非常好的代码。

http://www.rgagnon.com/javadetails/java-0585.html

import java.util.concurrent.TimeUnit;

long startTime = System.currentTimeMillis();
........
........
........
long finishTime = System.currentTimeMillis();

String diff = millisToShortDHMS(finishTime - startTime);


  /**
   * converts time (in milliseconds) to human-readable format
   *  "<dd:>hh:mm:ss"
   */
  public static String millisToShortDHMS(long duration) {
    String res = "";
    long days  = TimeUnit.MILLISECONDS.toDays(duration);
    long hours = TimeUnit.MILLISECONDS.toHours(duration)
                   - TimeUnit.DAYS.toHours(TimeUnit.MILLISECONDS.toDays(duration));
    long minutes = TimeUnit.MILLISECONDS.toMinutes(duration)
                     - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(duration));
    long seconds = TimeUnit.MILLISECONDS.toSeconds(duration)
                   - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(duration));
    if (days == 0) {
      res = String.format("%02d:%02d:%02d", hours, minutes, seconds);
    }
    else {
      res = String.format("%dd%02d:%02d:%02d", days, hours, minutes, seconds);
    }
    return res;
  }

对于java 8+，另一种可能的解决方案(更通用，函数风格，没有方面)可能是创建一些实用程序方法，将代码作为参数接受

public static <T> T timed (String description, Consumer<String> out, Supplier<T> code) {
    final LocalDateTime start = LocalDateTime.now ();
    T res = code.get ();
    final long execTime = Duration.between (start, LocalDateTime.now ()).toMillis ();
    out.accept (String.format ("%s: %d ms", description, execTime));
    return res;
}

调用代码可以是这样的smth:

public static void main (String[] args) throws InterruptedException {
    timed ("Simple example", System.out::println, Timing::myCode);
}

public static Object myCode () {
    try {
        Thread.sleep (1500);
    } catch (InterruptedException e) {
        e.printStackTrace ();
    }
    return null;
}

nanotime()是一个非常精确的系统实用程序，用于测量执行时间。但是要注意，如果运行在抢占式调度器模式(默认)，这个实用程序实际上测量的是时钟时间，而不是CPU时间。因此，您可能会注意到每次运行的执行时间值是不同的，这取决于系统负载。如果您需要CPU时间，我认为在实时模式下运行您的程序就可以了。您必须使用RT linux。链接:使用Linux进行实时编程

也可以实现定时器接口，并在类的任何方法上执行

import java.util.function.*;

public interface Timer {

    default void timeIt(Runnable r) {
        timeIt(() -> { r.run(); return 0;});
    }

    default <S,T> T timeIt(Function<S,T> fun, S arg) {
        long start = System.nanoTime();
        T result = fun.apply(arg);
        long stop = System.nanoTime();
        System.out.println("Time: " + (stop-start)/1000000.0 + " msec");
        return result;
    }

    default <T> T timeIt(Supplier<T> s) {
        return timeIt(obj -> s.get(), null);
    }
}

用法:

class MyClass implements Timer ..

timeIt(this::myFunction); 

为此，我们使用了AspectJ和Java注释。如果我们需要知道一个方法的执行时间，我们可以简单地注释它。更高级的版本可以使用自己的日志级别，可以在运行时启用和禁用。

public @interface Trace {
  boolean showParameters();
}

@Aspect
public class TraceAspect {
  [...]
  @Around("tracePointcut() && @annotation(trace) && !within(TraceAspect)")
  public Object traceAdvice ( ProceedingJintPoint jP, Trace trace ) {

    Object result;
    // initilize timer

    try { 
      result = jp.procced();
    } finally { 
      // calculate execution time 
    }

    return result;
  }
  [...]
}

非常好的代码。

http://www.rgagnon.com/javadetails/java-0585.html

import java.util.concurrent.TimeUnit;

long startTime = System.currentTimeMillis();
........
........
........
long finishTime = System.currentTimeMillis();

String diff = millisToShortDHMS(finishTime - startTime);


  /**
   * converts time (in milliseconds) to human-readable format
   *  "<dd:>hh:mm:ss"
   */
  public static String millisToShortDHMS(long duration) {
    String res = "";
    long days  = TimeUnit.MILLISECONDS.toDays(duration);
    long hours = TimeUnit.MILLISECONDS.toHours(duration)
                   - TimeUnit.DAYS.toHours(TimeUnit.MILLISECONDS.toDays(duration));
    long minutes = TimeUnit.MILLISECONDS.toMinutes(duration)
                     - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(duration));
    long seconds = TimeUnit.MILLISECONDS.toSeconds(duration)
                   - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(duration));
    if (days == 0) {
      res = String.format("%02d:%02d:%02d", hours, minutes, seconds);
    }
    else {
      res = String.format("%dd%02d:%02d:%02d", days, hours, minutes, seconds);
    }
    return res;
  }