SimpleDateFormat-多线程问题

SimpleDateFormat-多线程问题：

　　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

 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;

 /**
  *    线程类
  */
 public class MyThread extends Thread {

     private SimpleDateFormat sdf;
     private String dateString;

     public MyThread(SimpleDateFormat sdf,String dateString) {
         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 = " + Thread.currentThread().getName()
                         + "报错了  日期字符串：" + dateString + "转换成日期为：" + newDateString);
             }
         } catch (ParseException e) {
             e.printStackTrace();
         }
     }
 }

 import java.text.SimpleDateFormat;

 public class Test {

     /**
      *    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
      */
     public static void main(String[] args) {
         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
         String[] dateStringArray = new String[] {
                 "2000-01-01","2000-01-02","2000-01-03",
                 "2000-01-04","2000-01-05","2000-01-06",
                 "2000-01-07","2000-01-08","2000-01-09",
                 "2000-01-10"
         };

         MyThread[] threadArray = new MyThread[10];
         for (int i = 0; i < 10; i++) {
             threadArray[i] = new MyThread(sdf, dateStringArray[i]);
         }
         for (int i = 0; i < 10; i++) {
             threadArray[i].start();
         }
     }
 }

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：

 import java.text.ParseException;
 import java.util.Date;

 /**
  *    线程类
  */
 public class MyThread extends Thread {

     private String dateString;
     public MyThread(String dateString) {
         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 = " + Thread.currentThread().getName()
                         + "报错了  日期字符串：" + dateString + "转换成日期为：" + newDateString);
             }
         } catch (ParseException e) {
             e.printStackTrace();
         }
     }
 }

 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;

 /**
  *    日期格式化工具类
  */
 public class DateTools {

     public static Date parse(String formatPattern,String dateString) throws ParseException {
         return new SimpleDateFormat(formatPattern).parse(dateString);
     }

     public static String format(String formatPattern,Date date) throws ParseException {
         return new SimpleDateFormat(formatPattern).format(date).toString();
     }
 }

 public class Test {

     /**
      *    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，
      *    原理：创建了多个SimpleDateFormat实例
      */
     public static void main(String[] args) {
         String[] dateStringArray = new String[] {
                 "2000-01-01","2000-01-02","2000-01-03",
                 "2000-01-04","2000-01-05","2000-01-06",
                 "2000-01-07","2000-01-08","2000-01-09",
                 "2000-01-10"
         };

         MyThread[] threadArray = new MyThread[10];
         for (int i = 0; i < 10; i++) {
             threadArray[i] = new MyThread(dateStringArray[i]);
         }
         for (int i = 0; i < 10; i++) {
             threadArray[i].start();
         }
     }
 }

　　解决多线程出现的问题-使用ThreadLocal：

 import java.text.ParseException;
 import java.util.Date;

 /**
  *    线程类
  */
 public class MyThread extends Thread {

     private String dateString;
     public MyThread(String dateString) {
         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 = " + Thread.currentThread().getName()
                         + "报错了  日期字符串：" + dateString + "转换成日期为：" + newDateString);
             }
         } catch (ParseException e) {
             e.printStackTrace();
         }
     }
 }

 import java.text.SimpleDateFormat;

 /**
  *    日期格式化工具类,使用ThreadLocal解决SimpleDateFormat非线程安全问题
  */
 public class DateTools {

     private static ThreadLocal<SimpleDateFormat> t1 = new ThreadLocal<>();

     public static SimpleDateFormat getSimpleDateFormat(String datePattern) {
         SimpleDateFormat sdf = null;
         sdf = t1.get();
         if(sdf == null) {
             sdf = new SimpleDateFormat(datePattern);
             t1.set(sdf);
         }
         return sdf;
     }
 }

 public class Test {

     /**
      *    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
      *    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
      */
     public static void main(String[] args) {
         String[] dateStringArray = new String[] {
                 "2000-01-01","2000-01-02","2000-01-03",
                 "2000-01-04","2000-01-05","2000-01-06",
                 "2000-01-07","2000-01-08","2000-01-09",
                 "2000-01-10"
         };

         MyThread[] threadArray = new MyThread[10];
         for (int i = 0; i < 10; i++) {
             threadArray[i] = new MyThread(dateStringArray[i]);
         }
         for (int i = 0; i < 10; i++) {
             threadArray[i].start();
         }
     }
 }