C
SY247
CSY247
DrinkWater
VsBackground
MarkdownInSider
在 SpringBoot 应用中，依赖注入（Dependency Injection）允许对象从外部接收其依赖项，而不是自己创建它们。而 @Autowired 注解则是实现依赖注入的关键工具，它用于自动装配 Spring 容器中的 bean，可以应用于构造器、方法、参数和字段上。
这是最简单直接的注入方式，直接在字段上使用注解：
@Service
public class UserService {
@Autowired
private UserRepository userRepository;
public User findUserById(Long id) {
return userRepository.findById(id).orElse(null);
}
}代码简洁，易于阅读；
不需要 setter 方法或构造器
不利于单元测试（需要使用反射）；
隐藏了依赖关系；
不符合不可变对象原则；
Spring 官方推荐的方式，通过构造器进行注入：
@Service
public class OrderService {
private final PaymentService paymentService;
private final NotificationService notificationService;
@Autowired
public OrderService(PaymentService paymentService, NotificationService notificationService) {
this.paymentService = paymentService;
this.notificationService = notificationService;
}
// 从Spring 4.3开始，单一构造器可以省略@Autowired
public OrderService(PaymentService paymentService) {
this.paymentService = paymentService;
this.notificationService = null;
}
}明确依赖关系，一目了然；
便于单元测试；
支持不可变对象（final 字段）；
通过 setter 方法进行注入：
@Service
public class ProductService {
private InventoryService inventoryService;
private PricingService pricingService;
@Autowired // 需要注解才会装入
public void setInventoryService(InventoryService inventoryService) {
this.inventoryService = inventoryService;
}
public void setPricingService(PricingService pricingService) {
this.pricingService = pricingService;
}
}允许在 bean 创建后重新配置；
可选依赖时比较有用；
可以注入到任意方法中（和 setter 差不多）：
@Component
public class DataInitializer {
private DataSource dataSource;
@Autowired
public void prepareDataSource(DataSource dataSource) {
this.dataSource = dataSource;
// 初始化数据源配置
}
}当依赖不是必须时，可以使用 required=false：
@Service
public class ReportService {
@Autowired(required = false)
private EmailService emailService;
public void generateReport() {
// 业务逻辑
if (emailService != null) {
emailService.sendReport();
}
}
}当有多个相同类型的 bean 时，Spring 需要明确知道注入哪一个：
@Configuration
public class AppConfig {
@Bean
@Primary // 优先使用这个bean
public PaymentService creditCardPaymentService() {
return new CreditCardPaymentService();
}
@Bean
public PaymentService paypalPaymentService() {
return new PayPalPaymentService();
}
}
@Service
public class CheckoutService {
@Autowired // 会自动注入CreditCardPaymentService
private PaymentService paymentService;
}@Configuration
public class AppConfig {
@Bean("creditCardPayment")
public PaymentService creditCardPaymentService() {
return new CreditCardPaymentService();
}
@Bean("paypalPayment")
public PaymentService paypalPaymentService() {
return new PayPalPaymentService();
}
}
@Service
public class CheckoutService {
@Autowired
@Qualifier("paypalPayment") // 明确指定bean名称
private PaymentService paymentService;
}Spring 支持注入集合类型：
@Service
public class NotificationDispatcher {
// 注入所有NotificationSender实现
@Autowired
private List<NotificationSender> senders;
// 注入Map，key为bean名称
@Autowired
private Map<String, NotificationSender> senderMap;
public void sendNotifications(String message) {
senders.forEach(sender -> sender.send(message));
}
}✨相关推荐✨