SimpleDateFormatNumber FormatException 格式化错误

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SimpleDateFormatNumber FormatException 格式化错误

看源码，发现 SimpleDateFormatNumber 不是线程安全的类。

 * Date formats are not synchronized.* It is recommended to create separate format instances for each thread.* If multiple threads access a format concurrently, it must be synchronized* externally.

因为，SimpleDateFormat继承了DateFormat,在DateFormat中定义了一个protected属性的 Calendar类的对象：calendar。只是因为Calendar累的概念复杂，牵扯到时区与本地化等等，Jdk的实现中使用了成员变量来传递参数，这就造成在多线程的时候会出现错误。

这样写，在高并发的情况下会出现  java.lang.NumberFormatException: For input string: ""

public class DateUtil {private DateUtil(){}private static final DateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");public static Date parse(String date)  throws ParseException {return DATE_FORMAT.parse(date);}    }

改成：

public class DateUtil {private DateUtil(){}public static Date parse(String date)  throws ParseException {return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(date);}    }

或者： 

public class DateUtil {private DateUtil(){}private static final DateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");public static Date parse(String date)  throws ParseException {synchronized(DATE_FORMAT){return DATE_FORMAT.parse(date);}}    }

附JDK1.8时间获取

        //JDK1.8时间获取当前时间String now = LocalDateTime.now().withNano(0).toString().replace("T", " ");String now = LocalDate.now()+" "+LocalTime.now().withNano(0).toString();