@target和@inner之间的区别（Spring AOP）

Question

任何连接点（仅在Spring AOP中执行方法），其中目标对象具有@transactional注释:@target(org.springframework.transaction.annotation.transactional)

任何连接点（仅在Spring AOP中执行方法），其中目标对象的声明类型具有@transactional注释:@inne(org.springframework.transaction.annotation.transactional)

但我看不出他们有什么不同！

所以我尝试添加带有类保留的自定义注释，但Spring抛出了一个异常（因为注释必须具有运行时保留）

Answer 1

您没有注意到任何区别，因为Spring AOP在使用AspectJ语法的同时，实际上只模拟了其功能的一个有限子集。因为Spring AOP是基于动态代理的，所以它只提供对公共的、非静态方法执行的拦截。（在使用CGLIB代理时，还可以截获包范围内的和受保护的方法。）然而，AspectJ还可以拦截方法调用（不仅仅是执行）、成员字段访问（静态和非静态）、构造函数调用/执行、静态类初始化等。

因此，让我们构造一个非常简单的AspectJ示例：

标记注释：

package de.scrum_master.app;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {}

package de.scrum_master.app;

@MyAnnotation
public class Application {
  private int nonStaticMember;
  private static int staticMember;

  public void doSomething() {
    System.out.println("Doing something");
    nonStaticMember = 11;
  }

  public void doSomethingElse() {
    System.out.println("Doing something else");
    staticMember = 22;
  }

  public static void main(String[] args) {
    Application application = new Application();
    application.doSomething();
    application.doSomethingElse();
  }
}

package de.scrum_master.aspect;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;

@Aspect
public class MyAspect {
  @Before("@within(de.scrum_master.app.MyAnnotation) && execution(public !static * *(..))")
  public void adviceAtWithin(JoinPoint thisJoinPoint) {
    System.out.println("[@within] " + thisJoinPoint);
  }

  @Before("@target(de.scrum_master.app.MyAnnotation) && execution(public !static * *(..))")
  public void adviceAtTarget(JoinPoint thisJoinPoint) {
    System.out.println("[@target] " + thisJoinPoint);
  }
}

[@within] execution(void de.scrum_master.app.Application.doSomething())
[@target] execution(void de.scrum_master.app.Application.doSomething())
Doing something
[@within] execution(void de.scrum_master.app.Application.doSomethingElse())
[@target] execution(void de.scrum_master.app.Application.doSomethingElse())
Doing something else

[@within] staticinitialization(de.scrum_master.app.Application.<clinit>)
[@within] execution(void de.scrum_master.app.Application.main(String[]))
[@within] call(de.scrum_master.app.Application())
[@within] preinitialization(de.scrum_master.app.Application())
[@within] initialization(de.scrum_master.app.Application())
[@target] initialization(de.scrum_master.app.Application())
[@within] execution(de.scrum_master.app.Application())
[@target] execution(de.scrum_master.app.Application())
[@within] call(void de.scrum_master.app.Application.doSomething())
[@target] call(void de.scrum_master.app.Application.doSomething())
[@within] execution(void de.scrum_master.app.Application.doSomething())
[@target] execution(void de.scrum_master.app.Application.doSomething())
[@within] get(PrintStream java.lang.System.out)
[@within] call(void java.io.PrintStream.println(String))
Doing something
[@within] set(int de.scrum_master.app.Application.nonStaticMember)
[@target] set(int de.scrum_master.app.Application.nonStaticMember)
[@within] call(void de.scrum_master.app.Application.doSomethingElse())
[@target] call(void de.scrum_master.app.Application.doSomethingElse())
[@within] execution(void de.scrum_master.app.Application.doSomethingElse())
[@target] execution(void de.scrum_master.app.Application.doSomethingElse())
[@within] get(PrintStream java.lang.System.out)
[@within] call(void java.io.PrintStream.println(String))
Doing something else
[@within] set(int de.scrum_master.app.Application.staticMember)

当只查看@target()时，我们会看到：

[@target] initialization(de.scrum_master.app.Application())
[@target] execution(de.scrum_master.app.Application())
[@target] call(void de.scrum_master.app.Application.doSomething())
[@target] execution(void de.scrum_master.app.Application.doSomething())
Doing something
[@target] set(int de.scrum_master.app.Application.nonStaticMember)
[@target] call(void de.scrum_master.app.Application.doSomethingElse())
[@target] execution(void de.scrum_master.app.Application.doSomethingElse())
Doing something else

对于每个方面输出行，我们还可以看到一个对应的@intern()匹配。现在让我们集中讨论哪些是不相同的，过滤输出的差异：

[@within] staticinitialization(de.scrum_master.app.Application.<clinit>)
[@within] execution(void de.scrum_master.app.Application.main(String[]))
[@within] call(de.scrum_master.app.Application())
[@within] preinitialization(de.scrum_master.app.Application())
[@within] get(PrintStream java.lang.System.out)
[@within] call(void java.io.PrintStream.println(String))
Doing something
[@within] get(PrintStream java.lang.System.out)
[@within] call(void java.io.PrintStream.println(String))
Doing something else
[@within] set(int de.scrum_master.app.Application.staticMember)

你看，在外表上

null