java工具類系列 （二.StopWatch）

 StopWatch 提供一個時間片記錄的API，該類是有apache下lang包中提供的，另外可以參考spring架構中的一個類似工具類，實現效果稍微不同，但都是提供一個時間記錄功能，見另一篇：http://blog.csdn.net/lxzo123/article/details/6608162

該工具類源碼如下：

/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements.  See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 org.apache.commons.lang3.time;/** * <p> * <code>StopWatch</code> provides a convenient API for timings. * </p> *  * <p> * To start the watch, call {@link #start()}. At this point you can: * </p> * <ul> * <li>{@link #split()} the watch to get the time whilst the watch continues in the background. {@link #unsplit()} will * remove the effect of the split. At this point, these three options are available again.</li> * <li>{@link #suspend()} the watch to pause it. {@link #resume()} allows the watch to continue. Any time between the * suspend and resume will not be counted in the total. At this point, these three options are available again.</li> * <li>{@link #stop()} the watch to complete the timing session.</li> * </ul> *  * <p> * It is intended that the output methods {@link #toString()} and {@link #getTime()} should only be called after stop, * split or suspend, however a suitable result will be returned at other points. * </p> *  * <p> * NOTE: As from v2.1, the methods protect against inappropriate calls. Thus you cannot now call stop before start, * resume before suspend or unsplit before split. * </p> *  * <p> * 1. split(), suspend(), or stop() cannot be invoked twice<br /> * 2. unsplit() may only be called if the watch has been split()<br /> * 3. resume() may only be called if the watch has been suspend()<br /> * 4. start() cannot be called twice without calling reset() * </p> *  * <p>This class is not thread-safe</p> *  * @since 2.0 * @version $Id: StopWatch.java 1088899 2011-04-05 05:31:27Z bayard $ */public class StopWatch {    private static final long NANO_2_MILLIS = 1000000L;    // running states    private static final int STATE_UNSTARTED = 0;    private static final int STATE_RUNNING = 1;    private static final int STATE_STOPPED = 2;    private static final int STATE_SUSPENDED = 3;    // split state    private static final int STATE_UNSPLIT = 10;    private static final int STATE_SPLIT = 11;    /**     * The current running state of the StopWatch.     */    private int runningState = STATE_UNSTARTED;    /**     * Whether the stopwatch has a split time recorded.     */    private int splitState = STATE_UNSPLIT;    /**     * The start time.     */    private long startTime;    /**     * The start time in Millis - nanoTime is only for elapsed time so we      * need to also store the currentTimeMillis to maintain the old      * getStartTime API.     */    private long startTimeMillis;    /**     * The stop time.     */    private long stopTime;    /**     * <p>     * Constructor.     * </p>     */    public StopWatch() {        super();    }    /**     * <p>     * Start the stopwatch.     * </p>     *      * <p>     * This method starts a new timing session, clearing any previous values.     * </p>     *      * @throws IllegalStateException     *             if the StopWatch is already running.     */    public void start() {        if (this.runningState == STATE_STOPPED) {            throw new IllegalStateException("Stopwatch must be reset before being restarted. ");        }        if (this.runningState != STATE_UNSTARTED) {            throw new IllegalStateException("Stopwatch already started. ");        }        this.startTime = System.nanoTime();        this.startTimeMillis = System.currentTimeMillis();        this.runningState = STATE_RUNNING;    }    /**     * <p>     * Stop the stopwatch.     * </p>     *      * <p>     * This method ends a new timing session, allowing the time to be retrieved.     * </p>     *      * @throws IllegalStateException     *             if the StopWatch is not running.     */    public void stop() {        if (this.runningState != STATE_RUNNING && this.runningState != STATE_SUSPENDED) {            throw new IllegalStateException("Stopwatch is not running. ");        }        if (this.runningState == STATE_RUNNING) {            this.stopTime = System.nanoTime();        }        this.runningState = STATE_STOPPED;    }    /**     * <p>     * Resets the stopwatch. Stops it if need be.     * </p>     *      * <p>     * This method clears the internal values to allow the object to be reused.     * </p>     */    public void reset() {        this.runningState = STATE_UNSTARTED;        this.splitState = STATE_UNSPLIT;    }    /**     * <p>     * Split the time.     * </p>     *      * <p>     * This method sets the stop time of the watch to allow a time to be extracted. The start time is unaffected,     * enabling {@link #unsplit()} to continue the timing from the original start point.     * </p>     *      * @throws IllegalStateException     *             if the StopWatch is not running.     */    public void split() {        if (this.runningState != STATE_RUNNING) {            throw new IllegalStateException("Stopwatch is not running. ");        }        this.stopTime = System.nanoTime();        this.splitState = STATE_SPLIT;    }    /**     * <p>     * Remove a split.     * </p>     *      * <p>     * This method clears the stop time. The start time is unaffected, enabling timing from the original start point to     * continue.     * </p>     *      * @throws IllegalStateException     *             if the StopWatch has not been split.     */    public void unsplit() {        if (this.splitState != STATE_SPLIT) {            throw new IllegalStateException("Stopwatch has not been split. ");        }        this.splitState = STATE_UNSPLIT;    }    /**     * <p>     * Suspend the stopwatch for later resumption.     * </p>     *      * <p>     * This method suspends the watch until it is resumed. The watch will not include time between the suspend and     * resume calls in the total time.     * </p>     *      * @throws IllegalStateException     *             if the StopWatch is not currently running.     */    public void suspend() {        if (this.runningState != STATE_RUNNING) {            throw new IllegalStateException("Stopwatch must be running to suspend. ");        }        this.stopTime = System.nanoTime();        this.runningState = STATE_SUSPENDED;    }    /**     * <p>     * Resume the stopwatch after a suspend.     * </p>     *      * <p>     * This method resumes the watch after it was suspended. The watch will not include time between the suspend and     * resume calls in the total time.     * </p>     *      * @throws IllegalStateException     *             if the StopWatch has not been suspended.     */    public void resume() {        if (this.runningState != STATE_SUSPENDED) {            throw new IllegalStateException("Stopwatch must be suspended to resume. ");        }        this.startTime += (System.nanoTime() - this.stopTime);        this.runningState = STATE_RUNNING;    }    /**     * <p>     * Get the time on the stopwatch.     * </p>     *      * <p>     * This is either the time between the start and the moment this method is called, or the amount of time between     * start and stop.     * </p>     *      * @return the time in milliseconds     */    public long getTime() {        return getNanoTime() / NANO_2_MILLIS;    }    /**     * <p>     * Get the time on the stopwatch in nanoseconds.     * </p>     *      * <p>     * This is either the time between the start and the moment this method is called, or the amount of time between     * start and stop.     * </p>     *      * @return the time in nanoseconds     * @since 3.0     */    public long getNanoTime() {        if (this.runningState == STATE_STOPPED || this.runningState == STATE_SUSPENDED) {            return this.stopTime - this.startTime;        } else if (this.runningState == STATE_UNSTARTED) {            return 0;        } else if (this.runningState == STATE_RUNNING) {            return System.nanoTime() - this.startTime;        }        throw new RuntimeException("Illegal running state has occured. ");    }    /**     * <p>     * Get the split time on the stopwatch.     * </p>     *      * <p>     * This is the time between start and latest split.     * </p>     *      * @return the split time in milliseconds     *      * @throws IllegalStateException     *             if the StopWatch has not yet been split.     * @since 2.1     */    public long getSplitTime() {        return getSplitNanoTime() / NANO_2_MILLIS;    }    /**     * <p>     * Get the split time on the stopwatch in nanoseconds.     * </p>     *      * <p>     * This is the time between start and latest split.     * </p>     *      * @return the split time in nanoseconds     *      * @throws IllegalStateException     *             if the StopWatch has not yet been split.     * @since 3.0     */    public long getSplitNanoTime() {        if (this.splitState != STATE_SPLIT) {            throw new IllegalStateException("Stopwatch must be split to get the split time. ");        }        return this.stopTime - this.startTime;    }    /**     * Returns the time this stopwatch was started.     *      * @return the time this stopwatch was started     * @throws IllegalStateException     *             if this StopWatch has not been started     * @since 2.4     */    public long getStartTime() {        if (this.runningState == STATE_UNSTARTED) {            throw new IllegalStateException("Stopwatch has not been started");        }        // System.nanoTime is for elapsed time        return this.startTimeMillis;    }    /**     * <p>     * Gets a summary of the time that the stopwatch recorded as a string.     * </p>     *      * <p>     * The format used is ISO8601-like, <i>hours</i>:<i>minutes</i>:<i>seconds</i>.<i>milliseconds</i>.     * </p>     *      * @return the time as a String     */    @Override    public String toString() {        return DurationFormatUtils.formatDurationHMS(getTime());    }    /**     * <p>     * Gets a summary of the split time that the stopwatch recorded as a string.     * </p>     *      * <p>     * The format used is ISO8601-like, <i>hours</i>:<i>minutes</i>:<i>seconds</i>.<i>milliseconds</i>.     * </p>     *      * @return the split time as a String     * @since 2.1     */    public String toSplitString() {        return DurationFormatUtils.formatDurationHMS(getSplitTime());    }}