有時候要測試某個東東的執行效率，每次都得寫一堆 System.currentTimeMillis()，很顯然一般會封裝一下，避免重複造輪子，可以直接使用 Spring 提供的工具 StopWatch。其實在 Spring Boot 程序啓動後都會打印的啓動時間，也是基於這個類來的：
2020-04-25 17:09:41.468 INFO 60479 --- [ main] d.d.m.s.n.bootstrap.ConditionBootstrap : Started ConditionBootstrap in 1.006 seconds (JVM running for 1.688)
這個類應該是 Spring 最簡單的類之一了，代碼非常非常的簡單，沒有那些複雜的功能，適用於很簡單的場景。結合 start 和 stop 方法來看，對於單個 StopWatch 對象來說，只能開一個計時，任務執行完成後關閉計時，然後再開一個這樣操作，所以在多線程的環境下使用一定要注意，儘量避免 StopWatch 成爲公共變量。如果在多線程下有特殊需求，可以對 StopWatch 進行改造或者結合 ThreadLocal 來做。如果想做到無侵入性統計，可以基於 Java Agent 來做。
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.
*/
//唯一標識
private final String id;
//是否需要保存執行的任務
private boolean keepTaskList = true;
//記錄所有執行的任務
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;
//最近的任務
@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("");
}
...
/**
* 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()
*/
//開始任務
public void start(String taskName) throws IllegalStateException {
//不能連續開啓任務，只能開一個關一個
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()
*/
//結束任務，要注意這裏不能指定任務名稱，也就是說只能開一個關一個這樣去執行
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;
//將當前任務名稱置爲 null，所以判斷有沒有任務在執行可以根據這個參數是否爲null進行判斷
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.
*/
//打印任務信息，這裏會 format 成一個類似表格的統計信息
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.
*/
//任務類
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);
}
}
}
先看一個簡單的使用事例：
public class STDemo {
private static StopWatch sw = new StopWatch("20200425_Test");
private static ObjectMapper mapper = new ObjectMapper();
public static void main(String[] args) {
sw.start("task1");
sleep(1000);
printInfo();
sw.stop();
printInfo();
sw.start("task2");
printInfo();
sleep(2000);
sw.stop();
printInfo();
sw.start("task3");
sleep(3000);
printInfo();
sw.stop();
printInfo();
System.out.println(sw.prettyPrint());
}
private static void sleep(long millis) {
try {
Thread.sleep(millis);
} catch (InterruptedException ignored) {
}
}
private static void printInfo() {
//System.out.println("lastTaskInfo：" + sw.getLastTaskInfo());
Stream.of(sw.getTaskInfo()).forEach(a-> {
try {
System.out.println(mapper.writeValueAsString(a));
} catch (JsonProcessingException ignored) {
}
});
System.out.println("-----------------------");
}
}
歡迎關注公衆號
