1 理论基础

1.1 AOP是什么

• 面向切面编程（AOP，Aspect Oriented Programming）

• 可以通过预编译方式和运行时动态代理，实现在不修改源代码的情况下，给程序动态增强功能的的一种技术

1.2 AOP能做什么

• 统计接口访问次数
• 数据库事务处理
• 增强功能：在不改动源代码的基础上，为接口增加一些额外的功能

2 Demo代码

2.1 引入依赖

<dependencies><dependency><groupId>org.springframework.bootgroupId><artifactId>spring-boot-starter-webartifactId>dependency><dependency><groupId>org.aspectjgroupId><artifactId>aspectjrtartifactId><version>1.9.4version>dependency><dependency><groupId>org.aspectjgroupId><artifactId>aspectjweaverartifactId><version>1.9.4version>dependency><dependency><groupId>cglibgroupId><artifactId>cglibartifactId><version>3.2.12version>dependency><dependency><groupId>com.alibabagroupId><artifactId>fastjsonartifactId><version>1.2.70version>dependency><dependency><groupId>org.springframework.bootgroupId><artifactId>spring-boot-starter-testartifactId><scope>testscope><exclusions><exclusion><groupId>org.junit.vintagegroupId><artifactId>junit-vintage-engineartifactId>exclusion>exclusions>dependency>dependencies>

2.2 API访问历史统计

/*** API访问历史统计*/
@Component
@Aspect
public class ApiVisitHistory {private Logger log = LoggerFactory.getLogger(ApiVisitHistory.class);private ThreadLocal<Long> startTime = new ThreadLocal<>();/*** 定义切面* - 此处代表com.smile.demo.controller包下的所有接口都会被统计*/@Pointcut("execution(* com.smile.demo.controller..*.*(..))")public void pointCut(){}/*** 在接口原有的方法执行前，将会首先执行此处的代码*/@Before("pointCut()")public void doBefore(JoinPoint joinPoint) {startTime.set(System.currentTimeMillis());//获取传入目标方法的参数Object[] args = joinPoint.getArgs();log.info("类名：{}", joinPoint.getSignature().getDeclaringType().getSimpleName());log.info("方法名:{}", joinPoint.getSignature().getName() );// 计数AtomicCounter.getInstance().increase();}/*** 只有正常返回才会执行此方法* 如果程序执行失败，则不执行此方法*/@AfterReturning(returning = "returnVal", pointcut = "pointCut()")public void doAfterReturning(JoinPoint joinPoint, Object returnVal) {HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();log.info("URI:[{}], 耗费时间:[{}] ms, 访问次数:{}", request.getRequestURI(), System.currentTimeMillis() - startTime.get(), AtomicCounter.getInstance().getValue());}/*** 当接口报错时执行此方法*/@AfterThrowing(pointcut = "pointCut()")public void doAfterThrowing(JoinPoint joinPoint) {HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();log.info("接口访问失败，URI:[{}], 耗费时间:[{}] ms", request.getRequestURI(), System.currentTimeMillis() - startTime.get());}
}

2.3 定义测试接口

@RestController
@RequestMapping("/demo/aop")
public class HelloController {@GetMapping("hello")public String hello() {return "hello World!";}
}

@RestController
@RequestMapping("/demo/aop")
public class ErrorController {@GetMapping("error")public String error() {int i = 1 / 0;return "测试报错的AOP方法";}
}

2.4 单例计数器

/*** 计数器，统计当前执行的任务数**/
public class AtomicCounter {private static final AtomicCounter atomicCounter = new AtomicCounter();/*** 单例，不允许外界主动实例化*/private AtomicCounter() { }public static AtomicCounter getInstance() {return atomicCounter;}private static AtomicInteger counter = new AtomicInteger();public int getValue() {return counter.get();}public int increase() {return counter.incrementAndGet();}public int decrease() {return counter.decrementAndGet();}}

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