计时器StopWatch的使用（附完整源码）

因为经常用到，这里做下笔记，简单总结一下StopWatch的使用，Spring提供的计时器秒表支持方便以秒和毫秒为单位计时的程序时间特性的统计输出，尤其是单线程、顺序执行的程序。也就是说，如果我们有几个按顺序执行的任务，而我们又分别关心几个任务的执行所占用的时间，我们希望形成一个不那么复杂的日志输出，秒表提供了这样的功能。而Spring的秒表基本上只针对这个功能实现。

性急的朋友，先拿StopWatch测试源码：

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

public class StopWatch {
    private final String id;
    private boolean keepTaskList = true;
    private final List<TaskInfo> taskList = new LinkedList();
    private long startTimeMillis;
    private boolean running;
    private String currentTaskName;
    private StopWatch.TaskInfo lastTaskInfo;
    private int taskCount;
    private long totalTimeMillis;

    public StopWatch() {
        this.id = "";
    }

    public StopWatch(String id) {
        this.id = id;
    }

    public void setKeepTaskList(boolean keepTaskList) {
        this.keepTaskList = keepTaskList;
    }

    public void start() throws IllegalStateException {
        this.start("");
    }

    public void start(String taskName) throws IllegalStateException {
        if (this.running) {
            throw new IllegalStateException("Can't start StopWatch: it's already running");
        } else {
            this.startTimeMillis = System.currentTimeMillis();
            this.running = true;
            this.currentTaskName = taskName;
        }
    }

    public void stop() throws IllegalStateException {
        if (!this.running) {
            throw new IllegalStateException("Can't stop StopWatch: it's not running");
        } else {
            long lastTime = System.currentTimeMillis() - this.startTimeMillis;
            this.totalTimeMillis += lastTime;
            this.lastTaskInfo = new StopWatch.TaskInfo(this.currentTaskName, lastTime);
            if (this.keepTaskList) {
                this.taskList.add(this.lastTaskInfo);
            }

            ++this.taskCount;
            this.running = false;
            this.currentTaskName = null;
        }
    }

    public boolean isRunning() {
        return this.running;
    }

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

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

    public StopWatch.TaskInfo getLastTaskInfo() throws IllegalStateException {
        if (this.lastTaskInfo == null) {
            throw new IllegalStateException("No tasks run: can't get last task info");
        } else {
            return this.lastTaskInfo;
        }
    }

    public long getTotalTimeMillis() {
        return this.totalTimeMillis;
    }

    public double getTotalTimeSeconds() {
        return (double) this.totalTimeMillis / 1000.0D;
    }

    public int getTaskCount() {
        return this.taskCount;
    }

    public StopWatch.TaskInfo[] getTaskInfo() {
        if (!this.keepTaskList) {
            throw new UnsupportedOperationException("Task info is not being kept!");
        } else {
            return (StopWatch.TaskInfo[]) this.taskList.toArray(new StopWatch.TaskInfo[this.taskList.size()]);
        }
    }

    public String shortSummary() {
        return "StopWatch '" + this.id + "': running time (millis) = " + this.getTotalTimeMillis();
    }

    public String prettyPrint() {
        StringBuilder sb = new StringBuilder(this.shortSummary());
        sb.append('
');
        if (!this.keepTaskList) {
            sb.append("No task info kept");
        } else {
            sb.append("-----------------------------------------
");
            sb.append("ms     %     Task name
");
            sb.append("-----------------------------------------
");
            NumberFormat nf = NumberFormat.getNumberInstance();
            nf.setMinimumIntegerDigits(5);
            nf.setGroupingUsed(false);
            NumberFormat pf = NumberFormat.getPercentInstance();
            pf.setMinimumIntegerDigits(3);
            pf.setGroupingUsed(false);
            StopWatch.TaskInfo[] var7;
            int var6 = (var7 = this.getTaskInfo()).length;

            for (int var5 = 0; var5 < var6; ++var5) {
                StopWatch.TaskInfo task = var7[var5];
                sb.append(nf.format(task.getTimeMillis())).append("  ");
                sb.append(pf.format(task.getTimeSeconds() / this.getTotalTimeSeconds())).append("  ");
                sb.append(task.getTaskName()).append("
");
            }
        }

        return sb.toString();
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(this.shortSummary());
        if (this.keepTaskList) {
            StopWatch.TaskInfo[] var5;
            int var4 = (var5 = this.getTaskInfo()).length;

            for (int var3 = 0; var3 < var4; ++var3) {
                StopWatch.TaskInfo task = var5[var3];
                sb.append("; [").append(task.getTaskName()).append("] took ").append(task.getTimeMillis());
                long percent = Math.round(100.0D * task.getTimeSeconds() / this.getTotalTimeSeconds());
                sb.append(" = ").append(percent).append("%");
            }
        } else {
            sb.append("; no task info kept");
        }

        return sb.toString();
    }

    public static final class TaskInfo {
        private final String taskName;
        private final long timeMillis;

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

        public String getTaskName() {
            return this.taskName;
        }

        public long getTimeMillis() {
            return this.timeMillis;
        }

        public double getTimeSeconds() {
            return (double) this.timeMillis / 1000.0D;
        }
    }

}

　　感谢这几位大佬的文章：

唐磊(Jason) StopWatch方法详解

love_best stopWatch

BarryWang 计时器StopWatch的几种写法

Stopwatch 类
命名空间：System.Diagnostics.Stopwatch

实例化：Stopwatch getTime=new Stopwatch();

开始计时：getTime.Start();

getTime.Stop();

Console.WriteLine("getTime:"+totleTime .ElapsedMilliseconds.ToString ());

常用属性：Stopwatch.Elapsed 获取当前实例测量得出的总运行时间。

Stopwatch.ElapsedMilliseconds 获取当前实例测量得出的总运行时间（以毫秒计时）。

Stopwatch.ElapsedTicks 获取当前实例测量得出的总运行时间（用计时器计时周期表示）。