1.作用

用来记录任务的执行耗时
org.springframework.util.StopWatch
在org.springframework.boot.SpringApplication#run(java.lang.String…)中用到了计时器，用来计时spring 框架启动耗时

打印启动时间

private CharSequence getStartedMessage(StopWatch stopWatch) {
    StringBuilder message = new StringBuilder();
    message.append("Started ");
    appendApplicationName(message);
    message.append(" in ");
    message.append(stopWatch.getTotalTimeMillis() / 1000.0);
    message.append(" seconds");
    try {
        double uptime = ManagementFactory.getRuntimeMXBean().getUptime() / 1000.0;
        message.append(" (JVM running for ").append(uptime).append(")");
    }
    catch (Throwable ex) {
        // No JVM time available
    }
    return message;
}

在这里插入图片描述

2.计时器源码

构造函数

public StopWatch() {
    this("");
}

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

传入计时器的id，如果不传入则为空

开启计时器

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

主要设置当前任务的名称，并记录下当时的时间戳
System.nanoTime：返回的是时间的纳秒值，用来来做高精度的时间计算

停止计时器

public void stop() throws IllegalStateException {
    if (this.currentTaskName == null) {
        throw new IllegalStateException("Can't stop StopWatch: it's not running");
    }
    long lastTime = System.nanoTime() - this.startTimeNanos;
    this.totalTimeNanos += lastTime;
    this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
    if (this.keepTaskList) {
        this.taskList.add(this.lastTaskInfo);
    }
    ++this.taskCount;
    this.currentTaskName = null;
}

记录当前任务的用时，判断是否需要记录任务的明细，清空当前计时器

内部类：TaskInfo实现

public static final class TaskInfo {

    private final String taskName;

    private final long timeNanos;

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

打印结果：prettyPrint

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("ns         %     Task name\n");
        sb.append("---------------------------------------------\n");
        NumberFormat nf = NumberFormat.getNumberInstance();
        nf.setMinimumIntegerDigits(9);
        nf.setGroupingUsed(false);
        NumberFormat pf = NumberFormat.getPercentInstance();
        pf.setMinimumIntegerDigits(3);
        pf.setGroupingUsed(false);
        for (TaskInfo task : getTaskInfo()) {
            sb.append(nf.format(task.getTimeNanos())).append("  ");
            sb.append(pf.format((double) task.getTimeNanos() / getTotalTimeNanos())).append("  ");
            sb.append(task.getTaskName()).append("\n");
        }
    }
    return sb.toString();
}

3.计时器使用

StopWatch myWatch = new StopWatch("myWatch");
myWatch.start("test1");
Thread.sleep(1000L);
myWatch.stop();
myWatch.start("test2");
Thread.sleep(2000L);
myWatch.stop();
myWatch.start("test3");
Thread.sleep(8000L);
myWatch.stop();

System.out.println(myWatch.prettyPrint());

结果

StopWatch 'myWatch': running time = 11002394708 ns
---------------------------------------------
ns         %     Task name
---------------------------------------------
1002167975  009%  test1
2000082109  018%  test2
8000144624  073%  test3

原网址: 访问
创建于: 2023-02-16 12:00:02
目录: default
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