Java Review - SimpleDateFormat线程不安全原因的源码分析及解决办法
【摘要】
文章目录
概述复现问题源码分析
概述
SimpleDateFormat是Java提供的一个格式化和解析日期的工具类，在日常开发中经常会用到，但是由于它是线程不安全的，所以多线程共用...
概述
SimpleDateFormat是Java提供的一个格式化和解析日期的工具类，在日常开发中经常会用到，但是由于它是线程不安全的，所以多线程共用一个SimpleDateFormat实例对日期进行解析或者格式化会导致程序出错。
这里来揭示它为何是线程不安全的，以及如何避免该问题。
复现问题
import java.text.ParseException;
import java.text.SimpleDateFormat;
/**
* @author 小工匠
* @version 1.0
* @description: TODO
* @date 2021/11/21 14:56
* @mark: show me the code , change the world
*/
public class SimpleDateFormatTest {
// 1 创建单例实例
private static SimpleDateFormat sdf = new SimpleDateFormat("YYYY-MM-dd HH:mm:ss");
public static void main(String[] args) {
// 2 开启多个线程，并且欧东
for (int i = 0; i < 10; i++) {
Thread thread = new Thread(() -> {
try {
// 3 使用单例日期解析文本
System.out.println(sdf.parse("2021-11-19 15:15:00"));
} catch (ParseException e) {
e.printStackTrace();
}
});
thread.start();
}
}
}
代码（1）创建了SimpleDateFormat的一个实例
代码（2）创建10个线程，每个线程都共用同一个sdf对象对文本日期进行解析。
多运行几次代码就会抛出java.lang.NumberFormatException异常，增加线程的个数有利于复现该问题
Exception in thread "Thread-0" Exception in thread "Thread-2" Exception in thread "Thread-1" Exception in thread "Thread-6" Exception in thread "Thread-4" Exception in thread "Thread-8" Exception in thread "Thread-9" Exception in thread "Thread-5" Exception in thread "Thread-7" java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Long.parseLong(Long.java:601)
at java.lang.Long.parseLong(Long.java:631)
at java.text.DigitList.getLong(DigitList.java:195)
at java.text.DecimalFormat.parse(DecimalFormat.java:2084)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.ArrayIndexOutOfBoundsException: 20
at java.text.DigitList.append(DigitList.java:151)
at java.text.DecimalFormat.subparse(DecimalFormat.java:2278)
at java.text.DecimalFormat.parse(DecimalFormat.java:2036)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: multiple points
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at java.text.DigitList.getDouble(DigitList.java:169)
at java.text.DecimalFormat.parse(DecimalFormat.java:2089)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Long.parseLong(Long.java:601)
at java.lang.Long.parseLong(Long.java:631)
at java.text.DigitList.getLong(DigitList.java:195)
at java.text.DecimalFormat.parse(DecimalFormat.java:2084)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at java.text.DigitList.getDouble(DigitList.java:169)
at java.text.DecimalFormat.parse(DecimalFormat.java:2089)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at java.text.DigitList.getDouble(DigitList.java:169)
at java.text.DecimalFormat.parse(DecimalFormat.java:2089)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.ArrayIndexOutOfBoundsException: 19
at java.text.DigitList.append(DigitList.java:151)
at java.text.DecimalFormat.subparse(DecimalFormat.java:2278)
at java.text.DecimalFormat.parse(DecimalFormat.java:2036)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: multiple points
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at java.text.DigitList.getDouble(DigitList.java:169)
at java.text.DecimalFormat.parse(DecimalFormat.java:2089)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
at java.lang.Double.parseDouble(Double.java:538)
at java.text.DigitList.getDouble(DigitList.java:169)
at java.text.DecimalFormat.parse(DecimalFormat.java:2089)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.artisan.bfzm.chapter11.SimpleDateFormatTest.lambda$main$0(SimpleDateFormatTest.java:26)
at java.lang.Thread.run(Thread.java:748)
Sun Dec 27 15:15:00 CST 2020
源码分析
文章来源: artisan.blog.csdn.net，作者：小小工匠，版权归原作者所有，如需转载，请联系作者。
原文链接：artisan.blog.csdn.net/article/details/121453847
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