先看下这个问题的背景:假设有一个spring应用,开发人员希望自定义一个注解@Log,可以加到指定的方法上,实现自动记录日志(入参、出参、响应耗时这些)
package com.cnblogs.yjmyzz.springbootdemo.aspect; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface Log { }
然后再写一个Aspect来解析这个注解,对打了Log注解的方法进行增强处理
package com.cnblogs.yjmyzz.springbootdemo.aspect; import org.aspectj.lang.JoinPoint; import org.aspectj.lang.ProceedingJoinPoint; import org.aspectj.lang.annotation.Around; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Pointcut; import org.springframework.stereotype.Component; import java.lang.reflect.Method; @Component @Aspect public class LogAspect { @Pointcut("execution (* com.cnblogs.yjmyzz.springbootdemo.service..*.*(..))") public void logPointcut() { } @Around("logPointcut()") public void around(JoinPoint point) { String methodName = point.getSignature().getName(); Object[] args = point.getArgs(); Class<?>[] argTypes = new Class[point.getArgs().length]; for (int i = 0; i < args.length; i++) { argTypes[i] = args[i].getClass(); } Method method = null; try { method = point.getTarget().getClass().getMethod(methodName, argTypes); } catch (Exception e) { e.<p style="color:transparent">本文来源gao!%daima.com搞$代*!码$网3</p>printStackTrace(); } //获取方法上的注解 Log log = method.getAnnotation(Log.class); if (log != null) { //演示方法执行前,记录一行日志 System.out.println("before:" + methodName); } try { //执行方法 ((ProceedingJoinPoint) point).proceed(); } catch (Throwable throwable) { throwable.printStackTrace(); } finally { if (log != null) { //演示方法执行后,记录一行日志 System.out.println("after:" + methodName); } } } }
写一个测试Service类:
package com.cnblogs.yjmyzz.springbootdemo.service; import com.cnblogs.yjmyzz.springbootdemo.aspect.Log; import org.springframework.stereotype.Component; @Component public class HelloService { @Log public void sayHi(String msg) { System.out.println("\tsayHi:" + msg); } public void anotherSayHi(String msg) { this.sayHi(msg); } }
最后来跑一把:
package com.cnblogs.yjmyzz.springbootdemo; import com.cnblogs.yjmyzz.springbootdemo.service.HelloService; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.EnableAspectJAutoProxy; /** * @author 菩提树下的杨过 */ @ComponentScan("com.cnblogs.yjmyzz") @Configuration @EnableAspectJAutoProxy public class SampleApplication { public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SampleApplication.class); HelloService helloService = context.getBean(HelloService.class); helloService.sayHi("hi-1"); System.out.println("\n"); helloService.anotherSayHi("hi-2"); } }
输出如下:
显然HelloService中的anotherSayHi方法,并未被aop增强。 原因其实很简单,了解AOP原理的同学想必都知道,AOP的实现有二类,如果是基于接口的,会采用动态代理,生成一个代理类,如果是基于类的,会采用CGLib生成子类,然后在子类中扩展父类中的方法。