blocks|key|923094|text|简单地说:你不能！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|923095|注释不是与代码一起自动启动的代码片段，它们只是注释，可以被其他处理代码的程序使用的信息片段，比如加载或运行代码。|923096|您需要的是AOP:面向方面的编程。|923097|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Simply put: you can't! 

Annotations are not pieces of code that get automatically started together with your code, they are just annotation, pieces of information that can be used by other programs working on your code like loading or running it.

What you need is AOP: aspect oriented programming.

blocks|key|923118|text|查看Coda+Hale+Metrics库。它为提供此功能的方法提供了@Timed注释。在此期间，请查看Code+Hale+Dropwizard，它提供了如何将其集成到其服务框架中的示例。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|923119|@GET
@Timed
public+Saying+sayHello(@QueryParam("name")+Optional<String>+name)+{
++++return+new+Saying(counter.incrementAndGet(),
++++++++++++++++++++++String.format(template,+name.or(defaultName)));
}|code-block|syntax|javascript|923120|entityMap|0|LINK|mutability|MUTABLE|url|http://metrics.codahale.com/|1|http://dropwizard.codahale.com/^0|2|H|0|1F|K|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

Check out the <a href="http://metrics.codahale.com/" rel="nofollow">Coda Hale Metrics</a> library. It provides a @Timed annotation for methods that provides this capability. While you're at it check out <a href="http://dropwizard.codahale.com/" rel="nofollow">Code Hale Dropwizard</a> which has examples for how its been integrated into their service framework.

<pre><code>@GET
@Timed
public Saying sayHello(@QueryParam("name") Optional&lt;String&gt; name) {
 return new Saying(counter.incrementAndGet(),
 String.format(template, name.or(defaultName)));
}
</code></pre>

blocks|key|706755|text|我对同样的事情想了好几次，最后写了下面的开头：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|706756|注释：|706757|package+main;
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+Clocking+{

}|code-block|syntax|javascript|706758|对象的接口：|706759|package+main;

public+interface+Examples+{
++++@Clocking
++++void+thisIsAMethod();

++++void+thisIsAnotherMethod(String+something);

++++@Clocking
++++void+thisIsALongRunningMethod();
}|706760|调用处理程序：|706761|package+main;
import+java.lang.reflect.InvocationHandler;
import+java.lang.reflect.Method;
import+java.time.Duration;
import+java.time.Instant;

public+class+ExamplesInvocationHandler+implements+InvocationHandler+{
++++//+******************************
++++//+Fields
++++//+******************************
++++private+Examples+examples+=+new+ExamplesImpl();

++++//+******************************
++++//+Public+methods
++++//+******************************
++++@Override
++++public+Object+invoke(Object+proxy,+Method+method,+Object[]+args)+throws+Throwable+{
++++++++//+If+the+annotation+is+not+present,+just+redirect+the+method+call+to+its+origin...
++++++++if(!method.isAnnotationPresent(Clocking.class))+{
++++++++++++return+method.invoke(examples,+args);
++++++++}

++++++++//+...+otherwise+log+the+execution+time+of+it.
++++++++Instant+start+=+Instant.now();
++++++++Object+returnObj+=+method.invoke(examples,+args);
++++++++Instant+end+=+Instant.now();

++++++++//+TODO:+This+is+for+demonstration+purpose+only+and+should+use+the+application's+logging+system.
++++++++System.out.println("Method+"+%2B+method.getName()+%2B+"+executed+in+"+%2B+Duration.between(end,+start)+%2B+".");

++++++++return+returnObj;
++++}

++++//+******************************
++++//+Inner+classes
++++//+******************************
++++private+static+class+ExamplesImpl+implements+Examples+{
++++++++@Override
++++++++public+void+thisIsAMethod()+{
++++++++++++System.out.println("thisIsAMethod+called!");
++++++++}

++++++++@Override
++++++++public+void+thisIsAnotherMethod(String+something)+{
++++++++++++System.out.println("thisIsAnotherMethod+called!");
++++++++}

++++++++@Override
++++++++public+void+thisIsALongRunningMethod()+{
++++++++++++try+{
++++++++++++++++Thread.sleep(5000);
++++++++++++}+catch+(InterruptedException+e)+{
++++++++++++++++e.printStackTrace();
++++++++++++}

++++++++++++System.out.println("thisIsALongRunningMethod+called!");
++++++++}
++++}
}|706762|最后一个入口点来测试这个：|706763|package+main;
import+java.lang.reflect.Proxy;

public+class+Main+{
++++public+static+void+main(String[]+args)+{
++++++++Examples+examples+=+(Examples)+Proxy.newProxyInstance(Examples.class.getClassLoader(),+new+Class[]{Examples.class},+new+ExamplesInvocationHandler());

++++++++examples.thisIsAMethod();
++++++++examples.thisIsAnotherMethod("");
++++++++examples.thisIsALongRunningMethod();
++++}
}|706764|这需要改进，因为它需要代理来实例化我们的对象，所以你不能真正将它用于“泛型已经编写”的代码。但它可能会让你找到更完整的东西。|706765|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

I wondered the same thing several time and ended by writting the following start:

The annotation:

<pre><code>package main;
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 Clocking {

}
</code></pre>

An object's interface:

<pre><code>package main;

public interface Examples {
 @Clocking
 void thisIsAMethod();

 void thisIsAnotherMethod(String something);

 @Clocking
 void thisIsALongRunningMethod();
}
</code></pre>

An invocation handler:

<pre><code>package main;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.time.Duration;
import java.time.Instant;

public class ExamplesInvocationHandler implements InvocationHandler {
 // ******************************
 // Fields
 // ******************************
 private Examples examples = new ExamplesImpl();

 // ******************************
 // Public methods
 // ******************************
 @Override
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
 // If the annotation is not present, just redirect the method call to its origin...
 if(!method.isAnnotationPresent(Clocking.class)) {
 return method.invoke(examples, args);
 }

 // ... otherwise log the execution time of it.
 Instant start = Instant.now();
 Object returnObj = method.invoke(examples, args);
 Instant end = Instant.now();

 // TODO: This is for demonstration purpose only and should use the application's logging system.
 System.out.println("Method " + method.getName() + " executed in " + Duration.between(end, start) + ".");

 return returnObj;
 }

 // ******************************
 // Inner classes
 // ******************************
 private static class ExamplesImpl implements Examples {
 @Override
 public void thisIsAMethod() {
 System.out.println("thisIsAMethod called!");
 }

 @Override
 public void thisIsAnotherMethod(String something) {
 System.out.println("thisIsAnotherMethod called!");
 }

 @Override
 public void thisIsALongRunningMethod() {
 try {
 Thread.sleep(5000);
 } catch (InterruptedException e) {
 e.printStackTrace();
 }

 System.out.println("thisIsALongRunningMethod called!");
 }
 }
}
</code></pre>

An finally an entry point to test this:

<pre><code>package main;
import java.lang.reflect.Proxy;

public class Main {
 public static void main(String[] args) {
 Examples examples = (Examples) Proxy.newProxyInstance(Examples.class.getClassLoader(), new Class[]{Examples.class}, new ExamplesInvocationHandler());

 examples.thisIsAMethod();
 examples.thisIsAnotherMethod("");
 examples.thisIsALongRunningMethod();
 }
}
</code></pre>

This needs an improvement, since it requires Proxy to instantiate our object and so you can't really use it for "generic already written" code.
But it might leads you to something more complete.

I want to write a java annotation which times the method call. something like this:

<pre><code>@TimeIt
public int someMethod() { ... }
</code></pre>

and when this method is invoked, it should output on console how long this method took

I know how to do it in python, this is what I want it to do:

<pre><code>from time import time, sleep

def time_it(func):
 def wrapper(*args, **kwargs):
 start = time()
 func(*args, **kwargs)
 stop = time()
 print "The function", func.__name__, " took %.3f" % (stop - start)
 wrapper.__name__ = func.__name__
 return wrapper

@time_it
def print_something(*args, **kwargs):
 print "before sleeping"
 print args, kwargs
 sleep(3) # wait 3 seconds
 print "after sleeping"

print_something(1, 2, 3, a="what is this?")
</code></pre>

So my questions are?
Where do I find some documentation to write something like this, I tried <a href="http://download.oracle.com/javase/1.5.0/docs/guide/apt/GettingStarted.html#AnnotationProcessor" rel="noreferrer"><code>apt</code></a> documentation, had no luck with it.
can someone help with writing something like this?

Writing a java annotation for timing method call

我想写一个java注解来计算方法调用的时间。如下所示：@TimeItpublic int someMethod() { ... }当调用此方法时，它应在控制台上输出此方法所用的时间我知道如何在python中做到这一点，这就是我想让它做的：from time import time, sleepdef time_it(f...

问编写用于计时方法调用的java注释
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