java中StopWatch的使用详解
作者：初夏0811
本文主要介绍了 java中StopWatch的使用详解，stopWatch使用它可直观的输出代码执行耗时，以及执行时间百分比，非常具有实用价值，需要的朋友可以参考下
stopWatch是org.springframework.util包下的一个工具类，使用它可直观的输出代码执行耗时，以及执行时间百分比，瞬间感觉比之前的方式高大上了一个档次。
在未使用这个工具类之前，如果我们需要统计某段代码的耗时，我们会这样写：
public static void main(String[] args) throws InterruptedException {
test0();
}
public static void test0() throws InterruptedException {
long start = System.currentTimeMillis();
// do something
Thread.sleep(100);
long end = System.currentTimeMillis();
long start2 = System.currentTimeMillis();
// do something
Thread.sleep(200);
long end2 = System.currentTimeMillis();
System.out.println("某某1执行耗时:" + (end - start));
System.out.println("某某2执行耗时:" + (end2 - start2));
}执行结果如下：
某某1执行耗时:100
某某2执行耗时:200
可以看出我们的代码比较繁琐，如果要统计更多的任务计时呢？更繁琐，甚至让代码显得有点low
下面来看一个stopWatch实现的一个示例：
public class StopWatchDemo {
public static void main(String[] args) throws InterruptedException {
test1();
}
public static void test1() throws InterruptedException {
StopWatch sw = new StopWatch("test");
sw.start("task1");
// do something
Thread.sleep(100);
sw.stop();
sw.start("task2");
// do something
Thread.sleep(200);
sw.stop();
System.out.println("sw.prettyPrint()~~~~~~~~~~~~~~~~~");
System.out.println(sw.prettyPrint());
}
}运行结果如下：
sw.prettyPrint()~~~~~~~~~~~~~~~~~
StopWatch 'test': running time (millis) = 310
-----------------------------------------
ms % Task name
-----------------------------------------
00110 035% task1
00200 065% task2
瞬间代码简介了，也高大上了，除此之外，还有以下两个方法shortSummary,getTotalTimeMillis，查看程序执行时间。
System.out.println("sw.shortSummary()~~~~~~~~~~~~~~~~~");
System.out.println(sw.shortSummary());
System.out.println("sw.getTotalTimeMillis()~~~~~~~~~~~~~~~~~");
System.out.println(sw.getTotalTimeMillis());运行结果
sw.shortSummary()~~~~~~~~~~~~~~~~~
StopWatch 'test': running time (millis) = 308
sw.getTotalTimeMillis()~~~~~~~~~~~~~~~~~
308
其实以上内容在该工具类中实现也极其简单，通过start与stop方法分别记录开始时间与结束时间，其中在记录结束时间时，会维护一个链表类型的tasklist属性，从而使该类可记录多个任务，最后的输出也仅仅是对之前记录的信息做了一个统一的归纳输出，从而使结果更加直观的展示出来。
我们来看下源码：
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;
}
}
}看源码就知道为何会打印如上那么高大上了。
最后来说下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，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；
4.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。
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