SimpleDateFormat非线程安全

「爱情、让人受尽委屈。」 2022-05-22 10:18 255阅读 0赞

**枝上柳绵吹又少,天涯何处无芳草**  
类SimpleDateFormat主要负责日期的转换与格式化，但是在多线程的环境下，使用此类容易造成数据转换及处理的不正确，因为SimpleDateFormat类并不是线程安全的。  
测试代码：

import java.text.SimpleDateFormat; import java.util.Date; public class SimpleDateTest { public static void main(String[] args) { SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); String[] dateStringArray = new String[]{ "2000-01-01","2000-06-01","2000-06-01","2000-11-05","2000-08-01","2014-06-01","2018-10-01","2001-11-05","2013-08-01","2013-08-21"}; MyThread[] myThreads = new MyThread[10]; for (int i = 0 ;i < myThreads.length; i++) { myThreads[i] = new MyThread(sdf,dateStringArray[i]); } for (int i = 0 ;i < 10; i++) { myThreads[i].start(); } } } class MyThread extends Thread { private SimpleDateFormat sdf; private String dateString; public MyThread(SimpleDateFormat sdf,String dateString) { super(); this.sdf = sdf; this.dateString = dateString; } @Override public void run() { try { Date dateRef = sdf.parse(dateString); String newDateString = sdf.format(dateRef).toString(); if (!newDateString.equals(dateString)) { System.out.println("ThreadName=" + this.getName() + "报错了，日期字符串：" + dateString + "转成的日期为：" + newDateString); } }catch (Exception e) { e.printStackTrace(); } } }

运行结果：  
![这里写图片描述][70]  
这样就有很大概率出现转换异常的问题。那么，这个问题如何解决呢？  
解决异常方法一：创建多个SimpleDateFormat对象  
代码：

import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.util.Date;
    
    
    public class SimpleDateTest { 
        public static void main(String[] args) {
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            String[] dateStringArray = new String[]{
       "2000-01-01","2000-06-01","2000-06-01","2000-11-05","2000-08-01","2014-06-01","2018-10-01","2001-11-05","2013-08-01","2013-08-21"};
            MyThread[] myThreads = new MyThread[10];
            for (int i  = 0 ;i < myThreads.length; i++) {
                myThreads[i] = new MyThread(sdf,dateStringArray[i]);
            }
            for (int i  = 0 ;i < 10; i++) {
                myThreads[i].start();
            }
        }
    }
    
    class MyThread extends Thread {
        private SimpleDateFormat sdf;
        private String dateString;
        public MyThread(SimpleDateFormat sdf,String dateString) {
            super();
            this.sdf = sdf;
            this.dateString = dateString;
        }
        @Override
        public void run() {
            try {
                Date dateRef = dateTools.parse("yyyy-MM-dd",dateString);
                String newDateString = dateTools.format("yyyy-MM-dd",dateRef).toString();
                if (!newDateString.equals(dateString)) {
                    System.out.println("ThreadName=" + this.getName() + "报错了，日期字符串：" + dateString + "转成的日期为：" + newDateString);
                }
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    
    class dateTools {
        public static Date parse(String formatPattern,String dateSring) throws ParseException {
            return new SimpleDateFormat(formatPattern).parse(dateSring);
        }
        public static String format(String formatPattern,Date date) throws ParseException {
            return new SimpleDateFormat(formatPattern).format(date);
        }
    }

运行结果：  
![这里写图片描述][70 1]  
解决异常方法二：使用ThreadLocal类绑定到指定对象，也可以解决该问题。  
测试代码：

import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.util.Date;
    
    
    public class SimpleDateTest { 
        public static void main(String[] args) {
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            String[] dateStringArray = new String[]{
       "2000-01-01","2000-06-01","2000-06-01","2000-11-05","2000-08-01","2014-06-01","2018-10-01","2001-11-05","2013-08-01","2013-08-21"};
            MyThread[] myThreads = new MyThread[10];
            for (int i  = 0 ;i < myThreads.length; i++) {
                myThreads[i] = new MyThread(sdf,dateStringArray[i]);
            }
            for (int i  = 0 ;i < 10; i++) {
                myThreads[i].start();
            }
        }
    }
    
    class MyThread extends Thread {
        private SimpleDateFormat sdf;
        private String dateString;
        public MyThread(SimpleDateFormat sdf,String dateString) {
            super();
            this.sdf = sdf;
            this.dateString = dateString;
        }
        @Override
        public void run() {
            try {
                Date dateRef = dateTools.getSimpleDateFormat("yyyy-MM-dd").parse(dateString);
                String newDateString = dateTools.getSimpleDateFormat("yyyy-MM-dd").format(dateRef).toString();
                if (!newDateString.equals(dateString)) {
                    System.out.println("ThreadName=" + this.getName() + "报错了，日期字符串：" + dateString + "转成的日期为：" + newDateString);
                }
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    
    class dateTools {
        public static ThreadLocal<SimpleDateFormat> tl = new ThreadLocal<>();
        public static SimpleDateFormat getSimpleDateFormat(String formatPattern) {
            SimpleDateFormat sdf = null;
            if (sdf == null) {
                sdf = new SimpleDateFormat(formatPattern);
                tl.set(sdf);
            }
            return sdf;
        }
    }

![这里写图片描述][70 2]  
使用这两种方法，都没有出现异常，说明异常已经被我们解决了。

[70]: /images/20220522/e0759cd390e54398a23464b6a5dc0af2.png
[70 1]: /images/20220522/d5d2ee9dd5784296b369d32c89707b16.png
[70 2]: /images/20220522/64bdd094c3d6439a8fff5e9b361dc34a.png