优雅计时StopWatch

在程序中要对某一段业务逻辑进行计时，一般采用如下方法来统计耗时：

public static void main(String[] args) {
    long startTime = System.currentTimeMillis();
    doSomeThing();
    long endTime = System.currentTimeMillis();
    long totalTime = (endTime - startTime) / 1000;
    System.out.println("总共耗时：" + totalTime + "s");
}

private static void doSomeThing() {
    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

这种方式没毛病，还有一个工具类可以参考下，它叫StopWatch。使用方式介绍：

public static void main(String[] args) throws InterruptedException {
    StopWatch sw = new StopWatch();
    sw.start("A");
    Thread.sleep(500);
    sw.stop();
    sw.start("B");
    Thread.sleep(300);
    sw.stop();
    sw.start("C");
    Thread.sleep(200);
    sw.stop();
    System.out.println(sw.prettyPrint());
}

输出内容：

StopWatch '': running time (millis) = 1031
-----------------------------------------
ms     %     Task name
-----------------------------------------
00514  050%  A
00302  029%  B
00215  021%  C

注意：StopWatch要引SpringFramework的，不要引lang3的包。原理就是把StopWatch的start到stop这块代码计算好时间后，放到LinkedList中，当调用prettyPrint的时候，再格式化打印。在异步线程使用的时候，子线程一定要新new StopWatch()，否则统计不上。附上源码：

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

public void stop() throws IllegalStateException {
    if (this.currentTaskName == null) {
        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.currentTaskName = null;
    }
}