Spring中管理bean对象的方式(专业级说明)

<beans>
    <bean id="userService" class="com.example.UserServiceImpl"/>
    <!-- 作用域、依赖注入等配置 -->
    <bean id="dataSource" class="com.example.DataSource" scope="singleton">
        <property name="url" value="jdbc:mysql://localhost:3306/db"/>
    </bean>
</beans>

@Service  // 标记为Service层Bean
public class UserService {}
@Repository  // 标记为DAO层Bean
public class UserDao {}

@Configuration
public class AppConfig {
    @Bean
    public DataSource dataSource() {
        return new DriverManagerDataSource();
    }
}

@Configuration
@ComponentScan("com.example")  // 自动扫描包
public class AppConfig {
    @Bean
    @Scope("prototype")
    public MyBean myBean() {
        return new MyBean();
    }
}

@Bean
@Scope("prototype")
public MyPrototypeBean myPrototypeBean() {
    return new MyPrototypeBean();
}

@Component
public class LifecycleBean {
    @PostConstruct
    public void init() {
        System.out.println("Bean初始化");
    }
    @PreDestroy
    public void cleanup() {
        System.out.println("Bean销毁");
    }
}

@Component
public class CustomBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) {
        // 初始化前逻辑
        return bean;
    }
}

@Service
public class UserService {
    private final UserDao userDao;
    @Autowired  // Spring 4.3+可省略
    public UserService(UserDao userDao) {
        this.userDao = userDao;
    }
}

@Autowired
public void setUserDao(UserDao userDao) {
    this.userDao = userDao;
}

@Autowired
private UserDao userDao;

@Autowired
@Qualifier("mainDataSource")
private DataSource dataSource;

@Bean
@Lazy
public HeavyResource heavyResource() {
    return new HeavyResource();
}

// 基于注解的容器
AnnotationConfigApplicationContext context = 
    new AnnotationConfigApplicationContext(AppConfig.class);
UserService userService = context.getBean(UserService.class);
// 基于XML的容器
ClassPathXmlApplicationContext xmlContext =
    new ClassPathXmlApplicationContext("applicationContext.xml");