Java中的时间处理

时间：2022-05-18 23:49:33
  1. 日期时间组件使用

    java.util.Date：实现类，其对象具有时间、日期组件。
    java.util.Calendar：抽象类，其对象具有时间、日期组件。
    java.sql.Date：实现类，其对象具有日期组件。
    java.sql.Time：实现类，其对象具有时间组件。
    java.sql.Timestamp：实现类，其对象具有时间日期组件。
    java.text.DateFormat：抽象类，其对象格式化时间日期。
    java.text.DateFormatSymbols：实现类，其对象为格式化时间日期提供参数。

  2. long currentTime = System.currentTimeMillis(); //获取当前时间戳，从1970-01-01以来的毫秒数
            LOGGER.info("{}", currentTime);

            java.util.Date utilDate     = new java.util.Date(currentTime);
            LOGGER.info(    "{}|{}", utilDate, utilDate.getTime());

            Calendar calendar     = Calendar.getInstance(); //除某些特殊地区外，默认等效于new GregorianCalendar()
            calendar.setTimeInMillis(currentTime);
            LOGGER.info(    "{}", calendar);

            java.sql.Date sqlDate     = new java.sql.Date(currentTime);
            LOGGER.info(    "{}|{}", sqlDate, sqlDate.getTime());

            java.sql.Time sqlTime     = new java.sql.Time(currentTime);
            LOGGER.info(    "{}|{}", sqlTime, sqlTime.getTime());

            java.sql.Timestamp sqlTimestamp     = new java.sql.Timestamp(currentTime);
            LOGGER.info(    "{}|{}", sqlTimestamp, sqlTimestamp.getTime());

            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //默认是SimpleDateFormat
            LOGGER.info("{}", dateFormat.format(utilDate));
            LOGGER.info("{}", dateFormat.parse("2017-05-25 23:00:00"));

    输出：

    1495724884755 
    Thu May     25 23:08:04 CST 2017|1495724884755 
    java.util.GregorianCalendar[time    =1495724884755,...,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai"...] 
    2017-05-25|1495724884755 
    23:08:04|1495724884755 
    2017-05-25 23:08:04.755|1495724884755 
    2017-05-25 23:08:04 
    Thu May     25 23:00:00 CST 2017

  3. java.text.SimpleDateFormat的线程不安全问题
    问题重现：

            //final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");

            Callable    <Date> task = new Callable<Date>() {
                @Override
    public Date call() throws Exception {
                    LOGGER.info(    "executing task...");
    try{
    return new SimpleDateFormat("yyyy-MM-dd").parse("2017-05-25");
    //return format.parse("2017-05-25"); //if use shared SimpleDateFormat, executing result is not expected.
                    }catch (Exception ex){
                        LOGGER.error(    "Exception：", ex);
    return new Date(0);
                    }
                }
            };
    // pool with 5 threads
            ExecutorService exec = Executors.newFixedThreadPool(5);
            List    <Future<Date>> results = new ArrayList<Future<Date>>();
    // perform 10 date conversions
    for (int i = 0; i < 10; i++) {
                LOGGER.info(    "submit task[{}]", i);
                results.add(exec.submit(task));
            }
            exec.shutdown();
            LOGGER.info(    "shutdown");
    // look at the results
            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    for (Future<Date> result : results) {
                LOGGER.info(    "{}", dateFormat.format(result.get()));
            }
            LOGGER.info("completed");

    输出（使用共享的SimpleDateFormat时，执行结果并不是预期结果）：

    Java中的时间处理Java中的时间处理
    submit task[0] 
    submit task[    1] 
    submit task[    2] 
    executing task... 
    submit task[    3] 
    executing task... 
    submit task[    4] 
    executing task... 
    executing task... 
    submit task[    5] 
    executing task... 
    submit task[    6] 
    submit task[    7] 
    submit task[    8] 
    submit task[    9] 
    shutdown 
    executing task... 
    executing task... 
    executing task... 
    executing task... 
    executing task... 
    Exception： 
    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:    1869)
        at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:    1514)
        at java.text.DateFormat.parse(DateFormat.java:    364)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:65)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:59)
        at java.util.concurrent.FutureTask.run(FutureTask.java:    266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:    1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:    617)
        at java.lang.Thread.run(Thread.java:    745)
    Exception： 
    java.lang.NumberFormatException: empty String
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:    1842)
        at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:    110)
        at java.lang.Double.parseDouble(Double.java:    538)
        at java.text.DigitList.getDouble(DigitList.java:    169)
        at java.text.DecimalFormat.parse(DecimalFormat.java:    2056)
        at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:    1869)
        at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:    1514)
        at java.text.DateFormat.parse(DateFormat.java:    364)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:65)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:59)
        at java.util.concurrent.FutureTask.run(FutureTask.java:    266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:    1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:    617)
        at java.lang.Thread.run(Thread.java:    745)
    Exception： 
    java.lang.NumberFormatException: For input string:     "E.2505E2"
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:    2043)
        at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:    110)
        at java.lang.Double.parseDouble(Double.java:    538)
        at java.text.DigitList.getDouble(DigitList.java:    169)
        at java.text.DecimalFormat.parse(DecimalFormat.java:    2056)
        at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:    1869)
        at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:    1514)
        at java.text.DateFormat.parse(DateFormat.java:    364)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:65)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:59)
        at java.util.concurrent.FutureTask.run(FutureTask.java:    266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:    1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:    617)
        at java.lang.Thread.run(Thread.java:    745)
    Exception： 
    java.lang.NumberFormatException: For input string:     "E.2505"
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:    2043)
        at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:    110)
        at java.lang.Double.parseDouble(Double.java:    538)
        at java.text.DigitList.getDouble(DigitList.java:    169)
        at java.text.DecimalFormat.parse(DecimalFormat.java:    2056)
        at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:    1869)
        at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:    1514)
        at java.text.DateFormat.parse(DateFormat.java:    364)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:65)
        at com.liq.DateTimeTest$    1.call(DateTimeTest.java:59)
        at java.util.concurrent.FutureTask.run(FutureTask.java:    266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:    1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:    617)
        at java.lang.Thread.run(Thread.java:    745)
    1970-01-01 08:00:00 
    1970-01-01 08:00:00 
    1970-01-01 08:00:00 
    1970-01-01 08:00:00 
    2017-05-25 00:00:00 
    2017-05-25 00:00:00 
    2017-05-25 00:00:00 
    2017-05-25 00:00:00 
    2017-05-25 00:00:00 
    2017-05-25 00:00:00 
    completed
    View Code

    产生原因：
    SimpleDateFormat维护一个共享的Calendar对象，如果共享SimpleDateFomat时这个Calendar也是共享的。由多个线程并发进行操作就会有问题了。

    protected Calendar calendar;

    解决：
    （1）使用局部变量
    （2）使用 ThreadLocal

            final ThreadLocal<DateFormat> df = new ThreadLocal<DateFormat>() {
                @Override
    protected DateFormat initialValue() {
    return new SimpleDateFormat("yyyy-MM-dd");
                }
            };
    //final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");

            Callable    <Date> task = new Callable<Date>() {
                @Override
    public Date call() throws Exception {
                    LOGGER.info(    "executing task...");
    try{
    //return new SimpleDateFormat("yyyy-MM-dd").parse("2017-05-25");
    //return format.parse("2017-05-25"); //if use shared SimpleDateFormat, executing result is not expected.
    return df.get().parse("2017-05-25");
                    }    catch (Exception ex){
                        LOGGER.error(    "Exception：", ex);
    return new Date(0);
                    }
                }
            };

    （3）同步代码块 synchronized(code)
    （4）使用第三方的日期处理函数：比如使用 commons-lang 包中的 FastDateFormat 工具类

  4.  

参考：

  1. 如何在Java 8中愉快地处理日期和时间
  2. Java中的时间日期处理
  3. 详解SimpleDateFormat的线程安全问题与解决方案
  4. java中关于时间的处理 *
  5. 日历字段之间的转换
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