootApplication // ← 這就是聘書，包含三個重要指令
public class CompanyApplication {
    public static void main(String[] args) {
        SpringApplication.run(CompanyApplication.class, args); // 正式聘請管家
    }
}

@SpringBootConfiguration  // ← 指令1：這是家正規(guī)公司（配置類）
@EnableAutoConfiguration  // ← 指令2：管家可以自主決策（自動配置）
@ComponentScan            // ← 指令3：在公司內(nèi)尋找人才（組件掃描）
public class CompanyApplication {
    // ...
}

@Component         // ← 普通員工工牌
public class Developer {
    public void code() {
        System.out.println("編寫代碼...");
    }
}
@Service           // ← 管理層工牌（特殊待遇）
public class ProjectService {
    private final Developer developer;
    public ProjectService(Developer developer) {
        this.developer = developer;
    }
}
@Repository        // ← 倉庫管理員工牌（有錯誤轉(zhuǎn)換特權(quán)）
public class ProjectRepository {
    // 數(shù)據(jù)訪問邏輯
}
@Controller        // ← 前臺接待員工牌（處理外部請求）
public class ProjectController {
    private final ProjectService projectService;
    public ProjectController(ProjectService projectService) {
        this.projectService = projectService;
    }
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component // 所有注解都是@Component的特殊化
public @interface Service {
    // ...
}

@Service
public class ProjectService {
    // 方式1：字段注入（直接配助手）- 簡單但不推薦
    @Autowired
    private Developer developer;
    // 方式2：構(gòu)造器注入（招聘時指定助手）- 推薦方式
    private final Designer designer;
    @Autowired
    public ProjectService(Designer designer) {
        this.designer = designer; // 一旦配備，不可更改
    }
    // 方式3：Setter注入（后期配置設(shè)備）- 可選依賴
    private Printer printer;
    @Autowired
    public void setPrinter(Printer printer) {
        this.printer = printer; // 可以后期更換
    }
}

@Configuration // ← 人力資源部
public class CompanyConfig {
    @Bean // ← 手動簽發(fā)聘書
    public SpecialExpert specialExpert() {
        return new SpecialExpert(); // 來自第三方庫的專家
    }
    @Bean
    public ProjectTeam projectTeam(Developer developer, SpecialExpert expert) {
        // 管家會自動提供需要的依賴
        return new ProjectTeam(developer, expert);
    }
}

@Configuration
public class SmartConfiguration {
    // 只有當公司有數(shù)據(jù)庫時，才招聘DBA
    @Bean
    @ConditionalOnClass(DataSource.class)
    public DatabaseAdmin databaseAdmin() {
        return new DatabaseAdmin();
    }
    // 只有當需要處理Web請求時，才配備Web團隊
    @Bean
    @ConditionalOnWebApplication
    public WebTeam webTeam() {
        return new WebTeam();
    }
    // 只有當配置了郵件服務器時，才設(shè)立郵件部門
    @Bean
    @ConditionalOnProperty(name = "mail.host")
    public EmailService emailService() {
        return new EmailService();
    }
}

# spring.factories文件內(nèi)容
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaAutoConfiguration

@Configuration
@ConditionalOnClass(DataSource.class) // 有數(shù)據(jù)庫驅(qū)動才生效
@ConditionalOnProperty(prefix = "spring.datasource", name = "url") // 配置了URL才生效
@EnableConfigurationProperties(DataSourceProperties.class) // 綁定配置屬性
public class DataSourceAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean // 如果沒有自定義DataSource才創(chuàng)建
    public DataSource dataSource(DataSourceProperties properties) {
        return properties.initializeDataSourceBuilder().build();
    }
}

// 1. 啟動類（公司總部）
@SpringBootApplication
public class CompanyApplication {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(CompanyApplication.class, args);
        // 從容器中獲取bean
        Project project = context.getBean(Project.class);
        project.start();
    }
}
// 2. 服務層（管理部門）
@Service
public class ProjectService {
    private final Developer developer;
    private final Designer designer;
    // 構(gòu)造器注入
    public ProjectService(Developer developer, Designer designer) {
        this.developer = developer;
        this.designer = designer;
    }
    public void startProject() {
        developer.code();
        designer.design();
    }
}
// 3. 組件類（員工）
@Component
public class Developer {
    public void code() {
        System.out.println("程序員編寫代碼...");
    }
}
@Component
public class Designer {
    public void design() {
        System.out.println("設(shè)計師設(shè)計界面...");
    }
}
// 4. 配置類（人力資源部）
@Configuration
public class CompanyConfig {
    @Bean
    public Project project(ProjectService projectService) {
        return new Project(projectService);
    }
}
// 5. 項目類
public class Project {
    private final ProjectService projectService;
    public Project(ProjectService projectService) {
        this.projectService = projectService;
    }
    public void start() {
        System.out.println("項目啟動！");
        projectService.startProject();
    }
}