blocks|key|1670202|text|尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1670203|Calendar+calendar+=+Calendar.getInstance();
calendar.setTimeInMillis(timeStamp);|code-block|syntax|javascript|1670204|或者：|1670205|Date+date+=+new+Date(milliseconds);|1670206|但不确定哪个更快。|1670207|要将日期格式化为字符串，可以使用SimpleDateFormat：|1670208|SimpleDateFormat+sdf+=+new+SimpleDateFormat("yyyyMMdd+HHmmss.SSS");+//+should+output+something+like+you+desired:+20141220+174522.23
String+formattedDate+=+sdf.format(date);+|1670209|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Try:

<pre><code>Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(timeStamp);
</code></pre>

Or:

<pre><code>Date date = new Date(milliseconds);
</code></pre>

Not sure which one is faster though.

To format the Date into a string, you can use SimpleDateFormat:

<pre><code>SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HHmmss.SSS"); // should output something like you desired: 20141220 174522.23
String formattedDate = sdf.format(date); 
</code></pre>

blocks|key|1670261|text|Apache的FastDateFormat类绝对是SimpleDateFormat的一个很好的替代方案。它是快速的，也是线程安全的(特别是在多线程服务器环境中有用)。所有模式都与SimpleDateFormat兼容(时区和某些年份模式除外)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1670262|构造函数的摘要如下：|1670263|FastDateFormat(String+pattern,+TimeZone+timeZone,+Locale+locale)|1670264|您可以在FastDateFormat上找到更多信息。|1670265|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/time/FastDateFormat.html^0|7|E|P|G|2H|G|0|0|0|1S|0|4|E|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|14|8|@]|D|@$9|15|A|16|1|17]]|E|$]]|$1|L|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

Apache Commons Lang's <code>FastDateFormat</code> class is absolutely a good alternative to <code>SimpleDateFormat</code>. It's fast and also Thread-Safe ( especially usefull in multi-threaded server environments). All patterns are compatible with <code>SimpleDateFormat</code> (except time zones and some year patterns).

The summary of the constructor is :

<code>FastDateFormat(String pattern, TimeZone timeZone, Locale locale)</code>

You could find more info at <a href="http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/time/FastDateFormat.html" rel="nofollow"> FastDateFormat</a>

blocks|key|1294191|text|最快的实现很可能是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1294192|Long.toString(millis);|code-block|syntax|javascript|1294193|如果性能是最重要的，那么您应该使用它。|1294194|实际上，我不想使用SimpleDateFormat，因为我认为它的灵活性带来了太多的开销。|blockquote|1294195|根据一个快速的jmh基准，在我的笔记本电脑上，Long.toString每秒得到1200万次运算，SimpleDateFormat是200万次。|offset|length|style|CODE|1294196|你的预算是多少？一旦你知道了，你就能决定哪一个是最合适的。|1294197|entityMap|0|LINK|mutability|MUTABLE|url|http://openjdk.java.net/projects/code-tools/jmh/^0|0|0|0|0|N|D|1D|G|7|3|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|13|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|14|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|15|8|@$N|16|O|17|P|Q]|$N|18|O|19|P|Q]]|9|@$N|1A|O|1B|1|1C]]|A|$]]|$1|R|3|S|5|6|7|1D|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|U|$V|$5|W|X|Y|A|$Z|10]]]]

The fastest implementation is very likely to be:

<pre><code>Long.toString(millis);
</code></pre>

If performance is the most important thing, you should use that.

<blockquote>
 Actually I don't want to use SimpleDateFormat, since I believe its flexibility comes with too much overhead.
</blockquote>

According to a quick <a href="http://openjdk.java.net/projects/code-tools/jmh/" rel="nofollow">jmh</a> benchmark, on my laptop, <code>Long.toString</code> gets twelve million ops/second and <code>SimpleDateFormat</code> is two million.

What's your budget? Once you know that you'll be able to decide which of those is most appropriate.

blocks|key|2909108|text|易于使用，合理快速：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2909109|//+All+Java+versions:
new+java.sql.Timestamp(millis).toString();+//+2016-10-29+12:28:41.979

//+Recommended+when+using+Java+8%2B+(about+%2B50%25+faster+than+Timestamp),+standards+compliant+format
//+checked+with+jmh+1.15
java.time.Instant.ofEpochMilli(millis).toString();+//+2016-10-29T10:28:41.979Z|code-block|syntax|javascript|2909110|entityMap^0|0|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Easy to use and reasonable fast:

<pre><code>// All Java versions:
new java.sql.Timestamp(millis).toString(); // 2016-10-29 12:28:41.979

// Recommended when using Java 8+ (about +50% faster than Timestamp), standards compliant format
// checked with jmh 1.15
java.time.Instant.ofEpochMilli(millis).toString(); // 2016-10-29T10:28:41.979Z
</code></pre>

We have some timestamps represented as long in millis since epoch. Within strings for logging, exceptions, or <code>toString()</code> methods, these timestamps need to be formatted. A simple and clean format is enough.

So, what is the simplest and fastest method for formatting a timestamp in Java?

Requirements:

<ul>
<li>input timestamps represented as long in millis since epoch</li>
<li>output should be a string</li>
<li>fast</li>
<li>low CG overhead</li>
<li>a simple and clean output is sufficient, since it is only for internal purposes (debugging and logging), e.g. something minimal: 20141220 174522.23</li>
<li>if possible within JDK</li>
<li>the time zone is the system time zone</li>
</ul>

In particular, did somebody did a benchmark of JDK methods that can be used for this?

Actually I don't want to use SimpleDateFormat, since I believe its flexibility comes with too much overhead.

Easy and fast way to format a timestamp

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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问格式化时间戳的简单快捷的方法
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