在需要的時(shí)候創(chuàng)建實(shí)例

public static String format(Date date) throws Exception {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    return sdf.format(date);
}

public static Date parse(String strDate) throws Exception {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    return sdf.parse(strDate);
}

缺點(diǎn)：每次調(diào)用方法都要?jiǎng)?chuàng)建和銷(xiāo)毀sdf對(duì)象，效率較低。

synchronized

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

public static String format(Date date) throws Exception {
    synchronized(sdf){
        return sdf.format(date);
    }
}

public static Date parse(String strDate) throws Exception {
    synchronized(sdf){
        return sdf.parse(strDate);    
    }
}

缺點(diǎn)：并發(fā)量大時(shí)線程阻塞，對(duì)性能有影響。

ThreadLocal

ThreadLocal可以讓每個(gè)線程都得到一個(gè)sdf對(duì)象

private static ThreadLocal<DateFormat> threadLocal = new ThreadLocal<DateFormat>() {
    @Override
    protected DateFormat initialValue() {
        return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    }
};

public static Date parse(String strDate) throws Exception {
    return threadLocal.get().parse(strDate);
}

public static String format(Date date) throws Exception {
    return threadLocal.get().format(date);
}

基于JDK1.8的DateTimeFormatter(線程安全的類(lèi))

private static final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

public static String format(LocalDateTime date) throws Exception {
    return dtf.format(date);
}

public static LocalDateTime parse(String strDate) {
    return LocalDateTime.parse(strDate, dtf);
}