Spring AOP（二）@within() 和 @target
阿新 • • 發佈：2021-01-22
技術標籤：AOP&反射
如果多個類使用了多個註解，而且類之間有繼承關係，那AOP效果就熱鬧了！以下圖為例，Human類使用A1註解，Man類使用A2註解，Boy類沒有顯式使用註解。
形象比喻
@within() 和 @target的“作用域”有點像清朝的爵位和官位的“有效期”：
- @within() ，類似於爵位，是可以世襲的，老子跟著皇上出生入死，被分封的爵位兒子可以世襲，這叫封妻廕子。
- @target()，類似於官位，是不能世襲的，紈絝子弟，是不能讓他做官的。
@Before("@target(com.javatpoint.jjk.A1)")
public 上述程式碼可以形象地理解為，誰的官位是A1，就在他的所有方法執行前進行增強，即列印@target — A1，顯然，只有Human被封了官。這種官位是不能世襲的，所以，對Man和Boy無效。
@Before("@within(com.javatpoint.jjk.A2)") public void execute3() { System.out.println("@within --- A2"); }
上述程式碼可以形象地理解為，誰是A2爵位的受益者，就在他自己的方法，或者繼承的方法執行前增強，即列印@within — A2，顯然，Man、Boy都收益。Boy重寫的方法不會增強，這不是世襲的，也好理解！
完整程式碼
package com.javatpoint.jjk;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention package com.javatpoint.jjk;
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.TYPE)
public @interface A2 {
}
package com.javatpoint.jjk;
@A1
public class Human {
public void say(String sentence) {
System.out.println("Human says:" + sentence);
}
public void run() {
System.out.println("Human runs." );
}
public void jump() {
System.out.println("Human jump." );
}
}
package com.javatpoint.jjk;
@A2
public class Man extends Human{
@Override
public void run() {
System.out.println("Man runs." );
}
public void testMan() {
System.out.println("Man testMan." );
}
}
package com.javatpoint.jjk;
public class Boy extends Man {
@Override
public void jump() {
System.out.println("Boy jump." );
}
public void test() {
System.out.println("Bot test...");
}
}
package com.javatpoint.jjk;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;
@Aspect
@Component
public class HumanAspect
@Before("@within(com.javatpoint.jjk.A1)")
public void execute1() {
System.out.println("@within --- A1");
}
@Before("@target(com.javatpoint.jjk.A1)")
public void execute2() {
System.out.println("@target --- A1");
}
@Before("@within(com.javatpoint.jjk.A2)")
public void execute3() {
System.out.println("@within --- A2");
}
@Before("@target(com.javatpoint.jjk.A2)")
public void execute4() {
System.out.println("@target --- A2");
}
}
package com.javatpoint.jjk;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
@Configuration
@ComponentScan("com.javatpoint.jjk")
@EnableAspectJAutoProxy
public class HumanManager {
@Bean(name = "human")
public Human getHuman() {
return new Human();
}
@Bean(name = "man")
public Man getMan() {
return new Man();
}
@Bean(name = "boy")
public Boy getBoy() {
return new Boy();
}
}
package com.javatpoint;
import com.javatpoint.jjk.Boy;
import com.javatpoint.jjk.Human;
import com.javatpoint.jjk.HumanManager;
import com.javatpoint.jjk.Man;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.EnableAspectJAutoProxy;
@SpringBootApplication
@EnableAspectJAutoProxy(proxyTargetClass=true)
public class AopBeforeAdviceExampleApplication {
public static void main(String[] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(HumanManager.class);
Human human = context.getBean("human", Human.class);
System.out.println("---------------------This is a Human.");
human.say("hello!");
human.jump();
human.run();
Human man = context.getBean("man", Man.class);
System.out.println("---------------------This is a Man.");
man.say("hello!");
man.jump();
man.run();
Human boy = context.getBean("boy", Boy.class);
System.out.println("---------------------This is a Boy.");
boy.say("hello!");
boy.jump();
boy.run();
}
}
---------------------This is a Human.
@within --- A1
@target --- A1
Human says:hello!
@within --- A1
@target --- A1
Human jump.
@within --- A1
@target --- A1
Human runs.
---------------------This is a Man.
@within --- A1
@target --- A2
Human says:hello!
@within --- A1
@target --- A2
Human jump.
@within --- A2
@target --- A2
Man runs.
---------------------This is a Boy.
@within --- A1
Human says:hello!
Boy jump.
@within --- A2
Man runs.
資料
- https://blog.csdn.net/qq_36917119/article/details/108123440
- https://blog.csdn.net/demon7552003/article/details/97601209
- https://blog.csdn.net/yangshangwei/article/details/77846974