咱们常常须要统计一个办法的耗时，个别咱们会这样做：
public class Test { public static void main(String[] args) throws InterruptedException { long start = System.currentTimeMillis(); // 睡眠100ms，模仿工作耗时 Thread.sleep(100L); long end = System.currentTimeMillis(); System.out.println("耗时：" + (end - start)); // 输入 耗时：104 }}这样做尽管简略间接，当咱们须要分段统计耗时的时候，一不留神就找不到开始工夫在哪了。而且也不能汇总后果，不能直观的看到每一步的耗时。
有一个简略的小工具，能够帮忙咱们非常容易的统计办法耗时。
名字叫StopWatch，在常见的类库，例如Spring、Apache Commons、Google Guava都有这个工具，性能和实现都是大同小异，举荐应用Spring里的，能够更不便统计耗时的汇总后果。
把耗时代码换成StopWatch试一下：
public class Test { public static void main(String[] args) throws InterruptedException { // 创立统计工作 StopWatch stopWatch = new StopWatch(); // 开始计时 stopWatch.start(); // 睡眠100ms，模仿工作耗时 Thread.sleep(100L); // 完结计时 stopWatch.stop(); // 打印统计后果 System.out.println(stopWatch.prettyPrint()); }}输入后果是：
StopWatch '': running time (millis) = 104-----------------------------------------ms % Task name-----------------------------------------00104 100% 只统计了一个工作的耗时，还不能展现出StopWatch劣势，上面一次统计多个工作的耗时：
public class CopyTest { public static void main(String[] args) { // 创立统计工作，并指定ID StopWatch stopWatch = new StopWatch("Main办法耗时"); IntStream.rangeClosed(1, 10).forEach(index -> { // 开始计时，并指定工作名称，便于展现 stopWatch.start("task" + index); // 睡眠100ms，模仿工作耗时 try { Thread.sleep(100L); } catch (InterruptedException e) { } // 完结计时 stopWatch.stop(); }); // 打印统计后果 System.out.println(stopWatch.prettyPrint()); }}输入后果是：
StopWatch 'Main办法耗时': running time (millis) = 1039-----------------------------------------ms % Task name-----------------------------------------00103 010% task100107 010% task200104 010% task300104 010% task400105 010% task500102 010% task600104 010% task700102 010% task800105 010% task900103 010% task10打印出了每个工作的耗时，并统计了在总耗时所占百分比，曾经十分直观了。
这是怎么实现的呢？其实源码非常简单，就用一个LinkedList记录了每个工作的耗时：
public class StopWatch { // 总任务ID private final String id; // 工作汇合 private final List<TaskInfo> taskList = new LinkedList<TaskInfo>(); private long startTimeMillis; private boolean running; private String currentTaskName; private TaskInfo lastTaskInfo; private long totalTimeMillis; public StopWatch() { this(""); } public StopWatch(String id) { this.id = id; } public void start() throws IllegalStateException { start(""); } // 开始计时，并记录开始工夫 public void start(String taskName) throws IllegalStateException { if (this.running) { throw new IllegalStateException("Can't start StopWatch: it's already running"); } this.running = true; this.currentTaskName = taskName; this.startTimeMillis = System.currentTimeMillis(); } // 完结计时，统计耗时，并增加到taskList外面 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); this.taskList.add(lastTaskInfo); this.running = false; this.currentTaskName = null; } public long getLastTaskTimeMillis() throws IllegalStateException { if (this.lastTaskInfo == null) { throw new IllegalStateException("No tasks run: can't get last task interval"); } 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"); } return this.lastTaskInfo.getTaskName(); } public double getTotalTimeSeconds() { return this.totalTimeMillis / 1000.0; } public TaskInfo[] getTaskInfo() { return this.taskList.toArray(new TaskInfo[this.taskList.size()]); } public String shortSummary() { return "StopWatch '" + getId() + "': running time (millis) = " + getTotalTimeMillis(); } // 打印统计后果 public String prettyPrint() { StringBuilder sb = new StringBuilder(shortSummary()); sb.append('\n'); 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); for (TaskInfo task : getTaskInfo()) { sb.append(nf.format(task.getTimeMillis())).append(" "); sb.append(pf.format(task.getTimeSeconds() / getTotalTimeSeconds())).append(" "); sb.append(task.getTaskName()).append("\n"); } 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; } }}感觉怎么样？连忙应用起来吧。