Code
2024-09-24 07:00:04

为什么Java的SimpleDateFormat不是线程安全的?

请用一个代码示例说明为什么SimpleDateFormat不是线程安全的。这门课的问题是什么? SimpleDateFormat的格式功能有问题吗? 请给出在课堂上演示此错误的代码。

FastDateFormat是线程安全的。为什么? SimpleDateFormat和FastDateFormat的区别是什么?

请用一个代码说明这个问题?

当前回答

下面这个例子会导致一个奇怪的错误。甚至谷歌也没有给出结果:

public class ExampleClass {

private static final Pattern dateCreateP = Pattern.compile("Дата подачи:\\s*(.+)");
private static final SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss dd.MM.yyyy");

public static void main(String[] args) {
    ExecutorService executor = Executors.newFixedThreadPool(100);
    while (true) {
        executor.submit(new Runnable() {
            @Override
            public void run() {
                workConcurrently();
            }
        });
    }
}

public static void workConcurrently() {
    Matcher matcher = dateCreateP.matcher("Дата подачи: 19:30:55 03.05.2015");
    Timestamp startAdvDate = null;
    try {
        if (matcher.find()) {
            String dateCreate = matcher.group(1);
            startAdvDate = new Timestamp(sdf.parse(dateCreate).getTime());
        }
    } catch (Throwable th) {
        th.printStackTrace();
    }
    System.out.print("OK ");
}
}

结果是:

OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK java.lang.NumberFormatException: For input string: ".201519E.2015192E2"
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.nonscalper.webscraper.processor.av.ExampleClass.workConcurrently(ExampleClass.java:37)
at com.nonscalper.webscraper.processor.av.ExampleClass$1.run(ExampleClass.java:25)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
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)
2015-05-27 19:49:24

其他回答

如果你想在多个线程中使用相同的日期格式，请将其声明为静态格式，并在使用时对实例变量进行同步…

static private SimpleDateFormat sdf = new SimpleDateFormat("....");

synchronized(sdf)
{
   // use the instance here to format a date
}


// The above makes it thread safe
2016-09-04 17:49:17

下面是一个代码示例，它证明了类中的错误。我检查过:问题发生在使用解析时，也当你只使用格式。

2013-02-06 17:58:15

ThreadLocal + SimpleDateFormat = SimpleDateFormatThreadSafe

package com.foocoders.text;

import java.text.AttributedCharacterIterator;
import java.text.DateFormatSymbols;
import java.text.FieldPosition;
import java.text.NumberFormat;
import java.text.ParseException;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

public class SimpleDateFormatThreadSafe extends SimpleDateFormat {

    private static final long serialVersionUID = 5448371898056188202L;
    ThreadLocal<SimpleDateFormat> localSimpleDateFormat;

    public SimpleDateFormatThreadSafe() {
        super();
        localSimpleDateFormat = new ThreadLocal<SimpleDateFormat>() {
            protected SimpleDateFormat initialValue() {
                return new SimpleDateFormat();
            }
        };
    }

    public SimpleDateFormatThreadSafe(final String pattern) {
        super(pattern);
        localSimpleDateFormat = new ThreadLocal<SimpleDateFormat>() {
            protected SimpleDateFormat initialValue() {
                return new SimpleDateFormat(pattern);
            }
        };
    }

    public SimpleDateFormatThreadSafe(final String pattern, final DateFormatSymbols formatSymbols) {
        super(pattern, formatSymbols);
        localSimpleDateFormat = new ThreadLocal<SimpleDateFormat>() {
            protected SimpleDateFormat initialValue() {
                return new SimpleDateFormat(pattern, formatSymbols);
            }
        };
    }

    public SimpleDateFormatThreadSafe(final String pattern, final Locale locale) {
        super(pattern, locale);
        localSimpleDateFormat = new ThreadLocal<SimpleDateFormat>() {
            protected SimpleDateFormat initialValue() {
                return new SimpleDateFormat(pattern, locale);
            }
        };
    }

    public Object parseObject(String source) throws ParseException {
        return localSimpleDateFormat.get().parseObject(source);
    }

    public String toString() {
        return localSimpleDateFormat.get().toString();
    }

    public Date parse(String source) throws ParseException {
        return localSimpleDateFormat.get().parse(source);
    }

    public Object parseObject(String source, ParsePosition pos) {
        return localSimpleDateFormat.get().parseObject(source, pos);
    }

    public void setCalendar(Calendar newCalendar) {
        localSimpleDateFormat.get().setCalendar(newCalendar);
    }

    public Calendar getCalendar() {
        return localSimpleDateFormat.get().getCalendar();
    }

    public void setNumberFormat(NumberFormat newNumberFormat) {
        localSimpleDateFormat.get().setNumberFormat(newNumberFormat);
    }

    public NumberFormat getNumberFormat() {
        return localSimpleDateFormat.get().getNumberFormat();
    }

    public void setTimeZone(TimeZone zone) {
        localSimpleDateFormat.get().setTimeZone(zone);
    }

    public TimeZone getTimeZone() {
        return localSimpleDateFormat.get().getTimeZone();
    }

    public void setLenient(boolean lenient) {
        localSimpleDateFormat.get().setLenient(lenient);
    }

    public boolean isLenient() {
        return localSimpleDateFormat.get().isLenient();
    }

    public void set2DigitYearStart(Date startDate) {
        localSimpleDateFormat.get().set2DigitYearStart(startDate);
    }

    public Date get2DigitYearStart() {
        return localSimpleDateFormat.get().get2DigitYearStart();
    }

    public StringBuffer format(Date date, StringBuffer toAppendTo, FieldPosition pos) {
        return localSimpleDateFormat.get().format(date, toAppendTo, pos);
    }

    public AttributedCharacterIterator formatToCharacterIterator(Object obj) {
        return localSimpleDateFormat.get().formatToCharacterIterator(obj);
    }

    public Date parse(String text, ParsePosition pos) {
        return localSimpleDateFormat.get().parse(text, pos);
    }

    public String toPattern() {
        return localSimpleDateFormat.get().toPattern();
    }

    public String toLocalizedPattern() {
        return localSimpleDateFormat.get().toLocalizedPattern();
    }

    public void applyPattern(String pattern) {
        localSimpleDateFormat.get().applyPattern(pattern);
    }

    public void applyLocalizedPattern(String pattern) {
        localSimpleDateFormat.get().applyLocalizedPattern(pattern);
    }

    public DateFormatSymbols getDateFormatSymbols() {
        return localSimpleDateFormat.get().getDateFormatSymbols();
    }

    public void setDateFormatSymbols(DateFormatSymbols newFormatSymbols) {
        localSimpleDateFormat.get().setDateFormatSymbols(newFormatSymbols);
    }

    public Object clone() {
        return localSimpleDateFormat.get().clone();
    }

    public int hashCode() {
        return localSimpleDateFormat.get().hashCode();
    }

    public boolean equals(Object obj) {
        return localSimpleDateFormat.get().equals(obj);
    }

}

https://gist.github.com/pablomoretti/9748230

2014-03-24 20:20:50

commons-lang的3.2版将拥有FastDateParser类，它是SimpleDateFormat的线程安全替代品。更多信息请参见LANG-909。

2013-08-08 09:08:39

下面这个例子会导致一个奇怪的错误。甚至谷歌也没有给出结果:

public class ExampleClass {

private static final Pattern dateCreateP = Pattern.compile("Дата подачи:\\s*(.+)");
private static final SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss dd.MM.yyyy");

public static void main(String[] args) {
    ExecutorService executor = Executors.newFixedThreadPool(100);
    while (true) {
        executor.submit(new Runnable() {
            @Override
            public void run() {
                workConcurrently();
            }
        });
    }
}

public static void workConcurrently() {
    Matcher matcher = dateCreateP.matcher("Дата подачи: 19:30:55 03.05.2015");
    Timestamp startAdvDate = null;
    try {
        if (matcher.find()) {
            String dateCreate = matcher.group(1);
            startAdvDate = new Timestamp(sdf.parse(dateCreate).getTime());
        }
    } catch (Throwable th) {
        th.printStackTrace();
    }
    System.out.print("OK ");
}
}

结果是:

OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK java.lang.NumberFormatException: For input string: ".201519E.2015192E2"
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.nonscalper.webscraper.processor.av.ExampleClass.workConcurrently(ExampleClass.java:37)
at com.nonscalper.webscraper.processor.av.ExampleClass$1.run(ExampleClass.java:25)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
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)
2015-05-27 19:49:24

推荐文章

aliyun

最新文章

标签

2024 code 京ICP备15047053号-1