StopWatch的使用
一、StopWatch介绍
简单的秒表，允许定时执行多个任务，公开总运行时间和每个命名任务的运行时间。 从而提高了应用程序代码的可读性并减少了计算错误的可能性。
请注意，此对象的设计不是线程安全的，并且不使用同步。 此类通常用于在概念验证和开发过程中验证性能，而不是作为生产应用程序的一部分。
从上面可以看得出来以下几点：
- 不是线程安全
- 用于验证开发过程的一些性能问题
- 有利于提高应用程序的可读性
二、使用示例
public class Main {
public static void main(String[] args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start("业务查询");
doSomething();
stopWatch.stop();
stopWatch.start("业务计算处理");
doSomething();
stopWatch.stop();
System.out.println(stopWatch.prettyPrint());
}
// 模拟业务处理的过程...
private static void doSomething() {
int time = Math.abs(new Random().nextInt(2000));
try {
Thread.sleep(time);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
打印的结果如下
StopWatch '': running time (millis) = 2067
-----------------------------------------
ms % Task name
-----------------------------------------
00830 040% 业务查询
01237 060% 业务计算处理
三、主要方法
- start()和start(taskName) 启动一个命名任务。如果在不调用此方法的情况下调用
#stop()或计时方法，则结果不确定(其实就是不打印)。 - stop() 停止当前任务。如果在不调用至少一对的情况下调用计时方法，则结果不确定。start()和stop()要成对出现。
- prettyPrint() 返回带有描述所有已执行任务的表的字符串。 对于自定义报告，请调用getTaskInfo（）并直接使用任务信息。
四、实现源码
public class StopWatch {
/**
* Identifier of this stop watch.
* Handy when we have output from multiple stop watches
* and need to distinguish between them in log or console output.
*/
private final String id;
private boolean keepTaskList = true;
private final List<TaskInfo> taskList = new LinkedList<>();
/** Start time of the current task. */
private long startTimeMillis;
/** Name of the current task. */
@Nullable
private String currentTaskName;
@Nullable
private TaskInfo lastTaskInfo;
private int taskCount;
/** Total running time. */
private long totalTimeMillis;
/**
* Construct a new stop watch. Does not start any task.
*/
public StopWatch() {
this("");
}
/**
* Construct a new stop watch with the given id.
* Does not start any task.
* @param id identifier for this stop watch.
* Handy when we have output from multiple stop watches
* and need to distinguish between them.
*/
public StopWatch(String id) {
this.id = id;
}
/**
* Return the id of this stop watch, as specified on construction.
* @return the id (empty String by default)
* @since 4.2.2
* @see #StopWatch(String)
*/
public String getId() {
return this.id;
}
/**
* Determine whether the TaskInfo array is built over time. Set this to
* "false" when using a StopWatch for millions of intervals, or the task
* info structure will consume excessive memory. Default is "true".
*/
public void setKeepTaskList(boolean keepTaskList) {
this.keepTaskList = keepTaskList;
}
/**
* Start an unnamed task. The results are undefined if {@link #stop()}
* or timing methods are called without invoking this method.
* @see #stop()
*/
public void start() throws IllegalStateException {
start("");
}
/**
* Start a named task. The results are undefined if {@link #stop()}
* or timing methods are called without invoking this method.
* @param taskName the name of the task to start
* @see #stop()
*/
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.startTimeMillis = System.currentTimeMillis();
}
/**
* Stop the current task. The results are undefined if timing
* methods are called without invoking at least one pair
* {@code start()} / {@code stop()} methods.
* @see #start()
*/
public void stop() throws IllegalStateException {
if (this.currentTaskName == null) {
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(this.lastTaskInfo);
}
++this.taskCount;
this.currentTaskName = null;
}
/**
* Return whether the stop watch is currently running.
* @see #currentTaskName()
*/
public boolean isRunning() {
return (this.currentTaskName != null);
}
/**
* Return the name of the currently running task, if any.
* @since 4.2.2
* @see #isRunning()
*/
@Nullable
public String currentTaskName() {
return this.currentTaskName;
}
/**
* Return the time taken by the last task.
*/
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();
}
/**
* Return the name of the last task.
*/
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();
}
/**
* Return the last task as a TaskInfo object.
*/
public TaskInfo getLastTaskInfo() throws IllegalStateException {
if (this.lastTaskInfo == null) {
throw new IllegalStateException("No tasks run: can't get last task info");
}
return this.lastTaskInfo;
}
/**
* Return the total time in milliseconds for all tasks.
*/
public long getTotalTimeMillis() {
return this.totalTimeMillis;
}
/**
* Return the total time in seconds for all tasks.
*/
public double getTotalTimeSeconds() {
return this.totalTimeMillis / 1000.0;
}
/**
* Return the number of tasks timed.
*/
public int getTaskCount() {
return this.taskCount;
}
/**
* 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[0]);
}
/**
* Return a short description of the total running time.
*/
public String shortSummary() {
return "StopWatch '" + getId() + "': running time (millis) = " + getTotalTimeMillis();
}
/**
* Return a string with a table describing all tasks performed.
* For custom reporting, call getTaskInfo() and use the task info directly.
*/
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("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();
}
/**
* Return an informative string describing all tasks performed
* For custom reporting, call {@code getTaskInfo()} and use the task info directly.
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder(shortSummary());
if (this.keepTaskList) {
for (TaskInfo task : getTaskInfo()) {
sb.append("; [").append(task.getTaskName()).append("] took ").append(task.getTimeMillis());
long percent = Math.round((100.0 * task.getTimeSeconds()) / getTotalTimeSeconds());
sb.append(" = ").append(percent).append("%");
}
}
else {
sb.append("; no task info kept");
}
return sb.toString();
}
/**
* Inner class to hold data about one task executed within the stop watch.
*/
public static final class TaskInfo {
private final String taskName;
private final long timeMillis;
TaskInfo(String taskName, long timeMillis) {
this.taskName = taskName;
this.timeMillis = timeMillis;
}
/**
* Return the name of this task.
*/
public String getTaskName() {
return this.taskName;
}
/**
* Return the time in milliseconds this task took.
*/
public long getTimeMillis() {
return this.timeMillis;
}
/**
* Return the time in seconds this task took.
*/
public double getTimeSeconds() {
return (this.timeMillis / 1000.0);
}
}
}
源码实现不难。
五、思考
- StopWatch通常用于日志的打印，可以简化我们手动进行日志输出的繁琐
- 让代码更专注业务逻辑而非日志输出
