java - AOP围绕外部库的重写方法？

Question

我正在为以下问题寻找实用的解决方案:

• 外部库提供组件作为基类。
• 自定义组件是通过扩展这些基类制作的。
• 当实现抛出未处理的异常时，基类中断。
• 基类源代码不可用。只有一个二进制 jar。

我正在寻找的是有一个通用的 AOP 错误处理建议。它将包装每个方法的代码，这些方法是外部库中方法的直接覆盖或实现。基本上执行 try/catch 以进行错误恢复。

我当然可以手动搜索它们。然而，我们的代码库是广泛的。覆盖外部库类方法的可能性也是如此。因此考虑 AOP 来帮助我。

加载时编织被排除在外，因为它涉及到一个网络应用程序。可能无法使用应用程序服务器添加 JVM 代理程序。所以一定是编译时编织。

有人知道如何用 AspectJ 做到这一点吗？

Answer 1

假设您的外部库类/接口(interface)位于某个包中，例如 org.external.library 或其任何子包中，您可以用 AspectJ 语法将这些类/接口(interface)表示为 org.external.library..*+. .. 表示“包含子包”，* 表示“所有类”，+ 表示“包含子类”。现在附加 .*(..)，您将获得所有方法，而不管这些类的名称和参数数量。

现在以切入点为例

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

无论返回类型如何，拦截任何库子类中的所有非静态方法。

坏消息是您不能将切入点限制为覆盖方法，因为 @Override 注释具有保留类型“source”，即它不可用于方面匹配。但也许您只想将切入点缩小到公共(public)方法，以便排除内部方法抛出的错误。这取决于您的情况以及您想如何处理它。假设非重写方法也可以破坏基础组件，不过切入点很好。

这是一个自洽的样本:

库类/接口(interface):

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:

如您所见，出于演示目的，此类在约 50% 的所有情况下随机抛出运行时异常。我们希望它们不由我们的方面处理。

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 + "!";
    }
}

扩展/实现库类/接口(interface)的类:

如您所见，出于演示目的，这些类在大约 50% 的情况下还会随机抛出运行时异常。我们希望它们由我们的方面处理。

main 方法通过多次调用每个方法来演示整个设置，不处理重写库类中的任何错误，而只处理我们自己的类中的错误。

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);
            }
        }
    }
}

错误处理方面:

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;
        }
    }
}

控制台输出:

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些不同:

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