ThreadLocal 替代synchronized 写法

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public class Test {     public static void main(String[] args) {         ThreadPoolExecutor executor = new ThreadPoolExecutor(20,20,0L, TimeUnit.SECONDS,new LinkedBlockingDeque<>());         for (int i = 0;i<20;i++){             executor.execute(()-> {                 try {                     //System.out.println(DateUtilUnSafe.parse("2020-08-20 20:35:22"));                     System.out.println(DateUtilSafe.parse("2020-08-20 20:35:22"));                 } catch (ParseException e) {                     e.printStackTrace();                 }             });         }           executor.shutdown();       } }

　　

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package ThreadLocal;   import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.logging.SimpleFormatter;   public final class DateUtilUnSafe {       private  static final SimpleDateFormat time = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");   //    /** //     * 加了同步 //     * @param dateStr //     * @return //     * @throws ParseException //     */ //    public static final synchronized Date parse(String dateStr) throws ParseException { //        Date date = null; //        date = time.parse(dateStr); //        return  date; //    }     /**      * 非同步      * @param dateStr      * @return      * @throws ParseException      */     public static  Date parse(String dateStr) throws ParseException {         Date date = null;         date = time.parse(dateStr);         return  date;     } }

　　

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package ThreadLocal;   import java.text.DateFormat; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;   public final class DateUtilSafe {       private  static final ThreadLocal<DateFormat> THREAD_LOCAL = ThreadLocal.withInitial(()->new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));           /**      * 非同步      * @param dateStr      * @return      * @throws ParseException      */     public static final Date parse(String dateStr) throws ParseException {         Date date = null;         date = THREAD_LOCAL.get().parse(dateStr);         THREAD_LOCAL.remove();         return  date;     } }

DateUtilUnSafe如果不加synchronized多线程情况下会出现安全性问题，可以采用synchronized利用锁机制保证安全性，也可以采用

private  static final ThreadLocal<DateFormat> THREAD_LOCAL = ThreadLocal.withInitial(()->new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));  //为每个线程单独提供一份副本，使每个线程互不影响的使用