StopWatch的用法

在學習spring的時候，看到關於統計時間的類，比較好奇，就記錄下來，以便以后用到可以直接使用
org.springframework.util.StopWatch
StopWatch該類在統計時間的時候，必須得前一個對象關閉才能創建新的StopWatch，並且在統計完成后，只需要將其輸出，就可以像報表一樣，顯示統計的時間
在開發中，常用於統計時間的是 使用 System.currentTimeMillis();進行統計，並且當執行完畢后，
還需要相減，才能得到最終時間值，不過，stopWatch差不多也是類似功能吧

	public static void main(String[] args) throws InterruptedException {
		StopWatch sw = new StopWatch();
		sw.start("讀取文件");
		Thread.sleep(1000);
		sw.stop();
		sw.start("文件刪除");
		Thread.sleep(100);
		sw.stop();
		sw.start("文件拷貝");
		Thread.sleep(10);
		sw.stop();
		System.out.println(sw.prettyPrint());
		
		long stime =System.currentTimeMillis();
		Thread.sleep(1000);
		long etime =System.currentTimeMillis();
		System.out.println("執行時間:"+(etime-stime));
	}

 

執行結果：
StopWatch '': running time (millis) = 1110
-----------------------------------------
ms % Task name
-----------------------------------------
01000 090% 讀取文件
00100 009% 文件刪除
00010 001% 文件拷貝

執行時間:1000

 查看其內部源碼，我們可以看到，該類封裝了System.currentTimeMillis();在同一個stopWatch對象中，將每次stop都存放在linklist中，在統計的時候，再取出輸出

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

	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 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()]);
	}