Java获取当前时间：多种方法详解与性能对比，轻松解决时间处理难题

long currentTime = System.currentTimeMillis(); System.out.println("当前时间戳：" + currentTime);

LocalDateTime now = LocalDateTime.now(); System.out.println("当前本地时间：" + now);

// 获取时间的各个部分 int year = now.getYear(); Month month = now.getMonth(); int day = month.getValue(); int hour = now.getHour(); int minute = now.getMinute();

System.out.println(year + "年" + day + "月" + now.getDayOfMonth() + "日 " +

               hour + "时" + minute + "分");

Date now = new Date(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); String formatted = sdf.format(now); System.out.println("格式化时间：" + formatted);

// 更多格式示例 SimpleDateFormat dateOnly = new SimpleDateFormat("yyyy年MM月dd日"); SimpleDateFormat timeOnly = new SimpleDateFormat("HH时mm分ss秒");

System.out.println("仅日期：" + dateOnly.format(now)); System.out.println("仅时间：" + timeOnly.format(now));

// 获取时间戳的多种方式 long timestamp1 = System.currentTimeMillis(); long timestamp2 = Instant.now().toEpochMilli(); long timestamp3 = new Date().getTime();

System.out.println("当前时间戳：" + timestamp1); System.out.println("Instant时间戳：" + timestamp2); System.out.println("Date时间戳：" + timestamp3);

// 时间戳转换为可读时间 Instant instant = Instant.ofEpochMilli(timestamp1); LocalDateTime dateTime = LocalDateTime.ofInstant(instant, ZoneId.systemDefault()); System.out.println("时间戳对应时间：" + dateTime);

// 性能测试示例 public class TimePerformanceTest {

public static void main(String[] args) {
    int iterations = 1_000_000;
    
    // System.currentTimeMillis()
    long start1 = System.nanoTime();
    for (int i = 0; i < iterations; i++) {
        long time = System.currentTimeMillis();
    }
    long duration1 = System.nanoTime() - start1;
    
    // Instant.now()
    long start2 = System.nanoTime();
    for (int i = 0; i < iterations; i++) {
        Instant instant = Instant.now();
    }
    long duration2 = System.nanoTime() - start2;
    
    // new Date()
    long start3 = System.nanoTime();
    for (int i = 0; i < iterations; i++) {
        Date date = new Date();
    }
    long duration3 = System.nanoTime() - start3;
    
    System.out.println("System.currentTimeMillis(): " + duration1 / 1_000_000 + " ms");
    System.out.println("Instant.now(): " + duration2 / 1_000_000 + " ms");
    System.out.println("new Date(): " + duration3 / 1_000_000 + " ms");
}

}

// 错误示例 - 非线程安全 public class UnsafeTimeFormatter {

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

public String formatDate(Date date) {
    return formatter.format(date);  // 多线程下可能出错
}

}

// 正确做法 - 使用ThreadLocal public class SafeTimeFormatter {

private static final ThreadLocal<SimpleDateFormat> formatter =
    ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));

public String formatDate(Date date) {
    return formatter.get().format(date);
}

}

// 更好的选择 - 使用DateTimeFormatter public class ModernTimeFormatter {

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

public String formatDate(LocalDateTime dateTime) {
    return dateTime.format(formatter);  // 线程安全
}

}