每天学习一点点之 Spring Web MVC 之抽象 HandlerInterceptor 实现常用功能（限流、权限等）

背景

这里介绍一下本文的背景（废话，可跳过）。上周有个我们服务的调用方反馈某个接口调用失败率很高，排查了一下，发现是因为这个接口被我之前写的一个限流器给拦截了，随着我们的服务接入了 Sentinel，这个限流器也可以下线了。于是今天又看了一下当初了实现，发现实现的很粗糙，核心还是基于 Spring AOP 实现的。

又突然想起前段时间由于某些原因想过下掉我们服务中使用的 Shiro，因为只是因为要使用 Shiro 的鉴权（ @RequiresPermissions）就要单独引入一个框架，有点重。感觉这种鉴权完全可以自己实现，那怎么实现呢，脑子第一印象又是 Spring AOP。

这里就陷入了一种误区，啥事都用 Spring AOP。Spring AOP 的实现会依赖动态代理，无论是使用 JDK 动态代理还是 CGLIB 动态代理，都会有一定的性能开销。但其实在 Web 端很多功能，都是可以避免使用 Spring AOP 减少无意义的性能损耗，比如上面提到的限流和鉴权。

抽象实现

其实原理很简单，就是基于 HandlerInterceptor 来做。但由于类似的功能会很多，比如限流、鉴权、日志打印等，可以将相关功能进行抽象，便于后续类似功能快速实现。

核心抽象类：

package blog.dongguabai.spring.web.mvc.handlerinterceptor.core;import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.util.Objects;/*** @author dongguabai* @date 2023-11-19 23:43*/
public abstract class CustomizedHandlerMethodInterceptor<A extends Annotation> implements HandlerInterceptor {private final Class<A> annotationType;protected CustomizedHandlerMethodInterceptor() {ParameterizedType superclass = (ParameterizedType) getClass().getGenericSuperclass();this.annotationType = (Class<A>) superclass.getActualTypeArguments()[0];}protected abstract boolean preHandle(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, A annotation) throws Exception;protected abstract void afterCompletion(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, A annotation, Exception ex) throws Exception;protected abstract void postHandle(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, ModelAndView modelAndView, A annotation) throws Exception;@Overridepublic final boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {if (handler instanceof HandlerMethod) {A annotation = getAnnotation((HandlerMethod) handler);if (match(annotation)) {return preHandle(request, response, (HandlerMethod) handler, annotation);}}return true;}@Overridepublic final void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {if (handler instanceof HandlerMethod) {A annotation = getAnnotation((HandlerMethod) handler);if (match(annotation)) {postHandle(request, response, (HandlerMethod) handler, modelAndView, annotation);}}}@Overridepublic final void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {if (handler instanceof HandlerMethod) {A annotation = getAnnotation((HandlerMethod) handler);if (match(annotation)) {afterCompletion(request, response, (HandlerMethod) handler, annotation, ex);}}}protected A getAnnotation(HandlerMethod handlerMethod) {return handlerMethod.getMethodAnnotation(annotationType);}protected boolean match(A annotation) {return Objects.nonNull(annotation);}}

接下来其他的业务功能只需要定义注解后，编写拦截器继承 CustomizedHandlerMethodInterceptor 即可。

业务快速实现：鉴权

定义注解：

package blog.dongguabai.spring.web.mvc.handlerinterceptor.require;import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** @author Dongguabai* @description* @date 2023-11-19 23:31*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
@Documented
public @interface RequiresPermissions {// PermissionsString[] value();
}

拦截器实现：

package blog.dongguabai.spring.web.mvc.handlerinterceptor.require;import blog.dongguabai.spring.web.mvc.handlerinterceptor.RequestContext;
import blog.dongguabai.spring.web.mvc.handlerinterceptor.core.CustomizedHandlerMethodInterceptor;
import org.springframework.stereotype.Component;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Arrays;
import java.util.List;/*** @author dongguabai* @date 2023-11-19 23:34*/
@Component
public class RequiresPermissionsHandlerMethodInterceptor extends CustomizedHandlerMethodInterceptor<RequiresPermissions> {@Overrideprotected boolean preHandle(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, RequiresPermissions annotation) throws Exception {List<String> permissons = Arrays.asList(annotation.value());if (RequestContext.getCurrentUser().getPermissions().stream().anyMatch(permissons::contains)){return true;}System.out.println("无权限.....");return false;}@Overrideprotected void afterCompletion(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, RequiresPermissions annotation, Exception ex) throws Exception {}@Overrideprotected void postHandle(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, ModelAndView modelAndView, RequiresPermissions annotation) throws Exception {}
}

也就是说标注了 RequiresPermissions 注解的接口都会进行鉴权。

验证一下：

package blog.dongguabai.spring.web.mvc.handlerinterceptor;import blog.dongguabai.spring.web.mvc.handlerinterceptor.require.RequiresPermissions;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;/*** @author dongguabai* @date 2023-11-20 00:17*/
@RestController
public class TestController {//只有拥有 BOSS 权限的用户才能调用@GetMapping("/get-reports")@RequiresPermissions("BOSS")public String getReports() {return "ALL...";}
}

模拟当前登陆用户（无 BOSS 权限）：

package blog.dongguabai.spring.web.mvc.handlerinterceptor;import java.util.Arrays;/*** @author dongguabai* @date 2023-11-20 01:21*/
public final class RequestContext {public static User getCurrentUser() {User user = new User();user.setUsername("tom");user.setPermissions(Arrays.asList("ADMIN", "STUDENT"));return user;}
}

调用：

➜  github curl http://localhost:8080/get-reports
{"message":"无权限..."}%

即拦截成功。

业务快速实现：限流

定义注解：

package blog.dongguabai.spring.web.mvc.handlerinterceptor.canyon;import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.concurrent.TimeUnit;/*** @author dongguabai* @date 2023-11-20 01:56*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
@Documented
public @interface Canyon {double value();long timeout() default 0;TimeUnit timeunit() default TimeUnit.SECONDS;String message() default "系统繁忙,请稍后再试.";
}

实现拦截器：

package blog.dongguabai.spring.web.mvc.handlerinterceptor.canyon;import blog.dongguabai.spring.web.mvc.handlerinterceptor.RequestContext;
import blog.dongguabai.spring.web.mvc.handlerinterceptor.core.CustomizedHandlerMethodInterceptor;
import blog.dongguabai.spring.web.mvc.handlerinterceptor.require.RequiresPermissions;
import org.springframework.stereotype.Component;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;
import java.util.Map;/*** @author dongguabai* @date 2023-11-19 23:34*/
@Component
public class CanyonHandlerMethodInterceptor extends CustomizedHandlerMethodInterceptor<Canyon> {@Overrideprotected boolean preHandle(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, Canyon annotation) throws Exception {if (tryAcquire()) {return true;}response.setContentType("application/json");response.setCharacterEncoding("UTF-8");response.getWriter().write(String.format("{\"message\":\"%s\"}", annotation.message()));return false;}@Overrideprotected void afterCompletion(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, Canyon annotation, Exception ex) throws Exception {}@Overrideprotected void postHandle(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod, ModelAndView modelAndView, Canyon annotation) throws Exception {}/*** todo:流量控制逻辑*/private boolean tryAcquire() {return false;}
}

验证一下：

package blog.dongguabai.spring.web.mvc.handlerinterceptor;import blog.dongguabai.spring.web.mvc.handlerinterceptor.canyon.Canyon;
import blog.dongguabai.spring.web.mvc.handlerinterceptor.require.RequiresPermissions;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;/*** @author dongguabai* @date 2023-11-20 00:17*/
@RestController
public class TestController {@GetMapping("/get-reports")@RequiresPermissions("BOSS")public String getReports() {return "ALL...";}@GetMapping("/search")@RequiresPermissions("ADMIN")@Canyon(1)public String search() {return "search...";}
}

调用：

➜  github curl http://localhost:8080/search     
{"message":"系统繁忙,请稍后再试."}%

即限流成功。

总结

本文首先阐述了虽然 Spring AOP 可以实现限流、鉴权等需要代理的功能，但由于依赖动态代理，会带来一定的性能损耗。然后通过对 HandlerInterceptor 的抽象，我们实现了一套在 Spring Web MVC 层面的静态代理机制，从而方便快速地在 Web 端实现代理功能。

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