一个简单的任务执行时间监视器 StopWatch

有时我们在做开发的时候需要记录每个任务执行时间，或者记录一段代码执行时间，最简单的方法就是打印当前时间与执行完时间的差值，然后这样如果执行大量测试的话就很麻烦，并且不直观，如果想对执行的时间做进一步控制，则需要在程序中很多地方修改，目前spring-framework提供了一个StopWatch类可以做类似任务执行时间控制，也就是封装了一个对开始时间，结束时间记录操作的Java类，当然还有一些其他控制，代码如下：

/*
* Copyright 2002-2010 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0 *
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.test;

import java.text.NumberFormat;
import java.util.LinkedList;
import java.util.List;

/**
* Simple stop watch, allowing for timing of a number of tasks,
* exposing total running time and running time for each named task.
*
* <p>Conceals use of <code>System.currentTimeMillis()</code>, improving the
* readability of application code and reducing the likelihood of calculation errors.
*
* <p>Note that this object is not designed to be thread-safe and does not
* use synchronization.
*
* <p>This class is normally used to verify performance during proof-of-concepts
* and in development, rather than as part of production applications.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @author Sam Brannen
* @since May 2, 2001
*/
public class StopWatch {

/**
* Identifier of this stop watch.
* Handy when we have output from multiple stop watches
* and need to distinguish between them in log or console output.
*/
private final String id;

private boolean keepTaskList = true;

private final List<TaskInfo> taskList = new LinkedList<TaskInfo>();

/** Start time of the current task */
private long startTimeMillis;

/** Is the stop watch currently running? */
private boolean running;

/** Name of the current task */
private String currentTaskName;

private TaskInfo lastTaskInfo;

private int taskCount;

/** Total running time */
private long totalTimeMillis;

/**
* Construct a new stop watch. Does not start any task.
*/
public StopWatch() {
this.id = "";
}

/**
* Construct a new stop watch with the given id.
* Does not start any task.
* @param id identifier for this stop watch.
* Handy when we have output from multiple stop watches
* and need to distinguish between them.
*/
public StopWatch(String id) {
this.id = id;
}

/**
* Determine whether the TaskInfo array is built over time. Set this to
* "false" when using a StopWatch for millions of intervals, or the task
* info structure will consume excessive memory. Default is "true".
*/
public void setKeepTaskList(boolean keepTaskList) {
this.keepTaskList = keepTaskList;
}

/**
* Start an unnamed task. The results are undefined if {@link #stop()}
* or timing methods are called without invoking this method.
* @see #stop()
*/
public void start() throws IllegalStateException {
start("");
}

/**
* Start a named task. The results are undefined if {@link #stop()}
* or timing methods are called without invoking this method.
* @param taskName the name of the task to start
* @see #stop()
*/
public void start(String taskName) throws IllegalStateException {
if (this.running) {
throw new IllegalStateException("Can't start StopWatch: it's already running");
}
this.startTimeMillis = System.currentTimeMillis();
this.running = true;
this.currentTaskName = taskName;
}

/**
* Stop the current task. The results are undefined if timing
* methods are called without invoking at least one pair
* {@link #start()} / {@link #stop()} methods.
* @see #start()
*/
public void stop() throws IllegalStateException {
if (!this.running) {
throw new IllegalStateException("Can't stop StopWatch: it's not running");
}
long lastTime = System.currentTimeMillis() - this.startTimeMillis;
this.totalTimeMillis += lastTime;
this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
if (this.keepTaskList) {
this.taskList.add(lastTaskInfo);
}
++this.taskCount;
this.running = false;
this.currentTaskName = null;
}

/**
* Return whether the stop watch is currently running.
*/
public boolean isRunning() {
return this.running;
}

/**
* Return the time taken by the last task.
*/
public long getLastTaskTimeMillis() throws IllegalStateException {
if (this.lastTaskInfo == null) {
throw new IllegalStateException("No tasks run: can't get last task interval");
}
return this.lastTaskInfo.getTimeMillis();
}

/**
* Return the name of the last task.
*/
public String getLastTaskName() throws IllegalStateException {
if (this.lastTaskInfo == null) {
throw new IllegalStateException("No tasks run: can't get last task name");
}
return this.lastTaskInfo.getTaskName();
}

/**
* Return the last task as a TaskInfo object.
*/
public TaskInfo getLastTaskInfo() throws IllegalStateException {
if (this.lastTaskInfo == null) {
throw new IllegalStateException("No tasks run: can't get last task info");
}
return this.lastTaskInfo;
}

/**
* Return the total time in milliseconds for all tasks.
*/
public long getTotalTimeMillis() {
return this.totalTimeMillis;
}

/**
* Return the total time in seconds for all tasks.
*/
public double getTotalTimeSeconds() {
return this.totalTimeMillis / 1000.0;
}

/**
* Return the number of tasks timed.
*/
public int getTaskCount() {
return this.taskCount;
}

/**
* Return an array of the data for tasks performed.
*/
public TaskInfo[] getTaskInfo() {
if (!this.keepTaskList) {
throw new UnsupportedOperationException("Task info is not being kept!");
}
return this.taskList.toArray(new TaskInfo[this.taskList.size()]);
}

/**
* Return a short description of the total running time.
*/
public String shortSummary() {
return "StopWatch '" + this.id + "': running time (millis) = " + getTotalTimeMillis();
}

/**
* Return a string with a table describing all tasks performed.
* For custom reporting, call getTaskInfo() and use the task info directly.
*/
public String prettyPrint() {
StringBuilder sb = new StringBuilder(shortSummary());
sb.append('\n');
if (!this.keepTaskList) {
sb.append("No task info kept");
} else {
sb.append("-----------------------------------------\n");
sb.append("ms % Task name\n");
sb.append("-----------------------------------------\n");
NumberFormat nf = NumberFormat.getNumberInstance();
nf.setMinimumIntegerDigits(5);
nf.setGroupingUsed(false);
NumberFormat pf = NumberFormat.getPercentInstance();
pf.setMinimumIntegerDigits(3);
pf.setGroupingUsed(false);
for (TaskInfo task : getTaskInfo()) {
sb.append(nf.format(task.getTimeMillis())).append(" ");
sb.append(pf.format(task.getTimeSeconds() / getTotalTimeSeconds())).append(" ");
sb.append(task.getTaskName()).append("\n");
}
}
return sb.toString();
}

/**
* Return an informative string describing all tasks performed
* For custom reporting, call <code>getTaskInfo()</code> and use the task info directly.
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder(shortSummary());
if (this.keepTaskList) {
for (TaskInfo task : getTaskInfo()) {
sb.append("; [").append(task.getTaskName()).append("] took ").append(task.getTimeMillis());
long percent = Math.round((100.0 * task.getTimeSeconds()) / getTotalTimeSeconds());
sb.append(" = ").append(percent).append("%");
}
} else {
sb.append("; no task info kept");
}
return sb.toString();
}

/**
* Inner class to hold data about one task executed within the stop watch.
*/
public static final class TaskInfo {

private final String taskName;

private final long timeMillis;

TaskInfo(String taskName, long timeMillis) {
this.taskName = taskName;
this.timeMillis = timeMillis;
}

/**
* Return the name of this task.
*/
public String getTaskName() {
return this.taskName;
}

/**
* Return the time in milliseconds this task took.
*/
public long getTimeMillis() {
return this.timeMillis;
}

/**
* Return the time in seconds this task took.
*/
public double getTimeSeconds() {
return this.timeMillis / 1000.0;
}
}

/**
* test
* @throws InterruptedException
*/
public static void main(String[] args) throws InterruptedException{
StopWatch first = new StopWatch("First");
first.start("A");
Thread.sleep(200);
first.stop();
first.start("B");
Thread.sleep(200);
first.stop();
first.start("C");
Thread.sleep(120);
first.stop();
System.out.println(first.prettyPrint());

}
} 执行结果如下：
StopWatch 'First': running time (millis) = 516
-----------------------------------------
ms % Task name
-----------------------------------------
00203 039% A
00203 039% B
00110 021% C
打印每个任务执行时间，以及占总时间百分比，个人开发测试时挺有用的，可以作为小工具收藏。