一：背景
Spring的AOP的存在目的是为了解耦。AOP可以让一组类共享相同的行为。在OOP中只能通过继承类和实现接口，来是代码的耦合度增强，且类继承只能为单继承，阻碍更多行为添加到一组类上，AOP弥补了OPP的不足。

二：概述 Spring支持AspectJ的注解方式切面编程

1.使用@Aspect 声明一个切面。

2.使用@After,@Before,@Around 定义建言（advice）,可直接将拦截规则（切点）作为参数。

3.其中@After,@Before,@Around参数的拦截规则为切点（PointCut） ,为了使切点复用，可使用@PointCut 专门定义拦截规则，然后在@After,@Before,@Around的参数中调用。

4.其中符合条件的每一个被拦截处为连接点（JoinPoint）

三：代码实例

1.pom.xml

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<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjrt</artifactId>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjweaver</artifactId>
</dependency>

2.拦截规则的注解

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@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Action {
String name();
}

2.注解的被拦截类

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@Service
public class DemoAnnotationService {
@Action(name = "注解式拦截的add操作")
public void add() {
System.out.println("======DemoAnnotationService方法add()=========");
}
}

3.方法规则被拦截类

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@Service
public class DemoMethodService {
public String add() throws Exception{
System.out.println("======DemoMethodService方法add()=========");
int i=100/0;
return "SUCCESS";
}
}

4.编写切面

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@Aspect
@Component
public class LogAspect {
@Pointcut("@annotation(com.gemdale.gmap.spring.boot.demo.Action)")
public void annotationPointCut() {
}
@After("annotationPointCut()")
public void after(JoinPoint joinPoint) {
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
Action action = method.getAnnotation(Action.class);
System.out.println("注解式拦截 " + action.name());
}
@Before("execution(* com.gemdale.gmap.spring.boot.demo.DemoMethodService.*(..))")
public void methodBefore(JoinPoint joinPoint) {
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
System.out.println("before方法规则式拦截 " + method.getName());
}
@After("execution(* com.gemdale.gmap.spring.boot.demo.DemoMethodService.*(..))")
public void methodAfter(JoinPoint joinPoint) {
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
System.out.println("after方法规则式拦截 " + method.getName());
}
@AfterReturning(pointcut = "execution(* com.gemdale.gmap.spring.boot.demo.DemoMethodService.*(..))", returning = "result")
public void methodAfterResult(JoinPoint joinPoint, Object result) {
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
System.out.println("after result方法规则式拦截 " + method.getName() + "result=" + result);
}
@AfterThrowing(pointcut = "execution(* com.gemdale.gmap.spring.boot.demo.DemoMethodService.*(..))", throwing = "e")
public void methodAfterException(JoinPoint joinPoint, Exception e) {
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
System.out.println("after exception方法规则式拦截 " + method.getName() + " e=" + e.getMessage());
}
}

5.配置类

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@Configuration
@ComponentScan("com.gemdale")
@EnableAspectJAutoProxy
public class AppliactionConfig {
}

6.执行类

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public class Start {
public static void main(String[] args) throws Exception{
AnnotationConfigApplicationContext configApplicationContext = new AnnotationConfigApplicationContext(
AppliactionConfig.class);
// UseFunctionService
// useFunctionService=configApplicationContext.getBean(UseFunctionService.class);
// System.out.println(useFunctionService.sayHello("Gengchong"));
DemoAnnotationService demoAnnotationService = configApplicationContext.getBean(DemoAnnotationService.class);
DemoMethodService demoMethodService = configApplicationContext.getBean(DemoMethodService.class);
demoAnnotationService.add();
demoMethodService.add();
configApplicationContext.close();
}
}

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Java 面向切面编程AOP

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