Spring 中org.springframework.core.Ordered接口的实战教学

一、引言​

在 Spring 框架的生态系统中，众多组件需要协同工作。有时，我们希望某些组件按照特定的顺序执行，例如在拦截器链、事件监听器等场景下。org.springframework.core.Ordered接口应运而生，它提供了一种简单而有效的方式来定义组件的执行顺序。​

二、Ordered接口概述​

Ordered接口非常简洁，它只包含一个方法：

int getOrder();

该方法返回一个整数值，用于表示组件的顺序。值越小，优先级越高，执行顺序越靠前。Spring 框架中预定义了一些常用的顺序常量，例如：

public interface Ordered {int HIGHEST_PRECEDENCE = -2147483648;int LOWEST_PRECEDENCE = 2147483647;
}

三、实战场景一：自定义拦截器顺序​

假设我们有一个 Web 应用，需要定义多个拦截器，并且希望它们按照特定的顺序执行。​

（一）创建自定义拦截器​

首先，创建两个实现HandlerInterceptor接口的自定义拦截器，并实现Ordered接口。

自定义拦截器1：

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.core.Ordered;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class FirstInterceptor implements HandlerInterceptor, Ordered {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("FirstInterceptor preHandle");return true;}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("FirstInterceptor postHandle");}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("FirstInterceptor afterCompletion");}@Overridepublic int getOrder() {return 1;}
}

自定义拦截器2：

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.core.Ordered;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class SecondInterceptor implements HandlerInterceptor, Ordered {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("SecondInterceptor preHandle");return true;}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("SecondInterceptor postHandle");}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("SecondInterceptor afterCompletion");}@Overridepublic int getOrder() {return 2;}
}

（二）配置拦截器​

在 Spring 的配置类中注册并配置这两个拦截器。

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;@Configuration
public class WebMvcConfig implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new FirstInterceptor()).addPathPatterns("/**");registry.addInterceptor(new SecondInterceptor()).addPathPatterns("/**");}
}

当请求到达时，控制台输出结果如下：

FirstInterceptor preHandle
SecondInterceptor preHandle
SecondInterceptor postHandle
FirstInterceptor postHandle
SecondInterceptor afterCompletion
FirstInterceptor afterCompletion

可以看到，FirstInterceptor的preHandle方法先执行，因为它的getOrder()返回值更小，优先级更高。

四、实战场景二：事件监听器顺序​

Spring 的事件驱动模型中，也可以利用Ordered接口来控制事件监听器的执行顺序。​

（一）定义自定义事件

import org.springframework.context.ApplicationEvent;public class CustomEvent extends ApplicationEvent {public CustomEvent(Object source) {super(source);}
}

（二）创建事件监听器​

创建两个实现ApplicationListener接口的事件监听器，并实现Ordered接口。

事件监听器1：

import org.springframework.context.ApplicationListener;
import org.springframework.core.Ordered;public class FirstEventListener implements ApplicationListener<CustomEvent>, Ordered {@Overridepublic void onApplicationEvent(CustomEvent event) {System.out.println("FirstEventListener received event");}@Overridepublic int getOrder() {return 1;}
}

事件监听器2：

import org.springframework.context.ApplicationListener;
import org.springframework.core.Ordered;public class SecondEventListener implements ApplicationListener<CustomEvent>, Ordered {@Overridepublic void onApplicationEvent(CustomEvent event) {System.out.println("SecondEventListener received event");}@Overridepublic int getOrder() {return 2;}
}

（三）发布事件​

在某个服务类中发布自定义事件。

import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.stereotype.Service;@Service
public class EventPublisherService implements ApplicationEventPublisherAware {private ApplicationEventPublisher applicationEventPublisher;@Overridepublic void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {this.applicationEventPublisher = applicationEventPublisher;}public void publishCustomEvent() {CustomEvent customEvent = new CustomEvent(this);applicationEventPublisher.publishEvent(customEvent);}
}

当调用publishCustomEvent方法时，控制台输出结果如下：

FirstEventListener received event
SecondEventListener received event

再次验证了Ordered接口对执行顺序的控制。

五、总结​

通过上述两个实战场景，我们深入了解了org.springframework.core.Ordered接口在 Spring 框架中的应用。无论是自定义拦截器还是事件监听器，合理使用Ordered接口可以确保组件按照我们期望的顺序执行，从而提升系统的稳定性和可维护性。在实际项目中，根据业务需求灵活运用这一特性，将有助于构建更加健壮和高效的 Spring 应用。​