您应该使用哪个 Java 类进行时间性能测量?
(可以使用任何日期/时间类,但我要问的原因是在.Net 中有一个为此目的指定的秒表类)
Spring 框架有一个优秀的StopWatch
类:
StopWatch stopWatch = new StopWatch("My Stop Watch");
stopWatch.start("initializing");
Thread.sleep(2000); // simulated work
stopWatch.stop();
stopWatch.start("processing");
Thread.sleep(5000); // simulated work
stopWatch.stop();
stopWatch.start("finalizing");
Thread.sleep(3000); // simulated work
stopWatch.stop();
System.out.println(stopWatch.prettyPrint());
这会产生:
秒表“我的秒表”:运行时间(毫秒)= 10000 ----------------------------------------- ms % 任务名称 ----------------------------------------- 02000 020% 初始化 05000 050% 处理 03000 030% 敲定
这是一个如何使用 StopWatch 通过注释专用方法来设置多个测量值的示例。非常有用且非常易于测量,例如多个嵌入式调用/操作上的服务调用等等。
秒表层次结构
package ch.vii.spring.aop;
import java.util.Arrays;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import org.springframework.util.StopWatch;
@Component
public class ProfilingMethodInterceptor implements MethodInterceptor {
private static final Logger log = LoggerFactory.getLogger(ProfilingMethodInterceptor.class);
public Object invoke(MethodInvocation invocation) throws Throwable {
if (log.isInfoEnabled()) {
String stopWatchName = invocation.getMethod().toGenericString();
StopWatchHierarchy stopWatch = StopWatchHierarchy.getStopWatchHierarchy(stopWatchName);
String taskName = invocation.getMethod().getName();
stopWatch.start(taskName);
try {
return invocation.proceed();
} finally {
stopWatch.stop();
}
} else {
return invocation.proceed();
}
}
static class StopWatchHierarchy {
private static final ThreadLocal<StopWatchHierarchy> stopwatchLocal = new ThreadLocal<StopWatchHierarchy>();
private static final IndentStack indentStack = new IndentStack();
static StopWatchHierarchy getStopWatchHierarchy(String id) {
StopWatchHierarchy stopWatch = stopwatchLocal.get();
if (stopWatch == null) {
stopWatch = new StopWatchHierarchy(id);
stopwatchLocal.set(stopWatch);
}
return stopWatch;
}
static void reset() {
stopwatchLocal.set(null);
}
final StopWatch stopWatch;
final Stack stack;
StopWatchHierarchy(String id) {
stopWatch = new StopWatch(id);
stack = new Stack();
}
void start(String taskName) {
if (stopWatch.isRunning()) {
stopWatch.stop();
}
taskName = indentStack.get(stack.size) + taskName;
stack.push(taskName);
stopWatch.start(taskName);
}
void stop() {
stopWatch.stop();
stack.pop();
if (stack.isEmpty()) {
log.info(stopWatch.prettyPrint());
StopWatchHierarchy.reset();
} else {
stopWatch.start(stack.get());
}
}
}
static class Stack {
private int size = 0;
String elements[];
public Stack() {
elements = new String[10];
}
public void push(String e) {
if (size == elements.length) {
ensureCapa();
}
elements[size++] = e;
}
public String pop() {
String e = elements[--size];
elements[size] = null;
return e;
}
public String get() {
return elements[size - 1];
}
public boolean isEmpty() {
return size == 0;
}
private void ensureCapa() {
int newSize = elements.length * 2;
elements = Arrays.copyOf(elements, newSize);
}
}
static class IndentStack {
String elements[] = new String[0];
public String get(int index) {
if (index >= elements.length) {
ensureCapa(index + 10);
}
return elements[index];
}
private void ensureCapa(int newSize) {
int oldSize = elements.length;
elements = Arrays.copyOf(elements, newSize);
for (int i = oldSize; i < elements.length; i++) {
elements[i] = new String(new char[i]).replace("\0", "| ");
}
}
}
}
顾问
package ch.vii.spring.aop;
import java.lang.reflect.Method;
import org.aopalliance.aop.Advice;
import org.springframework.aop.Pointcut;
import org.springframework.aop.support.AbstractPointcutAdvisor;
import org.springframework.aop.support.StaticMethodMatcherPointcut;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class ProfilingAdvisor extends AbstractPointcutAdvisor {
private static final long serialVersionUID = 1L;
private final StaticMethodMatcherPointcut pointcut = new StaticMethodMatcherPointcut() {
public boolean matches(Method method, Class<?> targetClass) {
return method.isAnnotationPresent(ProfileExecution.class);
}
};
@Autowired
private ProfilingMethodInterceptor interceptor;
public Pointcut getPointcut() {
return this.pointcut;
}
public Advice getAdvice() {
return this.interceptor;
}
}
ProfileExecution注解
package ch.vii.spring.aop;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Inherited
public @interface ProfileExecution {
}
注释您的代码
package ch.vii.spring;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import ch.vii.spring.aop.ProfileExecution;
@Component
public class Bean {
@Autowired
InnerBean innerBean;
@ProfileExecution
public void foo() {
innerBean.innerFoo();
innerBean.innerFoo2();
innerBean.innerFoo();
}
}
public class InnerBean {
@Autowired
InnerInnerBean innerInnerBean;
@ProfileExecution
public void innerFoo() {
}
@ProfileExecution
public void innerFoo2() {
innerInnerBean.innerInnerFoo();
innerInnerBean.innerInnerFoo();
innerInnerBean.innerInnerFoo();
}
}
输出
09:58:39.627 [main] INFO c.v.s.aop.ProfilingMethodInterceptor - StopWatch 'public void ch.vii.spring.Bean.foo()': running time (millis) = 215
-----------------------------------------
ms % Task name
-----------------------------------------
00018 008 % foo
00026 012 % | innerFoo
00001 000 % foo
00016 007 % | innerFoo2
00038 018 % | | innerInnerFoo
00000 000 % | innerFoo2
00024 011 % | | innerInnerFoo
00028 013 % | innerFoo2
00024 011 % | | innerInnerFoo
00029 013 % | innerFoo2
00000 000 % foo
00011 005 % | innerFoo
00000 000 % foo
System.nanoTime()
StopWatch
中提供的那个。查看 perf4j。Spring的秒表主要是为了本地开发。Perf4j 可以支持您的 POC 类型计时以及生产环境。
Performmetrics提供了一个方便的 Stopwatch 类。它可以测量挂钟时间等等:如果您需要更高的准确性,它还可以测量 CPU 时间、用户时间和系统时间。它很小,免费,您可以从 Maven Central 下载。更多信息和示例可以在这里找到:https ://obvj.net/performmetrics
Stopwatch sw = new Stopwatch();
sw.start();
// Your code here
sw.stop();
sw.printStatistics(System.out);
这会产生类似于以下内容的输出:
+-----------------+----------------------+--------------+
| Counter | Elapsed time | Time unit |
+-----------------+----------------------+--------------+
| Wall clock time | 85605718 | nanoseconds |
| CPU time | 78000500 | nanoseconds |
| User time | 62400400 | nanoseconds |
| System time | 15600100 | nanoseconds |
+-----------------+----------------------+--------------+
您只需传递自定义参数即可将指标转换为任何时间单位(纳秒、毫秒、秒等)。
PS:我是该工具的作者。
您可以尝试System.currentTimeMillis() ,但在一些知名 IDE 下也有很好的分析选项,例如 eclipse 和 netbeans。此外,远离 IDE,您可以在性能测量任务中尝试独立的分析器。我认为通过使用分析器,您将获得比使用System.currentTimeMillis()更好的结果。
如果您只想测量它,请使用秒表类,或者只是秒表。
如果你想让它更快,考虑这个。
最好的方法是使用 System.nanoTime(),但是,如果你想像 System.Diagnostics.Stopwatch 一样获得 Ticks(经过的 Ticks),那么你需要将纳秒转换为 Ticks(1 Tick = 100 纳秒),然后开始在nanos 和 millis, secs, mins, hours,然后最终将输出格式化为时间表示,例如 Elapsed() 方法之一(hh:mm:ss.sssssss),但是,Java 中的 Dates 仅使用 3 毫秒(hh:mm:ss.sss),因此您还需要锻炼格式。
我为 Java 做了一个秒表类,您可以从以下网址获取它:http ://carlosqt.blogspot.com/2011/05/stopwatch-class-for-java.html
例子:
package stopwatchapp;
import java.math.BigInteger;
public class StopwatchApp {
public static void main(String[] args) {
Stopwatch timer = new Stopwatch();
timer.start();
Fibonacci(40);
timer.stop();
System.out.println("Elapsed time in ticks: "
+ timer.getElapsedTicks());
System.out.println("Elapsed time in milliseconds: "
+ timer.getElapsedMilliseconds());
System.out.println("Elapsed time in seconds: "
+ timer.getElapsedSeconds());
System.out.println("Elapsed time in minutes: "
+ timer.getElapsedMinutes());
System.out.println("Elapsed time in hours: "
+ timer.getElapsedHours());
System.out.println("Elapsed time with format: "
+ timer.getElapsed());
}
private static BigInteger Fibonacci(int n)
{
if (n < 2)
return BigInteger.ONE;
else
return Fibonacci(n - 1).add(Fibonacci(n - 2));
}
}
输出:
// Elapsed time in ticks: 33432284
// Elapsed time in milliseconds: 3343
// Elapsed time in seconds: 3
// Elapsed time in minutes: 0
// Elapsed time in hours: 0
// Elapsed time with format: 00:00:03.3432284
希望这可以帮助。
如果您使用的是 JDK 9+,则可以使用 Flight Recorder。它具有极低的开销并使用不变的 TSC 进行计时,这比 System.nanoTime() 的侵入性要小
@StackTrace(false)
static class StopWatch extends Event {
int fib;
}
public static void main(String... args) throws IOException {
Recording r = new Recording();
r.start();
for (int i = 0; i < 500000; i++) {
StopWatch s = new StopWatch();
s.begin();
s.fib = fib(i%100);
s.commit();
}
r.stop();
Path p = Paths.get("recording.jfr");
r.dump(p);
for (RecordedEvent e : RecordingFile.readAllEvents(p)) {
System.out.println(e.getValue("fib") + " " + e.getDuration().toNanos() + " ns");
}
}
您也可以从命令行开始录制 (-XX:StartFlightRecording),然后在配置文件 (.jfc) 中启用事件(如果默认禁用它,@Enable(false))
这样,JIT 通常会优化 StopWatch 调用(转义分析、内联、死码消除等),因此您只有在想要测量某些东西时才需要付出代价。
private void WaitTimer(long ms)
{
long t = 0;
long x = System.currentTimeMillis();
while(t < ms)
{
t = System.currentTimeMillis() - x;
}
}