SimpleDateFormat简介及替代方案

SimpleDateFormat简介及替代方案 简介

SimpleDateFormat是一个时间格式化工具，可以将字符串格式化时间Date类型，也可以将Date类型格式化为字符串String类型，但其线程不安全。

常用方法

public final String format(Date date):将时间格式化为我们想要的字符串。

public Date parse(String source):将字符串格式化为Date类型。

代码

• format方法

static SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    static ArrayList<Date>  list=new ArrayList<>();

    static {

        // 每个线程对应处理的Date对象

        // 我将会开启10个线程

        Date date1 = new Date(2011-1900, Calendar.JANUARY,1);

        Date date2 = new Date(2012-1900, Calendar.JANUARY,1);

        Date date3 = new Date(2013-1900, Calendar.JANUARY,1);

        Date date4 = new Date(2014-1900, Calendar.JANUARY,1);

        Date date5 = new Date(2015-1900, Calendar.JANUARY,1);

        Date date6 = new Date(2016-1900, Calendar.JANUARY,1);

        Date date7 = new Date(2017-1900, Calendar.JANUARY,1);

        Date date8 = new Date(2018-1900, Calendar.JANUARY,1);

        Date date9 = new Date(2019-1900, Calendar.JANUARY,1);

        Date date10 = new Date(2020-1900, Calendar.JANUARY,1);

        list.add(date1);

        list.add(date2);

        list.add(date3);

        list.add(date4);

        list.add(date5);

        list.add(date6);

        list.add(date7);

        list.add(date8);

        list.add(date9);

        list.add(date10);

    }

    /**

     *  线程不安全

     *  线程执行前和执行后，数据不一致

     *

     *

     **/

    public void formatdemo(){

        ExecutorService service= Executors.newCachedThreadPool();

        for (int i = 0; i < 10; i++) {

            final int t = i;

            service.execute(()->{

                try {

                    TimeUnit.MILLISECONDS.sleep(500);

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

                Date date = list.get(t);

                String format = SimpleDateFormatDemo.format.format(date);

                System.out.println("线程"+Thread.currentThread().getName()+" 执行前: "+date);

                System.out.println("线程"+Thread.currentThread().getName()+" 执行结果后:"+format);

            });

        }

    }

• 执行结果
  
  

线程3执行前 和 执行后结果不一致，说明线程不安全

• parse方法

public void parsedemo(){

        ExecutorService service= Executors.newCachedThreadPool();

        for (int i = 0; i < 10; i++) {

            final int t = i;

            service.execute(()->{

                try {

                    TimeUnit.MILLISECONDS.sleep(500);

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

                try {

                    System.out.println("线程"+Thread.currentThread().getName()+" 执行结果后:"+format.parse("2021-12-12 12:23:23"));

                } catch (ParseException e) {

                    e.printStackTrace();

                }

            });

        }

    }

• 执行结果
  
  出现异常: Exception in thread "pool-1-thread-1" java.lang.NumberFormatException: multiple points

线程不安全

解决办法

使用ThreadLocal进行替代

代码

public static  final ThreadLocal<DateFormat> df=new ThreadLocal<DateFormat>(){

        @Override

        protected DateFormat initialValue() {

            return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        }

    };

    static ArrayList<Date> list=new ArrayList<>();

    static {

        // 每个线程对应处理的Date对象

        // 我将会开启10个线程

        Date date1 = new Date(2011-1900, Calendar.JANUARY,1);

        Date date2 = new Date(2012-1900, Calendar.JANUARY,1);

        Date date3 = new Date(2013-1900, Calendar.JANUARY,1);

        Date date4 = new Date(2014-1900, Calendar.JANUARY,1);

        Date date5 = new Date(2015-1900, Calendar.JANUARY,1);

        Date date6 = new Date(2016-1900, Calendar.JANUARY,1);

        Date date7 = new Date(2017-1900, Calendar.JANUARY,1);

        Date date8 = new Date(2018-1900, Calendar.JANUARY,1);

        Date date9 = new Date(2019-1900, Calendar.JANUARY,1);

        Date date10 = new Date(2020-1900, Calendar.JANUARY,1);

        list.add(date1);

        list.add(date2);

        list.add(date3);

        list.add(date4);

        list.add(date5);

        list.add(date6);

        list.add(date7);

        list.add(date8);

        list.add(date9);

        list.add(date10);

    }

    /**

     *  线程不安全

     *  线程执行前和执行后，数据不一致

     *

     *

     **/

    public void formatdemo(){

        ExecutorService service= Executors.newCachedThreadPool();

        for (int i = 0; i < 10; i++) {

            final int t = i;

            service.execute(()->{

                try {

                    TimeUnit.MILLISECONDS.sleep(500);

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

                Date date = list.get(t);

                System.out.println("线程"+Thread.currentThread().getName()+" 执行前: "+date);

                System.out.println("线程"+Thread.currentThread().getName()+" 执行结果后:"+ df.get().format(date));

            });

        }

    }

    /**

     *  Exception in thread "pool-1-thread-1" java.lang.NumberFormatException: multiple points

     *  线程不安全

     **/

    public void parsedemo(){

        ExecutorService service= Executors.newCachedThreadPool();

        for (int i = 0; i < 10; i++) {

            final int t = i;

            service.execute(()->{

                try {

                    TimeUnit.MILLISECONDS.sleep(500);

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

                try {

                    System.out.println("线程"+Thread.currentThread().getName()+" 执行结果后:"+df.get().parse("2021-12-12 12:23:23"));

                } catch (ParseException e) {

                    e.printStackTrace();

                }

            });

        }

    }

Gitee地址

https://gitee.com/zhuayng/foundation-study/tree/develop/JavaBasis/Tools/src/main/java/com/yxkj/javabasistools/tools/date