Spring AOP 抛出后继续迭代

Question

我有MyClass 和AopLogger。如果doSomething 出现异常，则迭代停止。

如何防止退出logAround并继续下一个主机？而logAround返回的Object有什么用处，我们可以用这个Object做什么？

class MyClass{
    void check() throws Exception {    
        Iterator<Host> iter_host = configReader.getHostMap().values().iterator();       
        while (iter_host.hasNext()) {               
            Host host = (Host) iter_host.next();
            host.doSomething();
        }
    }
    void doSomething(){} //Exception 
}

class AopLogger {    
    @Around("execution(* com.mypackage..*.*(..))")
    Object logAround(ProceedingJoinPoint proceedingJoinPoint) throws Throwable{ 
        return proceedingJoinPoint.proceed();   
    } 
}

Answer 1

首先，你的切面类应该有一个@Aspect 注释。其次，如果你想使用 Spring AOP 而不是完整的 AspectJ，你的方面和所有目标类也应该是 Spring @Components。

话虽如此，这里有一个小样本。我是用普通的 AspectJ 创建的，但是 Spring AOP 中的切面代码应该是一样的。

帮助代码编译和运行的类：

package de.scrum_master.app;

import java.util.Random;

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

    private String name;

    public Host(String name) {
        this.name = name;
    }

    public void doSomething() {
        if (RANDOM.nextBoolean())
            throw new RuntimeException("oops!");
    }

    @Override
    public String toString() {
        return "Host(name=" + name + ")";
    }
}

package de.scrum_master.app;

import java.util.HashMap;
import java.util.Map;

public class ConfigReader {
    private Map<Integer, Host> hostMap = new HashMap<>();

    public ConfigReader() {
        hostMap.put(1, new Host("mercury"));
        hostMap.put(2, new Host("venus"));
        hostMap.put(3, new Host("earth"));
        hostMap.put(4, new Host("mars"));
    }

    public Map<Integer, Host> getHostMap() {
        return hostMap;
    }
}

驱动程序应用：

我不喜欢旧 JDK 版本遗留下来的 Iterator，因此我将其替换为更现代的 Java 风格 for 循环。

package de.scrum_master.app;

class MyClass {
    private ConfigReader configReader = new ConfigReader();

    void check() throws Exception {
        for (Host host : configReader.getHostMap().values()) {
            System.out.println(host);
            host.doSomething();
        }
    }

    public static void main(String[] args) throws Exception {
        new MyClass().check();
    }
}

切入点/建议方面同时进行日志记录和异常处理：

还请注意我在代码末尾的评论。

package de.scrum_master.aspect;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;

@Aspect
public class AopLogger {
    private static final InheritableThreadLocal<String> indent = new InheritableThreadLocal<String>() {
        @Override
        protected String initialValue() {
            return "";
        }
    };

    @Around("execution(* de.scrum_master.app..*(..)) && !execution(* toString())")
    public Object logAround(ProceedingJoinPoint thisJoinPoint) throws Throwable {
        Object result = null;
        System.out.println(indent.get() + ">> " + thisJoinPoint);
        try {
            indent.set(indent.get() + "  ");
            result = thisJoinPoint.proceed();
            indent.set(indent.get().substring(2));
        } catch (Exception e) {
            System.out.println(indent.get() + "Caught exception: " + e);
            indent.set(indent.get().substring(2));
        }
        System.out.println(indent.get() + "<< " + thisJoinPoint);

        // Attention: If a method with a caught exception does not have 'void'
        // return type, we return a (probably unexpected) result of 'null' here.
        // So maybe we should not catch all execptions but rather pick more
        // specific joinpoints where we are sure we can cleanly handle the
        // corresponding exceptions.
        return result;
    }
}

控制台日志：

>> execution(void de.scrum_master.app.MyClass.main(String[]))
  >> execution(void de.scrum_master.app.MyClass.check())
    >> execution(Map de.scrum_master.app.ConfigReader.getHostMap())
    << execution(Map de.scrum_master.app.ConfigReader.getHostMap())
Host(name=mercury)
    >> execution(void de.scrum_master.app.Host.doSomething())
      Caught exception: java.lang.RuntimeException: oops!
    << execution(void de.scrum_master.app.Host.doSomething())
Host(name=venus)
    >> execution(void de.scrum_master.app.Host.doSomething())
    << execution(void de.scrum_master.app.Host.doSomething())
Host(name=earth)
    >> execution(void de.scrum_master.app.Host.doSomething())
      Caught exception: java.lang.RuntimeException: oops!
    << execution(void de.scrum_master.app.Host.doSomething())
Host(name=mars)
    >> execution(void de.scrum_master.app.Host.doSomething())
      Caught exception: java.lang.RuntimeException: oops!
    << execution(void de.scrum_master.app.Host.doSomething())
  << execution(void de.scrum_master.app.MyClass.check())
<< execution(void de.scrum_master.app.MyClass.main(String[]))

将日志记录与异常处理分开的第二个方面变体：

package de.scrum_master.aspect;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;

@Aspect
public class AopLogger {
    private static final InheritableThreadLocal<String> indent = new InheritableThreadLocal<String>() {
        @Override
        protected String initialValue() {
            return "";
        }
    };

    @Around("execution(* de.scrum_master.app..*(..)) && !execution(* toString())")
    public Object logAround(ProceedingJoinPoint thisJoinPoint) throws Throwable {
        System.out.println(indent.get() + ">> " + thisJoinPoint);
        try {
            indent.set(indent.get() + "  ");
            Object result = thisJoinPoint.proceed();
            indent.set(indent.get().substring(2));
            System.out.println(indent.get() + "<< " + thisJoinPoint);
            return result;
        } catch (Exception e) {
            indent.set(indent.get().substring(2));
            System.out.println(indent.get() + "<< " + thisJoinPoint);
            throw e;
        }
    }

    @Around("execution(void de.scrum_master.app.Host.doSomething())")
    public void handleException(ProceedingJoinPoint thisJoinPoint) throws Throwable {
        try {
            thisJoinPoint.proceed();
        } catch (Exception e) {
            System.out.println(indent.get() + "Caught exception: " + e);
        }
    }
}

日志输出保持不变，但这次异常处理在一个单独的建议中，具有更精确的切入点。日志记录建议只处理日志记录（如果不是正确的缩进，它甚至不需要 try-catch）。异常处理建议只做自己的工作。

请随时提出后续问题。