SimpleDateFormat类非线程安全

川长思鸟来 2023-10-28 00:47 151阅读 0赞

SimpleDateFormat在多线程中会出现线程安全问题。

class DateThread extends Thread {
        private SimpleDateFormat sdf;
        private String dateString;
    
        public DateThread(SimpleDateFormat sdf, String dateString) {
            this.sdf = sdf;
            this.dateString = dateString;
        }
    
        @Override
        public void run() {
            try {
                Date date = sdf.parse(dateString);
                String newDateString = sdf.format(date).toString();
                if (!newDateString.equals(dateString)) {
                    System.out.println("ThreadName = " + this.getName()
                            + "报错了 日期字符串：" + dateString
                            + " 转换成的日期为" + newDateString);
                }
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
    }
    public class Run3_formatError {
        public static void main(String[] args) {
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            String[] dateStringArray = new String[] {
                    "2018-12-01", "2018-12-02", "2018-12-03", "2018-12-04", "2018-12-05",
                    "2018-12-06", "2018-12-07", "2018-12-08", "2018-12-09", "2018-12-10"
            };
            DateThread[] threads = new DateThread[10];
            for (int i = 0; i < 10; i++) {
                threads[i] = new DateThread(sdf, dateStringArray[i]);
            }
    
            for (int i = 0; i < 10; i++) {
                threads[i].start();
            }
        }
    }

报错：

java.lang.NumberFormatException: For input string: "1212.E12122E2"
    	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    	at java.lang.Long.parseLong(Long.java:589)
    	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:1869)
    	at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
    	at java.text.DateFormat.parse(DateFormat.java:364)
    	at com.brianway.learning.java.multithread.supplement.example3.DateThread.run(Run3_formatError.java:28)
    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.brianway.learning.java.multithread.supplement.example3.DateThread.run(Run3_formatError.java:28)
    ThreadName = Thread-1报错了 日期字符串：2018-12-02 转换成的日期为2222-12-01
    ThreadName = Thread-0报错了 日期字符串：2018-12-01 转换成的日期为2222-12-01

解决：

class DateThread extends Thread {
        private SimpleDateFormat sdf;
        private String dateString;
        //通过本地线程池 解决线程安全问题
        private static ThreadLocal<SimpleDateFormat> tl = new ThreadLocal<SimpleDateFormat>();
        public DateThread(SimpleDateFormat sdf, String dateString) {
            this.sdf = sdf;
            this.dateString = dateString;
        }
        public static SimpleDateFormat getSimpleDateFormat(String datePattern) {
            SimpleDateFormat sdf = null;
            sdf = tl.get();
            if (sdf == null) {
                sdf = new SimpleDateFormat(datePattern);
                tl.set(sdf);
            }
            return sdf;
        }
        @Override
        public void run() {
            try {
    
                Date date = getSimpleDateFormat("yyyy-MM-dd").parse(dateString);
                String newDateString = DateTools2.getSimpleDateFormat("yyyy-MM-dd").format(date).toString();
                System.out.println(newDateString);
                if (!newDateString.equals(dateString)) {
                    System.out.println("ThreadName = " + this.getName()
                            + "报错了 日期字符串：" + dateString
                            + " 转换成的日期为" + newDateString);
                }
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
    }
    public class Run3_formatError {
        public static void main(String[] args) {
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            String[] dateStringArray = new String[] {
                    "2018-12-01", "2018-12-02", "2018-12-03", "2018-12-04", "2018-12-05",
                    "2018-12-06", "2018-12-07", "2018-12-08", "2018-12-09", "2018-12-10"
            };
            DateThread[] threads = new DateThread[10];
            for (int i = 0; i < 10; i++) {
                threads[i] = new DateThread(sdf, dateStringArray[i]);
            }
    
            for (int i = 0; i < 10; i++) {
                threads[i].start();
            }
        }
    }