怎么说呢，

编程方式？

如果想完整知道AOP的一些知识和使用场景还有坑。或者想在面试中拿到高分的，那也可以看下我写的这篇，内容相对比较完整的。好，我们开始吧，

至于横切关注点，AOP要解决什么问题

看一个典型的业务方法：

public void transfer {
// 权限检查
if ) {
throw new BusinessException;}
// 记录日志
log.info;// 事务管理
TransactionStatus status = txManager.getTransaction;try {
accountDao.deduct;其实，accountDao.increase;txManager.commit;} catch {
txManager.rollback;throw e，其实，}
log.info;}

整个方法里真正处理业务的只有两行：扣减转出方余额和增加转入方余额。权限检查、日志记录、事务管理占了绝大部分代码。

这些逻辑在支付方法、退款方法、充值方法里又各出现了一遍，代码几乎一样。

这类跟具体业务无关。但在每个业务方法里都要出现的逻辑，有个名字叫横切关注点。它们横跨在多个业务模块之上，不属于某一个特定的业务。话说回来，

抽取之后业务方法只剩主要原因：

@Transactional
public void transfer {
accountDao.deduct;accountDao.increase;}

用小区门卫理解代理机制

Spring AOP是基于代理实现的。理解了代理机制，后面所有的概念和问题都能自然串联起来。不过，

可以把Spring AOP想成小区门卫的模式。按理说，

• 住户 = 你写的Service类
• 门卫 = Spring在运行时生成的代理对象
• 外来访客通过门卫进小区 = 其他Bean调用你的方法时调到的是代理对象
• 门卫检查证件后放行 = @Before通知，目标方法执行前运行
• 门卫登记离开时间 = @After通知。 目标方法执行后运行
• 门卫拒绝来访者进入 = @Around通知，可以控制目标方法是否执行
• 多个门卫有值班顺序 = @Order注解控制多个切面的优先级

AOP实战这方面，两个高频场景

痛点一：接口耗时日志

每次手动添加日志太麻烦！如何自动记录所有接口调用情况？AOP提供一键方法，

AOP实战这块建议去读一下美团线上使用AOP进行日志实战文章 - 美团技术博客: - GitHub开源项目: 可以参考！

• Avoid manual logging in every method!
• Avoid missing important interface calls!
• Maintenance nightmare when requirements change!
• Auditing and debugging become extremely difficult!话说回来，
• The solution?按理说，A single annotation with AOP magic!

@Target
@Retention
public @interface ApiLog {
// 接口描述
String value default "";}
@Component
@Aspect
public class ApiLogAspect {
private static final Logger logger =
LoggerFactory.getLogger;@Around")
public Object around(ProceedingJoinPoint point,ApiLog apiLog) throws Throwable {
long startTime = System.currentTimeMillis;try {
Object result = point.proceed;logger.info(" {} executed successfully in {}ms"。apiLog.value,System.currentTimeMillis - startTime);return result;} catch {
logger.error(" {} failed after {}ms",apiLog.value。System.currentTimeMillis - startTime,e.getMessage);throw e，}
}
}

痛点二：接口权限校验

• "Anyone can access our APIs!" security alert!

@Target
@Retention
public @interface RequirePermission {
String value;}
@Component
@Aspect
public class PermissionAspect {
@Autowired
private PermissionService permissionService;@Before")
public void checkPermission(JoinPoint joinPoint,RequirePermission requirePermission) throws AccessDeniedException {
String userId = SecurityContextHolder.getContext
.getAuntication
.getName;if (，permissionService.hasPermission(userId,requirePermission.value)) {
throw new AccessDeniedException(
"User " + userId + " does not have permission for "
+ requirePermission.value);}
}
}

AOP vs Traditional Approaches Comparison
Maintaining Logs		Maintaining Permissions

Consiste nt loggi ng format s Centra lized co nfiguratio n Eas yto update an dmai ntai n Compre hensiv auditin gcapabilit es Minimizes huma nerro rs Enfor cesconsiste ncypractic esacros sdevelop ers Saves developme nt time a ndeffor t

Auto matic permi ssion check sbased o nan notati ons Redu cessecurit yrisks byenforci ngconsi ste ncyrules acros s entir esyst em Simplifie saudit ingand report ingprocesses Dynam icrole-based acces sc ontrol capabi litie s Minimizes huma nerro risallowi ngacciden talexpo sures ofsensiti ve data orfu nctionalit y Provides fine-grai nedcont rolove rapi operatio nsand data acces slevels  

JDK动态代理和CGLIB及与AspectJ区别表格说明如下:

// 生产环境容易遇到问题表格

CGLIB ProxyAspectJ tbodyclass'table-body' trclass'table-row' th scope='row'Implementation/th/ tddynamic proxy that implements specified interfaces/tddynamic subclass of proxied classtdbyte code weavingsupported at compile time or load-time/th/ /tr/

JDK Proxy

trclass'table-row' th scope='row'Performance/th/ tddirect interface invocation /tdmethod dispatch through generated subclass /tdenhanced performance as weaving happens once/th/ /tr/

trclass'table-row' th scope='row'Spring Integration/th/ tdexplicitly specify interfaces to proxy/tdautomatic support for any classtddirect support for any Java object without Spring container required/th/ /tr/>

trclass'table-row' th scope='row'API Limitations/th/ tdonly applicable if target implements interfaces/tdunderlying methods must be visible /tdnone - supports all types of methods including constructors and static methods/th/ /tr/>

trclass'table-row' th scope='row'Application Scope/th/ tdeffective only when accessed through interface reference/tdeffective regardless of how bean is accessed/tdenhanced objects behave as original objects everywhere including internal calls and static contexts/th/ /tr/>

trclass'table-row' th scope='row'Ease of Use/th/ tdeasy setup with minimal configuration/tdeasy setup with default CGLIB proxy creation/tdenhanced byte code requires AspectJ compiler or load-time agent configuration/th// /tr/

tbody//

table//

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