围绕外部库重写方法的AOP？

Question

我正在为以下问题寻找一个切实可行的解决方案：

• 外部库提供组件作为基类。
• 通过扩展这些基类生成自定义组件。
• 当实现引发未处理的异常时，基类将中断。
• 基类源代码不可用。只有二进制jar。

有人知道如何用AspectJ做这个吗？

Answer 1

假设外部库类/接口位于某个包中，如org.external.library或其任何子包中，您可以将这些类/接口用AspectJ语法表示为org.external.library..*+。..表示“包括子包”，*表示“所有类”，+表示“包括子类”。现在追加.*(..)，就可以获得所有方法，而不管这些类的名称和参数的数量如何。

现在，例如，切入点

execution(!static * org.external.library..*+.*(..))

拦截任何库子类中的所有非静态方法，而不考虑返回类型。

库类/接口：

package org.external.library;

public abstract class AbstractBase {
    public abstract String getText();
    public abstract int getNumber();
    public abstract void doSomething();
}

package org.external.library;

public interface Service {
    void start();
    void stop();
    boolean isRunning();
}

不扩展任何库类的类：

正如您所看到的，出于演示目的，该类在50%的情况下随机抛出运行时异常。我们希望它们不会被我们的方面处理。

package de.scrum_master.app;

import java.util.Random;

public class MyOwnClass {
    private static final Random RANDOM = new Random();

    public String getGreeting(String recipient) {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot get greeting for '" + recipient + "'");
        return "Hello " + recipient + "!";
    }
}

package de.scrum_master.app;

import java.util.Random;

import org.external.library.Service;

public class FooService implements Service {
    private static final Random RANDOM = new Random();
    private boolean isRunning;

    @Override
    public void start() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot start");
        isRunning = true;
    }

    @Override
    public void stop() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot stop");
        isRunning = false;
    }

    @Override
    public boolean isRunning() {
        return isRunning;
    }

    public void pause() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot pause");
        isRunning = false;
    }

    public void resume() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot resume");
        isRunning = true;
    }
}

package de.scrum_master.app;

import java.util.Random;

import org.external.library.AbstractBase;

public class Application extends AbstractBase {
    private static final Random RANDOM = new Random();

    @Override
    public String getText() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot get text");
        return "Hello world!";
    }

    @Override
    public int getNumber() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot get number");
        return RANDOM.nextInt(10);
    }

    @Override
    public void doSomething() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot do something");
    }

    public void doSomethingElse() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("cannot do something else");
    }

    public static void main(String[] args) {
        Application application = new Application();
        FooService fooService = new FooService();
        MyOwnClass myOwnClass = new MyOwnClass();
        for (int i = 0; i < 5; i++) {
            application.getText();
            application.getNumber();
            application.doSomething();
            application.doSomethingElse();
            fooService.start();
            fooService.pause();
            fooService.isRunning();
            fooService.resume();
            fooService.isRunning();
            fooService.stop();
            try {
                myOwnClass.getGreeting("world");
                myOwnClass.getGreeting("guys");
            }
            catch (Exception e) {
                System.out.println("Uncaught by aspect: " + e);
            }
        }
    }
}

package de.scrum_master.aspect;

public aspect ErrorHandler {
    Object around() : execution(!static * org.external.library..*+.*(..)) {
        try {
            return proceed();
        }
        catch (Exception e) {
            System.out.println(thisJoinPoint + " -> " + e);
            return null;
        }
    }
}

由于代码中的随机化，每次运行应用程序时，输出看起来都有点不同：

execution(int de.scrum_master.app.Application.getNumber()) -> java.lang.RuntimeException: cannot get number
execution(void de.scrum_master.app.Application.doSomething()) -> java.lang.RuntimeException: cannot do something
execution(void de.scrum_master.app.Application.doSomethingElse()) -> java.lang.RuntimeException: cannot do something else
execution(void de.scrum_master.app.FooService.start()) -> java.lang.RuntimeException: cannot start
execution(void de.scrum_master.app.FooService.pause()) -> java.lang.RuntimeException: cannot pause
execution(void de.scrum_master.app.FooService.resume()) -> java.lang.RuntimeException: cannot resume
execution(void de.scrum_master.app.FooService.stop()) -> java.lang.RuntimeException: cannot stop
Uncaught by aspect: java.lang.RuntimeException: cannot get greeting for 'world'
execution(String de.scrum_master.app.Application.getText()) -> java.lang.RuntimeException: cannot get text
execution(int de.scrum_master.app.Application.getNumber()) -> java.lang.RuntimeException: cannot get number
execution(void de.scrum_master.app.Application.doSomething()) -> java.lang.RuntimeException: cannot do something
execution(void de.scrum_master.app.FooService.start()) -> java.lang.RuntimeException: cannot start
execution(void de.scrum_master.app.FooService.pause()) -> java.lang.RuntimeException: cannot pause
execution(void de.scrum_master.app.FooService.stop()) -> java.lang.RuntimeException: cannot stop
Uncaught by aspect: java.lang.RuntimeException: cannot get greeting for 'guys'
execution(void de.scrum_master.app.Application.doSomething()) -> java.lang.RuntimeException: cannot do something
execution(void de.scrum_master.app.FooService.start()) -> java.lang.RuntimeException: cannot start
execution(void de.scrum_master.app.FooService.pause()) -> java.lang.RuntimeException: cannot pause
Uncaught by aspect: java.lang.RuntimeException: cannot get greeting for 'guys'
execution(void de.scrum_master.app.Application.doSomethingElse()) -> java.lang.RuntimeException: cannot do something else
execution(void de.scrum_master.app.FooService.resume()) -> java.lang.RuntimeException: cannot resume
execution(void de.scrum_master.app.FooService.stop()) -> java.lang.RuntimeException: cannot stop
Uncaught by aspect: java.lang.RuntimeException: cannot get greeting for 'world'
execution(String de.scrum_master.app.Application.getText()) -> java.lang.RuntimeException: cannot get text
execution(int de.scrum_master.app.Application.getNumber()) -> java.lang.RuntimeException: cannot get number
execution(void de.scrum_master.app.Application.doSomething()) -> java.lang.RuntimeException: cannot do something
execution(void de.scrum_master.app.Application.doSomethingElse()) -> java.lang.RuntimeException: cannot do something else
execution(void de.scrum_master.app.FooService.start()) -> java.lang.RuntimeException: cannot start
execution(void de.scrum_master.app.FooService.pause()) -> java.lang.RuntimeException: cannot pause
execution(void de.scrum_master.app.FooService.stop()) -> java.lang.RuntimeException: cannot stop