一、总结

1.1、使用System.currentTimeMillis();计算程序执行毫秒数

		// 开始时间1
		long startTime1 = System.currentTimeMillis();
		Thread.sleep(100);
		// 结束时间1
		long endTime1 = System.currentTimeMillis();

		// 开始时间2
		long startTime2 = System.currentTimeMillis();
		Thread.sleep(200);
		// 结束时间2
		long endTime2 = System.currentTimeMillis();
		System.out.println("逻辑1执行时间："+ (endTime1 - startTime1));
		System.out.println("逻辑2执行时间："+ (endTime2 -startTime2));

1.2、使用org.springframework.util包下的一个工具类StopWatch计算执行时间

		StopWatch testTask = new StopWatch("TestTask");
		// 记录开始时间点
		testTask.start("task1");
		Thread.sleep(100);
		// 记录结束时间点
		testTask.stop();
		// 记录开始时间点
		testTask.start("task2");
		Thread.sleep(200);
		// 记录结束时间点
		testTask.stop();
		// 输出执行时间
		System.out.println("==任务执行时间==");
		System.out.println(testTask.prettyPrint());
		System.out.println("执行任务的毫秒数："+testTask.getTotalTimeMillis());

1.3两个案例的完整代码、执行结果

package time.stopwatch;

import org.springframework.util.StopWatch;

public class StopWatchTest {
		public static void main(String[] args) throws InterruptedException {
		// 计算执行时间
		calculateExecuteTime1();
		// 计算执行时间
		calculateExecuteTime2();
	}

	public static void calculateExecuteTime1() throws InterruptedException {
		// 开始时间1
		long startTime1 = System.currentTimeMillis();
		Thread.sleep(100);
		// 结束时间1
		long endTime1 = System.currentTimeMillis();

		// 开始时间2
		long startTime2 = System.currentTimeMillis();
		Thread.sleep(200);
		// 结束时间2
		long endTime2 = System.currentTimeMillis();
		System.out.println("逻辑1执行时间："+ (endTime1 - startTime1));
		System.out.println("逻辑2执行时间："+ (endTime2 -startTime2));
	}

	public static void calculateExecuteTime2() throws InterruptedException {
		StopWatch testTask = new StopWatch("TestTask");
		// 记录开始时间点
		testTask.start("task1");
		Thread.sleep(100);
		// 记录结束时间点
		testTask.stop();
		// 记录开始时间点
		testTask.start("task2");
		Thread.sleep(200);
		// 记录结束时间点
		testTask.stop();
		// 输出执行时间
		System.out.println("==任务执行时间==");
		System.out.println(testTask.prettyPrint());
		System.out.println("执行任务的毫秒数："+testTask.getTotalTimeMillis());
	}
}

执行结果：

逻辑1执行时间：109
逻辑2执行时间：203
==任务执行时间==
StopWatch 'TestTask': running time = 319076700 ns
---------------------------------------------
ns         %     Task name
---------------------------------------------
114748000  036%  task1
204328700  064%  task2

执行任务的毫秒数：319

1.4 StopWatch优缺点：

优点：
1、spring自带工具类，可直接使用
2、代码实现简单，使用更简单
3、统一归纳，展示每项任务耗时与占用总时间的百分比，展示结果直观
4、性能消耗相对较小，并且最大程度的保证了start与stop之间的时间记录的准确性
5、可在start时直接指定任务名字，从而更加直观的显示记录结果
缺点：
1、一个StopWatch实例一次只能开启一个task，不能同时start多个task，并且在该task未stop之前不能start一个新的task，必须在该task stop之后才能开启新的task，若要一次开启多个，需要new不同的StopWatch实例
2、代码侵入式使用，需要改动多处代码

1.5、spring中StopWatch源码实现如下：

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('\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);
			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("\n");
			}
		}

		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;
		}
	}

}

原文摘录至：https://blog.csdn.net/gxs1688/article/details/87185030
致敬原作者：一个不二，侵删。