SimpleDateFormat的线程安全问题

我就是我 2023-06-06 13:27 22阅读 0赞

SimpleDateFormat类在多线程环境下中处理日期，极易出现日期转换错误的情况  
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1 import java.text.ParseException;  
2 import java.text.SimpleDateFormat;  
3 import java.util.Date;  
4  
5 /\*\*  
6 \* 线程类  
7 */  
8 public class MyThread extends Thread \{  
9  
10 private SimpleDateFormat sdf;  
11 private String dateString;  
12  
13 public MyThread(SimpleDateFormat sdf,String dateString) \{  
14 this.sdf = sdf;  
15 this.dateString = dateString;  
16 \}  
17  
18 @Override  
19 public void run() \{  
20 try \{  
21 Date dateRef = sdf.parse(dateString);  
22 String newDateString = sdf.format(dateRef).toString();  
23 if(!newDateString.equals(dateString)) \{  
24 System.out.println("ThreadName = " + Thread.currentThread().getName()  
25 + “报错了 日期字符串：” + dateString + “转换成日期为：” + newDateString);  
26 \}  
27 \} catch (ParseException e) \{  
28 e.printStackTrace();  
29 \}  
30 \}  
31 \}  
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1 import java.text.SimpleDateFormat;  
2  
3 public class Test \{  
4  
5 /*\*  
6 \* 测试单例的SimpleDateFormat类在多线程环境下中处理日期，极易出现日期转换错误的情况  
7 \*/  
8 public static void main(String\[\] args) \{  
9 SimpleDateFormat sdf = new SimpleDateFormat(“yyyy-MM-dd”);  
10 String\[\] dateStringArray = new String\[\] \{  
11 “2000-01-01”,“2000-01-02”,“2000-01-03”,  
12 “2000-01-04”,“2000-01-05”,“2000-01-06”,  
13 “2000-01-07”,“2000-01-08”,“2000-01-09”,  
14 “2000-01-10”  
15 \};  
16  
17 MyThread\[\] threadArray = new MyThread\[10\];  
18 for (int i = 0; i < 10; i++) \{  
19 threadArray\[i\] = new MyThread(sdf, dateStringArray\[i\]);  
20 \}  
21 for (int i = 0; i < 10; i++) \{  
22 threadArray\[i\].start();  
23 \}  
24 \}  
25 \}  
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运行之后会输出很多的错误信息！

解决多线程出现的问题-为每个线程实例一个SimpleDateFormat：  
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1 import java.text.ParseException;  
2 import java.util.Date;  
3  
4 /\*\*  
5 \* 线程类  
6 */  
7 public class MyThread extends Thread \{  
8  
9 private String dateString;  
10 public MyThread(String dateString) \{  
11 this.dateString = dateString;  
12 \}  
13  
14 @Override  
15 public void run() \{  
16 try \{  
17 Date dateRef = DateTools.parse(“yyyy-MM-dd”, dateString);  
18 String newDateString = DateTools.format(“yyyy-MM-dd”,dateRef).toString();  
19 if(!newDateString.equals(dateString)) \{  
20 System.out.println("ThreadName = " + Thread.currentThread().getName()  
21 + “报错了 日期字符串：” + dateString + “转换成日期为：” + newDateString);  
22 \}  
23 \} catch (ParseException e) \{  
24 e.printStackTrace();  
25 \}  
26 \}  
27 \}  
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1 import java.text.ParseException;  
2 import java.text.SimpleDateFormat;  
3 import java.util.Date;  
4  
5 /*\*  
6 \* 日期格式化工具类  
7 */  
8 public class DateTools \{  
9  
10 public static Date parse(String formatPattern,String dateString) throws ParseException \{  
11 return new SimpleDateFormat(formatPattern).parse(dateString);  
12 \}  
13  
14 public static String format(String formatPattern,Date date) throws ParseException \{  
15 return new SimpleDateFormat(formatPattern).format(date).toString();  
16 \}  
17 \}  
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1 public class Test \{  
2  
3 /*\*  
4 \* 测试,运行程序后，控制台没有任何输出，也就是转换没有任何异常，  
5 \* 原理：创建了多个SimpleDateFormat实例  
6 */  
7 public static void main(String\[\] args) \{  
8 String\[\] dateStringArray = new String\[\] \{  
9 “2000-01-01”,“2000-01-02”,“2000-01-03”,  
10 “2000-01-04”,“2000-01-05”,“2000-01-06”,  
11 “2000-01-07”,“2000-01-08”,“2000-01-09”,  
12 “2000-01-10”  
13 \};  
14  
15 MyThread\[\] threadArray = new MyThread\[10\];  
16 for (int i = 0; i < 10; i++) \{  
17 threadArray\[i\] = new MyThread(dateStringArray\[i\]);  
18 \}  
19 for (int i = 0; i < 10; i++) \{  
20 threadArray\[i\].start();  
21 \}  
22 \}  
23 \}  
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　　解决多线程出现的问题-使用ThreadLocal：  
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1 import java.text.ParseException;  
2 import java.util.Date;  
3  
4 /*\*  
5 \* 线程类  
6 */  
7 public class MyThread extends Thread \{  
8  
9 private String dateString;  
10 public MyThread(String dateString) \{  
11 this.dateString = dateString;  
12 \}  
13  
14 @Override  
15 public void run() \{  
16 try \{  
17 Date dateRef = DateTools.getSimpleDateFormat(“yyyy-MM-dd”).parse(dateString);  
18 String newDateString = DateTools.getSimpleDateFormat(“yyyy-MM-dd”).format(dateRef).toString();  
19 if(!newDateString.equals(dateString)) \{  
20 System.out.println("ThreadName = " + Thread.currentThread().getName()  
21 + “报错了 日期字符串：” + dateString + “转换成日期为：” + newDateString);  
22 \}  
23 \} catch (ParseException e) \{  
24 e.printStackTrace();  
25 \}  
26 \}  
27 \}  
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1 import java.text.SimpleDateFormat;  
2  
3 /*\*  
4 \* 日期格式化工具类,使用ThreadLocal解决SimpleDateFormat非线程安全问题  
5 */  
6 public class DateTools \{  
7  
8 private static ThreadLocal t1 = new ThreadLocal<>();  
9  
10 public static SimpleDateFormat getSimpleDateFormat(String datePattern) \{  
11 SimpleDateFormat sdf = null;  
12 sdf = t1.get();  
13 if(sdf == null) \{  
14 sdf = new SimpleDateFormat(datePattern);  
15 t1.set(sdf);  
16 \}  
17 return sdf;  
18 \}  
19 \}  
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1 public class Test \{  
2  
3 /*\*  
4 \* 测试,运行程序后，控制台没有任何输出，也就是转换没有任何异常  
5 \* 原理：每个线程都会有自己的ThreadLocal存储全局变量，也就是每个线程都有自己的SimpleDateFormat实例  
6 \*/  
7 public static void main(String\[\] args) \{  
8 String\[\] dateStringArray = new String\[\] \{  
9 “2000-01-01”,“2000-01-02”,“2000-01-03”,  
10 “2000-01-04”,“2000-01-05”,“2000-01-06”,  
11 “2000-01-07”,“2000-01-08”,“2000-01-09”,  
12 “2000-01-10”  
13 \};  
14  
15 MyThread\[\] threadArray = new MyThread\[10\];  
16 for (int i = 0; i < 10; i++) \{  
17 threadArray\[i\] = new MyThread(dateStringArray\[i\]);  
18 \}  
19 for (int i = 0; i < 10; i++) \{  
20 threadArray\[i\].start();  
21 \}  
22 \}  
23 \}