一个简单的任务执行时间监视器 StopWatch

　有时我们在做开发的时候需要记录每个任务执行时间，或者记录一段代码执行时间，最简单的方法就是打印当前时间与执行完时间的差值，然后这样如果执行大量测试的话就很麻烦，并且不直观，

如果想对执行的时间做进一步控制，则需要在程序中很多地方修改，目前spring-framework提供了一个StopWatch类可以做类似任务执行时间控制，也就是封装了一个对开始时间，

结束时间记录操作的Java类，当然还有一些其他控制。源码如下：

/*
 * Copyright 2002-2010 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */  

package com.test;  

import java.text.NumberFormat;
import java.util.LinkedList;
import java.util.List;  

/**
 * Simple stop watch, allowing for timing of a number of tasks,
 * exposing total running time and running time for each named task.
 *
 * <p>Conceals use of <code>System.currentTimeMillis()</code>, improving the
 * readability of application code and reducing the likelihood of calculation errors.
 *
 * <p>Note that this object is not designed to be thread-safe and does not
 * use synchronization.
 *
 * <p>This class is normally used to verify performance during proof-of-concepts
 * and in development, rather than as part of production applications.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since May 2, 2001
 */
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<TaskInfo>();  

    /** Start time of the current task */
    private long startTimeMillis;  

    /** Is the stop watch currently running? */
    private boolean running;  

    /** Name of the current task */
    private String currentTaskName;  

    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.id = "";
    }  

    /**
     * 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;
    }  

    /**
     * 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.running) {
            throw new IllegalStateException("Can't start StopWatch: it's already running");
        }
        this.startTimeMillis = System.currentTimeMillis();
        this.running = true;
        this.currentTaskName = taskName;
    }  

    /**
     * Stop the current task. The results are undefined if timing
     * methods are called without invoking at least one pair
     * {@link #start()} / {@link #stop()} methods.
     * @see #start()
     */
    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);
        if (this.keepTaskList) {
            this.taskList.add(lastTaskInfo);
        }
        ++this.taskCount;
        this.running = false;
        this.currentTaskName = null;
    }  

    /**
     * Return whether the stop watch is currently running.
     */
    public boolean isRunning() {
        return this.running;
    }  

    /**
     * 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[this.taskList.size()]);
    }  

    /**
     * Return a short description of the total running time.
     */
    public String shortSummary() {
        return "StopWatch '" + this.id + "': 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()</code> 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;
        }
    }  

    /**
     * test
     * @throws InterruptedException
     */
    public static void main(String[] args) throws InterruptedException{
        StopWatch first = new StopWatch("First");
        first.start("A");
        Thread.sleep(200);
        first.stop();
        first.start("B");
        Thread.sleep(200);
        first.stop();
        first.start("C");
        Thread.sleep(120);
        first.stop();
        System.out.println(first.prettyPrint());  

    }
}  

执行结果如下：

1. StopWatch 'First': running time (millis) = 516
2. -----------------------------------------
3. ms     %     Task name
4. -----------------------------------------
5. 00203  039%  A
6. 00203  039%  B
7. 00110  021%  C

打印每个任务执行时间，以及占总时间百分比，个人开发测试时挺有用的，可以作为小工具收藏。