在 java 中编写自定义注释 - TimeCounter 注释示例 [英] Writing custom annotations in java - TimeCounter annotation example

问题描述

基本上，我需要使用自定义注释来跟踪在方法中花费的时间.(我知道spring AOP可以用于这个，但我们不能在我们的产品中使用它)

Basically I have a requirement to track time spent in a method using custom annotation. (I know spring AOP can be used for this, but we can not use it in our product).

public class TimeCounterDemo {
    
    @TimeCounter
    public void trackMyTimeSpentUsingAnnotation()
    {
        //some heavy processing stuff
    }   
}

public @interface TimeCounter {
  //need help with this implementation.
}

所以，我的要求是完成TimeCounter注解.要求很简单 -

So, my requirement is to complete the TimeCounter annotation. The requirement are simple -

1. 记录方法启动的时间.
2. 记录方法结束的时间.
3. 记录在方法中花费的总时间.
4. 执行的方法名称

有人可以帮助说明如何根据上述要求实现此注释.

Could someone help on how to implement this annotation to above requirements.

提前致谢.

推荐答案

已经有很多库提供了此类注释.如果您想要自己的实现，其中一种方法是使用 动态代理:

There are already many libraries that have such annotations available. If you want your own implementation, one of the appraoches would be to use dynamic proxies:

您的 TimeCounterDemo 可能如下所示:

Here's how your TimeCounterDemo may look like:

TimeCounter(注释)

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.METHOD)
public @interface TimeCounter {

}

ITimerCounterDemo(接口)

public interface ITimerCounterDemo {
    @TimeCounter
    public void trackMyTimeSpentUsingAnnotation();

    public void someOtherMethod(int a);
}

TimerCounterDemo(上面接口的实现)

public class TimerCounterDemo implements ITimerCounterDemo {
    
    public void trackMyTimeSpentUsingAnnotation() {
        System.out.println("TimerCounterDemo:: Going to sleep");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("TimerCounterDemo:: Completed.");
    }

    public void someOtherMethod(int a) {
        System.out.println("In someothermethod with value:: " + a);
    }
}

TimerProxy

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.time.Duration;
import java.time.LocalDateTime;
import java.util.Objects;

public class TimerProxy implements InvocationHandler {

    private Object targetObj;

    public static Object newInstance(Object targetObj) {
        Objects.requireNonNull(targetObj);
        return Proxy.newProxyInstance(
                      targetObj.getClass().getClassLoader(), 
                      targetObj.getClass().getInterfaces(),
                      new TimerProxy(targetObj)
               );
    }

    private TimerProxy(Object targetObj) {
        this.targetObj = targetObj;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.isAnnotationPresent(TimeCounter.class)) {

            LocalDateTime start = LocalDateTime.now();
            Object returnObj = method.invoke(targetObj, args);

            System.out.println(method.getName() + " executed in "
                    + Duration.between(start, LocalDateTime.now()).getSeconds() + " seconds");
            return returnObj;
        }

        return method.invoke(targetObj, args);
    }

}

测试计时器:

public class TimerTest {
    public static void main(String[] args) throws InterruptedException {
        ITimerCounterDemo t = (ITimerCounterDemo) TimerProxy.newInstance(new TimerCounterDemo());
        t.someOtherMethod(10);
        t.trackMyTimeSpentUsingAnnotation();
    }
}

输出:

In someothermethod with value:: 10
TimerCounterDemo:: Going to sleep
TimerCounterDemo:: Completed.
trackMyTimeSpentUsingAnnotation executed in 2 seconds

您可以在此处和这里

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