日期工具：非线程安全SimpleDateFormat 和线程安全JodaTime（推荐）-白红宇

日期工具：非线程安全SimpleDateFormat 和线程安全JodaTime（推荐）

阅读量：4219 次

发布时间：2019-05-26

本文共 4764 字，大约阅读时间需要 15 分钟。

1、SimpleDateFormat不是线程安全的对象

举个栗子：

@Slf4jpublic class DateFormatExample1 {        private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");    //  请求总数    public static int clientTotal = 5000;    // 同时并发执行的线程数    public static int threadTotal = 200;    public static StringBuffer stringBuffer = new StringBuffer();    public static void main(String[] args) throws InterruptedException {        ExecutorService executorService = Executors.newCachedThreadPool();        final Semaphore semaphore = new Semaphore(threadTotal);        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);        for (int i = 0; i< clientTotal; i ++) {            executorService.execute(()->{                try {                    semaphore.acquire();                    update();                    semaphore.release();                } catch (InterruptedException e) {                    e.printStackTrace();                }                countDownLatch.countDown();            });        }        countDownLatch.await();        executorService.shutdown();    }    public static void update() {        try {            simpleDateFormat.parse("20180208");        } catch (ParseException e) {            log.error("parse exception", e);        }    }    }

输出：

    at java.lang.Thread.run(Thread.java:748) 

    java.lang.NumberFormatException: multiple points 

    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890) 

    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110) 

    at java.lang.Double.parseDouble(Double.java:538) 

    at java.text.DigitList.getDouble(DigitList.java:169) 

    at java.text.DecimalFormat.parse(DecimalFormat.java:2056) 

    at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1867) 

    at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514) 

    at java.text.DateFormat.parse(DateFormat.java:364) 

    at com.example.concurrent.commonUnsafe.DateFormatExample1.update(DateFormatExample1.java:47) 

    at com.example.concurrent.commonUnsafe.DateFormatExample1.lambda$main$0(DateFormatExample1.java:33) 

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) 

    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) 

    at java.lang.Thread.run(Thread.java:748) 

2、改进上述SimpleDateFormat的用法（变为线程安全的）

改为局部变量（因为局部变量是堆栈封闭，线程安全的）每次声明一个新的变量来使用。

    如下： 

@Slf4jpublic class DateFormatExample2 {        //  请求总数    public static int clientTotal = 5000;    // 同时并发执行的线程数    public static int threadTotal = 200;    public static StringBuffer stringBuffer = new StringBuffer();    public static void main(String[] args) throws InterruptedException {        ExecutorService executorService = Executors.newCachedThreadPool();        final Semaphore semaphore = new Semaphore(threadTotal);        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);        for (int i = 0; i< clientTotal; i ++) {            executorService.execute(()->{                try {                    semaphore.acquire();                    update();                    semaphore.release();                } catch (InterruptedException e) {                    e.printStackTrace();                }                countDownLatch.countDown();            });        }        countDownLatch.await();        executorService.shutdown();    }    public static void update() {        try {            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");            simpleDateFormat.parse("20180208");        } catch (ParseException e) {            log.error("parse exception", e);        }    }}

3、利用JodaTime（线程安全的） （
推荐用这个，不关是因为线程安全的
）

    如下： 

@Slf4jpublic class DateFormatExample3 {    //  请求总数    public static int clientTotal = 5000;    // 同时并发执行的线程数    public static int threadTotal = 200;    private static DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd");    public static void main(String[] args) throws InterruptedException {        ExecutorService executorService = Executors.newCachedThreadPool();        final Semaphore semaphore = new Semaphore(threadTotal);        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);        for (int i = 0; i< clientTotal; i ++) {            final int count = i;            executorService.execute(()->{                try {                    semaphore.acquire();                    update(count);                    semaphore.release();                } catch (InterruptedException e) {                    e.printStackTrace();                }                countDownLatch.countDown();            });        }        countDownLatch.await();        executorService.shutdown();    }    public static void update(int i) {        log.info("{},{}", i, DateTime.parse("20180208").toDate());    }}

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