Spring框架广泛应用了多种设计模式,以实现其灵活性、可扩展性和可维护性。以下是一些在Spring中常见的设计模式及其应用示例:
1. 单例模式(Singleton Pattern)
Spring中的Bean默认都是单例的,这意味着在整个应用上下文中,每个Bean定义只有一个实例。
java
@Service
public class SingletonService {
// 单例Bean的实现
}
2. 工厂模式(Factory Pattern)
Spring使用BeanFactory和ApplicationContext接口来创建和管理Bean实例,这是工厂模式的典型应用。
java
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
MyService myService = context.getBean(MyService.class);
3. 代理模式(Proxy Pattern)
Spring AOP(面向切面编程)通过代理模式实现,可以在不修改原有代码的情况下增强功能。
java
@Aspect
@Component
public class LoggingAspect {
@Before("execution(* com.example.service.*.*(..))")
public void logBefore(JoinPoint joinPoint) {
System.out.println("Executing: " + joinPoint.getSignature().getName());
}
}
4. 模板方法模式(Template Method Pattern)
Spring提供了多种模板类,如JdbcTemplate、RestTemplate等,这些模板类定义了一套固定的流程,但允许子类重写某些步骤。
java
public class JdbcCustomerDao {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
public Customer getCustomerById(int id) {
return jdbcTemplate.queryForObject("SELECT * FROM customers WHERE id = ?", new Object[]{id}, new CustomerRowMapper());
}
}
5. 观察者模式(Observer Pattern)
Spring的事件机制基于观察者模式,允许应用组件监听和响应特定事件。
java
public class CustomApplicationListener implements ApplicationListener<ContextRefreshedEvent> {
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
System.out.println("Application context has been initialized or refreshed.");
}
}
6. 策略模式(Strategy Pattern)
Spring的依赖注入机制允许开发者灵活地选择和切换不同的实现策略。
java
public interface PaymentStrategy {
void pay(int amount);
}
@Service
public class CreditCardPayment implements PaymentStrategy {
@Override
public void pay(int amount) {
System.out.println("Paid with credit card: " + amount);
}
}
@Service
public class PayPalPayment implements PaymentStrategy {
@Override
public void pay(int amount) {
System.out.println("Paid with PayPal: " + amount);
}
}
7. 装饰器模式(Decorator Pattern)
Spring Security中的认证和授权机制使用了装饰器模式,通过层层包装来增强功能。
java
public class CustomAuthenticationProvider implements AuthenticationProvider {
@Override
public Authentication authenticate(Authentication authentication) throws AuthenticationException {
// 自定义认证逻辑
return authentication;
}
@Override
public boolean supports(Class<?> authentication) {
return true;
}
}
- 适配器模式(Adapter Pattern)
Spring MVC中的HandlerAdapter接口允许不同的控制器实现以统一的方式被调用,这是适配器模式的体现。
java
public class SimpleControllerHandlerAdapter implements HandlerAdapter {
@Override
public boolean supports(Object handler) {
return (handler instanceof Controller);
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
return ((Controller) handler).handleRequest(request, response);
}
@Override
public long getLastModified(HttpServletRequest request, Object handler) {
return -1;
}
}