// 預設只掃描啟動類所在套件及子套件
@SpringBootApplication
@ComponentScan("com.example") // 明確指定
public class Application { }

@Service
public class ServiceImpl {
    // Spring 會嘗試找一個 String 類型的 Bean 來注入
    public ServiceImpl(String serviceName) {
        this.serviceName = serviceName;
    }
}

// 解決：提供對應的 Bean
@Bean
public String serviceName() {
    return "MyServiceName";
}

// 方案 1：標記 @Primary
@Repository
@Primary
public class OracleDataService implements DataService { }

// 方案 2：使用 @Qualifier
@Autowired
@Qualifier("oracleDataService")
private DataService dataService;

// 方案 3：變數名與 Bean 名一致
@Autowired
private DataService oracleDataService;

// CassandraDataService -> cassandraDataService
// SQLiteDataService -> SQLiteDataService (連續大寫)

@Autowired
@Qualifier("cassandraDataService") // 注意首字母小寫
private DataService dataService;

public class StudentController {
    @Repository
    public static class InnerClassDataService implements DataService { }
}

// 引用方式
@Autowired
@Qualifier("studentController.InnerClassDataService")
private DataService innerClassDataService;

# application.properties
# 錯誤：username 可能與系統環境變數衝突
username=admin

# 正確：使用有前綴的唯一名稱
app.username=admin

@Service
public class MyService {
    @Autowired
    private MyService self; // 注入代理物件

    public void methodA() {
        self.methodB(); // 通過代理呼叫
    }
}

@Transactional
public void createOrder() {
    try {
        orderDao.insert(order);
    } catch (Exception e) {
        log.error("失敗", e);
        // 方案 1：重新拋出
        throw e;
        // 方案 2：手動標記回滾
        // TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();
    }
}

@Transactional(rollbackFor = Exception.class)
public void createOrder() throws Exception { }

java -jar myapp.jar --debug
# 或在 application.properties 中：
# debug=true

@Configuration
@ConditionalOnProperty(name = "feature.enabled", havingValue = "true")
public class FeatureConfig { }

@ConfigurationProperties(prefix = "myapp")
@Data
public class MyAppProperties {
    private String name;
}

// 啟用組態屬性
@SpringBootApplication
@EnableConfigurationProperties(MyAppProperties.class)
public class Application { }

# 以下格式都可以綁定到 firstName 屬性
myapp.first-name=John
myapp.firstName=John
myapp.first_name=John

┌─────────────────────────────────────────────────────────────┐
│                    Bean 相關啟動錯誤                          │
├─────────────────────────────────────────────────────────────┤
│ "No qualifying bean" → 檢查 @ComponentScan、包結構          │
│ "required a single bean, but N were found" → 用 @Qualifier  │
│ "Error creating bean" → 檢查依賴、構造器參數                 │
│ "BeanCurrentlyInCreationException" → 循環依賴               │
└─────────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────────┐
│                    執行時常見問題                             │
├─────────────────────────────────────────────────────────────┤
│ AOP 不生效 → 檢查是否 this 呼叫、是否 public 方法           │
│ 事務不回滾 → 檢查例外類型、是否被 catch                     │
│ 請求 404 → 檢查 URL 映射、掃描範圍                          │
│ 請求 400 → 檢查參數類型、格式、驗證                         │
│ 請求 500 → 查看例外堆疊                                     │
└─────────────────────────────────────────────────────────────┘

# application.yml
logging:
  level:
    org.springframework: DEBUG
    org.springframework.web: DEBUG
    org.springframework.transaction: TRACE

@Autowired
private ApplicationContext context;

public void checkBeans() {
    // 列出所有 Bean
    String[] beanNames = context.getBeanDefinitionNames();

    // 檢查特定類型的 Bean
    Map<String, DataService> beans = context.getBeansOfType(DataService.class);
}

@Autowired
private MyService myService;

public void checkProxy() {
    System.out.println("Is proxy: " + AopUtils.isAopProxy(myService));
    System.out.println("Is CGLIB proxy: " + AopUtils.isCglibProxy(myService));
    System.out.println("Is JDK proxy: " + AopUtils.isJdkDynamicProxy(myService));
}

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

Positive matches:
-----------------
   DataSourceAutoConfiguration matched:
      - @ConditionalOnClass found required classes ...

Negative matches:
-----------------
   ActiveMQAutoConfiguration:
      - @ConditionalOnClass did not find required class ...